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Hi-Tech
Royce Creasey
Bike August 1979
AFTER THE FIRST WEEK OR SO, while my mind was still a complete
blank - the result of being asked to write a monthly column for this
august publication - I started to think about just what the hell is
worth writing about every month, concerning motorcycles. Most of the
options are already closed you understand. The obvious solution, to
talk more or less nonstop about sex, drugs and rock 'n' roll,
would result in slight overkill given Mark Williams's expert
dissertations. In addition he's obviously much better connected.
Next bright idea is, of course, the current scene. What's
happening in this great country of ours right now in 1979? Only problem
is, if you cut out the stuff already mentioned and try and limit what's
left to bikes, there's only one answer: nothing. Oh sure, I understand
that yet another one-litre-plus two-wheeled dinosaur will undoubtedly
appear to astonish us any day now. And that all the old ones have yet
again been uselessly tarted-up for another season's selling.
So who gives a shit? I'm a technician by training and simply
looking at things like that offends my sense of engineering rightness,
let alone dignity. I'm a Human Being by birth and having to live on the
same planet as all that chromium-plated multi-cylinder crap makes me
ill. It's not, you understand, that I consider the manufacturers the
culprits for this state of affairs. If people didn't show such
enthusiasm for buying the stuff, presumably because they believe
adverts, no-one would make it.
Fortunately for the monthly cheque that motivates me to
attempt the fearsome task of doing anything regularly, there are a
couple of bikes that hold my interest; both provide an experience I
value. One is so old that Englishmen, now adult, do not recognise the
name and, confronted with it for the first time on a dirty and dented
tank, have difficulty with the pronunciation ('Is it Italian?). This
particular machine does little that cannot be done better and, indeed,
its main virtue is that the experience comes at a price I have been
able to afford for several years now.
The other bike is so new that, apart from a similar difficulty
in pronouncing the name, many people refuse to admit that it's a bike.
As a technician I have to be critical of several features, but at the
same time I must insist that it's the first real step forward in bike
design since the Neracar. Of course, it all comes down to definitions.
I regard a bike as a device to carry one or two people, with two wheels
and an engine.
If you insist the people must sit on it, that the suspension
arrangements must follow the 'safety bicycle' layout finalised by the
Victorians, that's okay with me. I assume you will show a similar
tolerance when I refer to such machines as motorised bicycles. I'm not
putting them down you understand, after all I own a motorised bicycle
myself and regularly get right off on it. It's just that the
possibility of doing it better, getting off even more, not getting cold
and wet, being able to hit cars with some degree of immunity, using
riding techniques that are simply unavailable with a motorised bicycle,
fires my imagination. Furthermore, due to great good luck or something,
I've experienced the reality of riding a modern bike and I know.
Only thing is that the Quasar is a commercial operation, or at
least that's what I'm told, and it's considered bad form to be
exclusively into one manufacturer's bike. In truth I'm not, it's just
that no-one else makes bikes at the moment, but it's still true that
no-one, least of all our good editor, would tolerate an article each
month on the Quasar. This means that The Velocette and The Quasar are
not going to figure prominently.
What is going to figure is the bike I'd like. Although its
creation is still fantasy, it is based on reality and if l had the
time, a fully equipped workshop, and didn't spend nearly all my time
enjoying it, I would certainly build it. In the meantime, I expect to
have a thoroughly good time writing about it. Consider it a design
exercise if you must put names to things. Putting together the various
components used in a bike is a fascinating process of first defining
the best way of doing each job, solving each problem, and then
developing those components to produce a machine in which they will all
work in harmony.
In the real world this process, when it happens at all, takes
years. There is no way of solving the interactive problems caused by
any working collection of components other than by first experiencing
them, later defining them, and eventually eliminating those which prove
unacceptable. Hopefully without causing any new problems. At this
stage an ability to accept what cannot be changed, to change what
cannot be accepted, is as vital as the wisdom to know the difference.
Merely writing about it is much easier and does not tend to demonstrate
one's lack of wisdom or ability quite so clearly.
First stage in getting anything together is to decide what it
has to do and, equally important, what abilities will not be required.
For instance, it will obviously be essential that the plot makes
100mph, at least in theory. On the other hand, it won't have to be good
at climbing rocky stream beds, although it will certainly have to be
drivable off-road. Fuel consumption needs to be in the high 80s, and I
think an all-up weight of around 300 pounds would be nice. It will have
to keep the riders warm, clean and dry, supported in positions of
superb, and probably intimate, comfort. Handling will have to be better
than anything yet seen on two wheels, and all the extras such as
lights, brakes and tape players must be up to good car standards. I'm
looking at a device that will eat miles along country lanes and
European Autostradas with equal grace and dispatch. If it'll do that, I
know towns won't be a problem.
The targets for weight, fuel consumption and speed indicate
that the motor will have to be light in weight and very efficient in
the one area where efficiency matters: thermal efficiency. There's no
need for a particularly high power output from the engine, speed can be
gained in other ways. This cat is going to be skinned like you've never
seen before! Similarly it's clear that the standards set for the
handling require a form of suspension, especially at the front, that
does not suffer the inherent limitations of conventional forks. In
other words, no plunge under braking, well, perhaps just a little for
the sake of feel. No geometry change, unless for the same reason, under
suspension movement.
The ergonomics, that little matter of rider warmth and
comfort, are a straightforward matter of placing the people in a
comfortable position and supporting them adequately, If the suspension
is going to be effective at keeping wheels on the ground, it will
certainly be comfortable to sit on. Naturally, several areas are
related. The 'bodywork', apart from allowing a moderately powerful
engine to run at the ton with minimal drag, will also be used to keep
the crud off the crew. Be nice to have a bit of luggage space as well,
at least enough for a helmet locker.
As Bike is a bit more together than the average comic, and is
hopefully read by people with some idea of what machinery is, I'll
attempt to justify the various design decisions that I make. With any
luck the series will be interesting enough to generate a bit of
feedback from all you other would-be bike engineers, and we can all
have a groovy time discussing the relative merits of taper roller and
ball wheel bearings for months, just like it used to happen in the good
old days before engineering became unfashionable (to coin a phrase).
What will actually happen of course is that various bigots,
dorks and other strange subspecies of Homo Sap will take offence
at suggestions that some feature of a Bike They Own is less than
perfect and send in letters full of hate. No doubt a few stalwart
supporters of the past will object to my style of English too. If you
are one of these people, don't bother to write; pick up on that
excellent group Alberto Y Los Trios Paranoias - they've got a message
for you.
Biggest question for me has little to do with anything
technical. It's just this business of agreeing to write something every
month. I'm sure it's possible. I know lots of people who write
something every day. The question is whether I can keep it together
without running foul of words, ideas or interest. Who knows what we'll
all be doing in six months?
Fortunately there hasn't been any suggestion that I should
sign anything or fill in any forms (both against my religion) so I
guess it's down to going for it and hoping I make it out the other end.
Just like riding a bike. I'm encouraged that so far I've managed to
write enough about writing about the subject to have avoided almost
entirely having anything to do with it. With any luck, by next month
I'll have generated a few more thousand words about what I'm going to
write about later and I'll never have to do anything again. Wonderful:
High-Tech
Royce Creasey
Bike September 1979
Tradition, and a general acceptance of what exists, means that
to obtain the Designer's `clean sheet', the Blue Sky stage, a certain
amount of rubbing out of what is already on that sheet is required. The
Quasar takes a giant step forward in allowing the rider to adopt a
reasonable riding position but it does very little in the clean sheet
field concerning conventional motorcycle design. Let us begin then
with the basic motorcycle design of the very early biking days,
The open-minded approach to design evident in the automobile
field was sadly lacking in the two-wheel world. The pedal cycle was a
child of the 19th century; most of the original designs were inadequate
for the original purpose and the introduction of the 'safety bicycle'
coincided with the appearance of the petrol engine. No sooner had this
innocent device arrived at a practical layout, the one still used
today, than various dangerous lunatics were attempting to cram one of
these new-fangled engines into it.
Just as in the car world, every conceivable way of mounting
the motor and its various ancillaries was tried in those early days.
The crucial point, where we get interested, was that everyone was
working with the basic `safety bicycle' frame. Due to this choice (or
lack thereof) designers were faced with several-major problems, and
like all true enthusiasts they threw themselves into finding solutions
with a fanaticism that has only recently started to waver.
The majority of the safety bicycle will have to be rubbed off
the sheet before we can commence redrawing. The bicycle is the shape it
is because it has to be pedalled. It is an essential feature that the
rider be able to stand on the pedals and, holding onto a conveniently
positioned support, push as hard as possible. I'm not aware of any
necessity to do this if a motor is fitted. Given this requisite, the
bicycle i's a model of elegant simplicity, especially considering the
low weight and moderate power. A simple unsprung front fork is adequate
and has the advantage of placing the handlebars perfectly for support
while pedalling. This pleasant balance of man and machine is abruptly
upset when we fit an engine. The motor and its connected parts will lie
more or less on the plane of the rear spindle, to which it is somehow
connected. This lump of machinery is heavy and a mere glance at the
safety bicycle frame will reveal that any real speed, or an attempt to
reduce said speed by use of a front brake, will result in the frame and
forks bending about the steering head. The loads must follow a path
which resembles the letter V (inverted of course). This tendency to
bend cannot be overcome, only resisted, and that resistance must come
from extra strength in the area where the paths of the forces meet.
Unfortunately, the problem doesn't stop there. Due to the
increased weight and speed of our modified safety bicycle, some form of
front suspension must be fitted, and this is where the problems begin
to multiply. Forks in general have the disadvantage of being heavy and
this weight is part of the steered weight. The success of the
telescopic fork as front suspension is mainly because it's the lightest
available. Motorised bicycles are unique in moving the front suspension
with the steering; everyone else separates the two functions in order
to arrive at a reasonable steering weight.
Naturally, it's worse than that. Telescopic members work well
when they deal with loads in line with their length. Otherwise they
tend to bend and bind. Naturally the angle at which front forks are set
has as much to do with geometric considerations as anything else, so,
as you might expect, they bend, especially on full rebound. Modern
material developments have added another dimension to the nightmare. As
noted above, teles under load tend to bind. Nowadays, thanks to new
wonder Teflon and sundry similar materials, front forks do not bind,
neither do they stick. This is wonderful from the point of view of
constant speed crusing, but any acceleration or, more important,
deceleration, results in appalling front suspension movement. The
energy for this dive comes from the high centre of gravity, which
results from all that weight needed to make the frame stiff, and ...
the riding position.
The safety bicycle then, as it is currently experienced,
suffers from an unnecessarily heavy frame (which is still too flexible)
and front suspension which does none of its jobs well and some really
badly.
Naturally enough, any attempt to hurl some top-heavy,
overpowered safety bicycle into a corner with the front suspension
diving under the weight transfer and twisting under the brake loads
will surely combine with the finite amount of adhesion and the
handlebars dropping out of sight, to have you on your arse in no time
flat. That this may be the result of basic flaws in the machine rather
than some God-given law of biking may seem a bit radical. But the
conventional motorcycle is the only machine, of the many I've tried to
drive too fast, where machine limitations intrude before the operator's
prudence. Conventional motorcycle front suspension is a major
limitation of the controllability of the machine and there is no
solution to this - only alleviation.
When fitted with an engine, the safety bicycle offers more
problems that just inadequate steering and front suspension. The riding
position and the necessity for a heavy frame which starts feet above
the ground inevitably results in a high centre of gravity. With a rider
aboard, all conventional bikes have a high centre of gravity compared
with a typical car.
This has more serious consequences than merely contributing to
dive under braking (and squatting under acceleration). When a bike is
pulled off one footrest and dropped onto the other, when negotiating an
'S' bend or leaving a roundabout for instance, the centre of gravity
has to be moved through an arc. The higher the C of G, the wider the
arc. The time available for this movement is limited by the time
available for the manouevre to be completed, commonly less than two
seconds. In a normal situation, a typical bike and rider will dispose
of several hundred pounds of energy through this point which has to
move feet in seconds. Newton tells us from all three of his laws of
motion, that energy must be used to do this moving and this energy must
be provided. In practice, the motocycle rider provides it by making
steering and power changes, and moving about on the bike. These factors
are limited by tyre adhesion, the amount and type of power available,
and sheer physical strength. It is apparent that the bikes available
today require more energy to move than is usually available in the time
allowed. Thus they must be driven slower through direction changes.
Of course, it's much worse than that. The movement of the C of
G includes a vertical component; the point moves upwards to a high
point, where the bike is upright, and then back down to a low point as
the bike is heeled over. Moving upwards is easier as the reaction to
the movement is downwards, increasing effective weight and thus grip.
As the vertical movement slows and reverses (as the bike 'goes over the
top') the reverse is true; the reaction is upwards and effective weight
and grip are reduced. This makes control changes progressively more
unlikely and the practice develops of putting enough energy into the
initial movement to carry the bike right over to the other side. This
excess energy is felt at the top of the arc as negative weight, and the
bike is lifted off the ground. This effect is normally within the
suspension movement but the intrepid researcher can experiment, if
prepared to die! When the wheels actually come off the ground (usually
rear first) the whole plot starts to rotate about the C of G rather
than the contact patches. The diameter of the ensemble is now the
distance from the rider's head to the bottoms of the wheels rather than
twice that distance and, although unlikely to be symmetrical, the
result (according to the rules regarding conservation of angular
momentum) will be roughly twice the rate of rotation. The rider has
commonly lost control (not to mention touch and sight) of the bike by
this time.
The inevitable weight, and high C of G of a conventional bike
is a serious limitation of its controllability. (They can't be steered
properly either - I always knew the damned things were dangerous.)
Hopefully you will agree with me that it is now necessary to rub out
most of the picture of the conventional motorcycle that intrudes on our
clean sheet. We can, for the time being, allow the rear wheel and the
vague outline of a power train connected to it, to remain. Having
cleared the sheet of most of the remainder, it's now necessary to avoid
the temptation to seize a pencil and begin to fill it in again. Good
design consists not of solving one problem at a time, but of solving as
many problems as possible with as few moves as possible. Before we
start scribbling, let's have a look at the rest of the plot to see if
there are any other basic deficiencies we can avoid at a stroke. As
more problems are defined, so the remaining avenues for escape become
equally defined. Other problems may guide us in filling that frame and
these forks. But that is of course another story.
High-Tech
Royce Creasey
Bike October 1979
LAST MONTH WAS SPENT USING A large rubber on the drawing of a
conventional motorcycle. Hopefully I succeeded in convincing all
youengineering enthusaists it's best to forget anything owing its
origins to the safety bicycle. Possibly a few of the more dedicated
researchers have discovered how easy it is to get at least one of the
wheels off the ground simply by changing direction. I hope it didn't
hurt too much. Now is the time to consider any other problems which
attend the modification of the bicycle into the contemporary 7001b
120mph monster.
There are only two sorts of machines in this world: machines-
that work with stuff, and machines that work with people. A vital
question often overlooked in the design of the latter is 'how do you
people feel about it?' Energy is more usually expended on ensuring that
the machine feels fine. If we accost a passing biker and ask what
physical sensations most commonly attend biking we discover that pain
is at the top of the list. Careful study reveals that the expenditure
of huge sums of money, and a major reduction in rider control, will
result in only minor discomfort. Bikes which have any pretensions to
good handling usually vary from very uncomfortable to excrutiatingly
painful. Improvement is only possible at the expense of other desirable
properties and usually comes down to separating the rider from the
motorcycle with as much rubber as possible. Even those people who
insist that a bit of pain is quite OK should note that discomfort
reduces concentration. Those who need pain for more personal reasons
can surely obtain it more effectively?
As noted last month, the riding position of the conventional
motorcycle is defined by the need to pedal the bicycle from which it
was derived. My memory is quite clear that I first attached an engine
(the amazing Cyclemaster) to my bicycle because pedalling the thing was
so uncomfortable. Clearly, the need to pedal overcame any consideration
of comfort. Bikers thus get it twice. Forced by convention to adopt a
position which was not even originally chosen for comfort, they are
deprived of the justification of being able to pedal. Normal experience
is that all parts of the body in contact with the bike eventually hurt.
Soreness stands alone as the major limitation on how far and how fast a
bike can be ridden. Daily mileages rarely exceed 500 and people can and
do regularly beat that with trucks. Obviously the existing seat and
footrests will have to go, along with the frame and forks (which is
where the handlebars went).
This brings us neatly to the next point. We are left with that
powertrain and its back wheel. Floating in space above all this is a
rider. Now you know and I know that this hapless person is going to end
up in some sort of semi-reclining feet-first position, but let's
pretend that we haven't thought of that yet and look at the reasons for
locating this floating body one way or the other.
Bodies floating in space invariably run into a lot of
atmosphere sooner or later and it's interesting that they generate most
drag falling face down spreadeagled - just like you see in the Smirnoff
ads. Move the arms and legs forward a bit and you're looking at the
frontal area of yet average biker. As the terminal velocity of a hume
is only 120-odd mph you can see how easy it is to generate enough drag
to support your whole weight. This is taken on the arms and explains
why they hurt so much. The machine isn't too keen either; all the drag
represents fuel consumption. It's a free vote on which is the more
serious but I'd really love to hear any engineer justify sore arms and
high fuel consumption in order to adopt a pedalling position on a
machine which doesn't fit pedals.
The solution is simple: the rider is inclined head first - or
feet first. As humans have their eyes fitted at the front, a completely
horizontal position either way is somewhat impractical and, at first
sight, it may not seem to matter which way is chosen. A closer look at
the aerodynamics indicates that this is not the case. A body inclined
forward will tend to generate lift, as do the bodies of those maniacs
who jump off horrifically high ramps wearing skis. This lift is fairly
small - humes don't fly at all well - but when the shape is faired in
to reduce skin drag any lift is accentuated.
You'll note those little pieces of fibreglass nailed onto BMWs
and Mr Sheene's Suzuki which are presumably an attempt to grab back a
bit of download. One thing they certainly do give is drag, which, I
seem to remember, is the reason we started to mess with the riding
position in the first place. If the rider is inclined to the rear, the
tendency to lift is reversed, giving an equally small but much more
useful download which can be faired without fear of lift.
Furthermore, the simplest consideration of bike aerodynamics
will reveal that, next to the rider, the biggest drag generator is the
front wheel. A headfirst rider will almost certainly have his torso
over this wheel, adding body drag to wheel drag. If reclined to the
rear, the whole body hides in the aerodynamic `shadow' of the front
wheel. This will reduce the clothing required to stay alive in that
100mph gale, and that in turn will reduce the overall drag. This may
sound well in theory, but it sounds and feels even better in practice -
check out Quasar fuel consumptions.
Having taken care of painful arms, it's also necessary to look
at the pain felt elsewhere. Between the two great wars this century,
the Germans researched into pilot position in their high performance
gliders. They had a similar aerodynamic problem - the frontal area of
the sitting human - and they tried inclining the body both forwards and
backwards in an attempt to reduce it. It may surprise some to note that
the human body is much more comfortable lying back than forwards. The
backside has better padding and, providing support doesn't interfere
with the operation of the shoulder blades and trapesius muscles, the
whole rear of the torso can be rested against a surface without
affecting body functions. It's also easier to look at the floor than
the ceiling,thus a reclining body can look ahead more easily than a
prone body.
The major mounting point for the body is the pelvis - the
`seat of the pants' is very definitely the centre of balance. The neat
way the torso and legs are attached to this part means that it can only
be fitted into a machine from the rear. Almost the whole front of the
torso is either too delicate to lean on or is concerned with free
movement for essential operations, breathing being a case in point
(who's got a one track mind then?). The attachment points for the major
muscles used by the arms arc on the front of the body, as are the major
muscles used to balance the torso. It is no accident that all the
machines which require delicate control at huge speeds fit the human
controller in this semireclining position, jet fighters and
formula racing cars being cases in point. Motorcycles are the
major exception.
Just in case you are yet to be convinced about the riding
position and you can't be bothered to spend an hour lying on an
inclined surface, first one way up and then the other, to see which
hurts the most, let's ask the machine how it feels about the people. If
there's going to be any attempt at high speed control, the centre of
gravity is going to have to be radically lowered. Not by a couple of
inches, but by at least a foot. Hopefully to somewhere between the
wheel spindles and the top of the wheels. If the rider goes head first,
the upper part of the torso will be over the engine, with enough
clearance to permit engine and rider cooling. Thus a major part of the
weight will be in the worst possible place, high up and above the front
end. This is one of the reasons we rubbed out all that safety bicycle
framework in the beginning. If we recline the rider, the major part of
the bodyweight will be somewhere just above the gearbox, and
the legs, a particularly heavy part of the body, will conveniently run
either side of the engine. The rider's head, being further back, can
actually be higher up without coming out of the aerodynamic shadow of
the front wheel. Such a position goes a long way towards helping the
machine keep its wheels on the ground.
All limits are set to be exceeded of course and an ability to
turn faster with the wheels in contact will simply mean that people
will turn faster. Here's where we can really help the machine. There's
nothing particularly outrageous about the wheels coming off the
ground. Where it all starts to go wrong is when the rider falls off the
bike. This happens because said body is perched somewhat precariously
astride what is effectively a bench. The only thing available to hang
on with are the handlebars which you will note are part of the
steering. Whoops! Bad move there. Even if our intrepid jockey succeeds
in hanging on after bike and backside have lost contact, the resultant
steering movement will almost certainly result in a big shunt. Hanging
onto the steering device in order to stay aboard the machine in general
isn't a terribly good idea. While we've got the rider into a
semi-reclining position we can cure the problem by fitting the pelvis
into a snug bucket seat and providing a couple of good heel rests which
will allow the rider to jam the pelvis into position. This is how it's
done with kart racing and if you think that you wouldn't get thrown out
of the seat of what is after all a four-wheeled vehicle then I suggest
you try it.
By using a correctly shaped seat and heel rests, the arms are
free for the important tasks of steering, drinking beer and all those
other things which make life so interesting. It also means the rider
cannot fall off and it's not exaggeration to say that, even if none of
the other technical problems are dealt with, this single
improvement results-in a transformation of controllability.
To the point where a 7001b 40bhp monster bike, different from its
contemporaries only in having a feet-first riding position (and some
bodywork), is one of the quickest road bikes in existence. Suddenly all
the marginal control areas applicable to four wheel vehicles can be
exploited on two. The things that are normally associated with
motorcycle accidents, with 'falling off', such as wheel-locking
and aviating, breakaway, stand-grounding and so on, become as
interesting as going sideways in a car.
What we shall try and do in this series is exploit all the
advantages available as a result of ditching the safety bicycle. The
Quasar is already frankly outrageous in terms of the things you can get
away with. We can hope, by avoiding the Quasar's conventional forks and
great weight, to produce a device which will take biking into
completely new areas of radical, out of order behaviour. Our motorcycle
drawing is now taking shape. The front wheel can be permitted in
outline and, curving upwards and backwards from it, is a line which
purports to represent the limit of smooth airflow. This line will owe
as much to aesthetics as aerodynamics; my back garden 200mph wind
tunnel is far from complete. Inside this curve, probably with the upper
half of a Bell Star poking through it, lies the rider. The engine lies
between the legs, the torso reclines at an angle which is just upright
enough for the head to fall forwards at a standstill (so that
acceleration and wind pressure hold it up when you're running, see?).
Heels and backside are firmly supported in suitable brackets and only
the hands dangle uncertainly in space. Having ensured that the rider
and the machine are now in a position to relate to each other under all
reasonable and most unreasonable circumstances, all that remains is to
fill in the gaps left by the disappearance of the safety bicycle.
Hang loose kids, this'll take months.
High-Tech
Royce Creasey
Bike November1979
By the end of last months High Tech, the parts of the
safety bicycle most responsible for the limitations inherent in
'modern' motorcycle design had been disposed of. Hopefully, the
reasoning behind adopting a feet-first position has been made clear.
Our design now consists of a rear wheel and a recognisable motorcycle
power train. The front wheel exists in outline; there's the implication
of conventional motorcycle rear suspension in that we can allow some
form of pivoted fork; and the rider resides comfortably in a suitable
bucket mounted somewhere just above the gearbox.
In normal motorcycle design, the next process could loosely be
described as: 'Hey fellas, we got a bicycle, let's slam an engine into
it!' This is the traditional way of doing things and, as described in
the second article of this series, owes its origins to the appearance
of the safety bicycle at about the same time as the internal combustion
engine. Our task is a reversal of the original. We are saying: 'Hey
fellas, we got an engine, let's wrap some sort of two wheeler round
it!' Our previous study reveals that the commonest form of two wheeler,
the safety bicycle, lacks almost all the qualities we require. In any
design exercise it's conventional to solve the most basic problems
first. Our revered ancestors had to produce a convincing design for an
engine; we must come up with a convincing design for a two wheeler. The
rear wheel appears to be satisfactory, and the chassis connecting all
the various parts is simply a structure with a high stiffness reaching
everything needing support. It's clear that the most basic problem is
some means of suspending and steering the front wheel.
The steered weight of this assembly must be as low as
possible, the suspension must definitely not be part of that steered
weight, and finally the movement of the wheel in its suspension must
not introduce any undesirable geometric changes. The reason for rubbing
out all forms of existing motorcycle front suspension will now be clear
- none meet these criteria. Even the 'centre hub' layouts which are
available in limited quantities suffer from complexity and major stress
concentrations in small areas although the steered weight is low.
When one field fails to produce a solution, it's reasonable to
look elsewhere. The motor car for instance. Ever notice how cars don't
have forks for holding the front wheels on? Hmm, interesting,
single-sided suspension no less. Next time you see one of the old
Citroen DS cars, go and have a look at what holds on a front wheel.
just two skinny steel rods, about an inch thick. This car weighs over a
ton, will do over the ton, and strictly between you and me, the Safari
version with an estate body will carry around a ton and a half. I've
never noticed any flex, let alone bending or breaking. Encouraging,
yes? This indicates that it's possible to hold a front wheel onto a
motorcycle from one side without anything too gruesome in the way of
structural members. Then there's the Reliant. Find one and look how
they hold on that front wheel. Quite a shock, innit? I've never heard
of one falling off though.
Obviously these motor cars, with the exception of the Reliant,
have geometry that is unsuitable for a single track vehicle; the
various arms are almost universally mounted on pivots that run along
the car. This means that the wheel moves in and out slightly as it goes
up and down - okay when there's one on the other side as well, but no
good for a bike. The Reliant demonstrates that it's quite possible to
do it with a single arm, kingpin on one end and a pivot across the car
at the other. This arm is simply a piece of square tube with a round
tube welded through it. Unfortunately, such a system alters the
steering geometry as the suspension moves. The Reliant isn't accused of
good handling anyway, but it's right out of order for our demon
handling bike. This single arm is exactly the same as a swing axle,
albeit turned through 90 degrees. The next step in sophistication is a
double arm. This system, with each arm formed as a wishbone, is just
about universal in any car with pretentions to good handling, because,
by altering the angles and lengths of the two wishbones, the geometry
can be made to do just about anything the designer requires.
The DS Citroens use single arms instead of wishbones but the
result is the same. If these arms are turned through 90 degrees, with
enough offset to allow the wheel to be steered, you're looking at my
idea of bike front suspension. Don't accuse me of being original
either. As trailing arms, just such a system was used to hold up the
front of the fearsome, pre-War, Auto-Union Grand Prix cars. With over
600 supercharged horsepower and truck tyres they didn't exactly have a
reputation for good handling, but the suspen sion didn't break either.
As leading arms, you will (if you read the weekly comics) have seen
this very system on the Elf-X racer. The French seem to be taking the
lead in innovative design these days, although it would probably be
true to say that the English are swinging it.
Maybe I'll be able to find a complete unit in a French
scrapyard by the time anyone in this country has seen past the
telescopic fork. This suspension system is so easy that it's tempting
to overlook the big problem - it's not possible to use a conventional
bike frontwheel. Above all because the steering axis must be on the
wheel centre-line, and practical considerations mean that the brake
must be between the axis and the wheel. It's necessary to use a wheel
with a lot of offset, or to use big words, the mounting face of th
wheel must be set off to one side far enough to get the steering axis
and the brake suitably positioned inside it. This is no problem in
itself, plenty of cars use wheels which mount on a face positioned
outside the wheel rim; check out the front wheel drive Triumph range.
Big snag is that it's clearly necessary to use a bike tyre and
hence the wheel size is limited to tyres that are available. Avon make
a 5.00 x 16 inch Roadrunner. It's a big fat mother, designed to cushion
an unsprung rear end, but nevertheless it's a Roadrunner. If experience
with the Quasar is anything to go on we're going to need all the rubber
that can be found. So it's a 16 inch front wheel. Racing practice
indicates that this is an acceptable size, although near the minimum
limit for stability. As the bike will be exceptionally stable anyway,
and I'm not a racer, there shouldn't be too many problems.
The problem has now moved to the area inside the rim. What's
needed is a wheel with enough offset to get all the steering and
stopping bits in and still make it to the bike rim. I must have spent
about a month driving around in my old Thames van looking thoughtfully
at various cars, without finding anything that would make it. I even
considered using the Triumph FWD wheel mentioned above and, having cut
the rim off, drilling it for the spokes necessary to hold the bike rim.
Then one day I looked at the van instead; 15 inch wheels,
plenty of offset, 'cos the well on the 16 inch bike rim nestles neatly
up against the inner rim of the van wheel. Bit of cutting and a touch
of welding and that's the front wheel taken care of. Just in case you
think I'm going to render my Thames immobile by ripping off one wheel,
it should be noted that, due to Ford's excellent policy of not changing
anything which works, the 14 inch wheels off various Zephyrs, late
Consuls and Granadas fit straight on, neatly lowering the van and
producing the possibility of four front ends for real bikes.
While we're considering Ford components, they do a nice disc
brake, caliper and hub that fit this wheel rather well. Unfortunately
these good people are less interested in weight than we bikers must be,
so if the whole shooting match gets used the result would be a front
suspension heavier than the rest of the bike. The wheel itself could
probably be spoked without losing much strength, after all it doesn't
need to be anything like as strong. Given the number of wheels
available in scrapyards all over the UK, and the low unit cost (wivout
a tyre? Oh, thirty bob, guv), a little experimentation would be in
order.
I'm sure engineers everywhere are already in a state of shock
but I'd be quite happy to cut, shut and try it. Steel is very strong
and doesn't break suddenly when there's that much of it. Long term
security can be achieved by the old dodge of spraying it matt black and
watching for signs of the paint flaking.
The problem now moves to the hub. There's a variety of Ford
bits which unsurprisingly fit this Ford wheel. All that's necessary is
to replace them with something the same shape but lighter. At this
point, actual metal cutting becomes necessary, and the first step would
be to replace the steel hub with an alloy one. As the part in question
is basically a tube with internal shoulders for the bearings and an
external flange at each end - one for the wheel and one for the disc -
this does not imply anything too complex. A hefty centre lathe should
be able to handle it easily.
The disc brake assembly was designed to fit inside a 13 inch
car wheel, so it may be possible to tuck it into the wheel a bit more
when there's a 15 inch rim. The critical clearance is the caliper.
I've no hesitation in using the Ford disc and caliper; they are both
big butch units. Possibly a few ounces could be saved by shaving a bit
off both components but brakes need mass to soak up the heat produced
when they are working.
Things slow down a bit when it comes to the `stub axle' which
I shall henceforth refer to as the upright. This is the part which
supports the caliper, picks up the two suspension joints and
mounts the axle on which the hub rotates. It's only upright in one
plane, but that's what this part was called when I was playing with
racing cars so it'll do me.
Ford would naturally select a useful range of steel and run
off a few million forgings. I don't happen to have access to a suitable
forging plant, but naturally there are alternatives. The nicest
way to do it is undoubtedly a magnesium casting, or, if the threat of
undetectable intercrystalline corrosion causing failures at some
unspecifiable time in the future stops you sleeping, the same casting
in aluminium would offer a slightly heavier solution.
Lacking
all these useful foundry type things, I have in mind yet another
method. The axle I obtain by cutting it out of a Ford upright, thus
ensuring that it's the right size for the hub and the right material
and so on. The upright I can have cut out of a piece of steel plate,
about 11/4 inch thick.
The point of interest has now got as far as the actual
suspension joints. Two will do, and the racers would simply go to the
Ampep catalogue and select a neat fabric bearing spherical joint. These
are lovely pieces of machinery costing at least a tenner each, so I
shall go to my nearest Quinton Hazel stockist and score another pair of
Thames van track rod ends for £5.42. Okay, so one's got a left
hand thread but-I guess I can live with that. You'll note that both
joints run into the upright with the tapered pin facing downwards;
this is so that when the joint really wears the spring loading won't
pop it off - the Morris 1000 front wheel fall-off trick fails to excite
me.
The arms which connect this disparate collection of
machinery to the rest of the bike are at first sight somewhat rude.
Until you remember the Reliant and the motorised bicycle. As the ball
joints will be fitted into a tube it will be reasonable to use more of
the same tube, say 11/2 inch T45 in 14 gauge to reach out to the two
square tubes coming from the suspension pivots on the chassis. Said
square tubes will actually be rectangular, deep, perhaps 3 inch and
narrow, probably 11/2 inch again in something butch like 12 gauge.
So that's the front end. I realise that the last thousand
words or so must have come as a bit of a shock after all these articles
meandering pleasantly through the engineering theory of two wheeled
vehicles. Hopefully, by naming names, listing the bits that would
actually do the job, I have made it all somewhat more real. The front
suspension outlined above involves forces passing along other than
straight members - and thus lacks ultimate stiffness -just bear in mind
that the two arms have no joints in them, unlike the telescopic fork,
that they are much shorter, and that the main force line - wheel
spindle to wheel spindle - is much straighter than that of a bicycle.
Next month's step will be to perform a similar service at the
rear end. The rear wheel has always looked pretty much together, but as
we shall discover there's more to hanging the driven wheel than just
providing a 'U' shaped piece of tube; especially when the rider goes
feet first.
High-Tech
Royce Creasey
Bike December 1979
BEFORE I CONTINUE WITH THIS half-serious attempt to design a
real motorcycle, it occurs to me that the time has come to define a
couple of terms. I find `motorised bicycle' and 'Quasar type' a bit of
a mouthful, and difficult to type besides. In future I'll refer to
these two quite different ways of laying out a bike as Feet First (FF)
and Head First (HF). Old nurses' tales say live patients get pushed
around head first while the dead are moved feet first, which
correlation may amuse some, but it would be more relevant to ponder on
which end of your body you prefer to hit a wall with ...
As promised last month, I intend to consider the problem of
mounting a rear wheel in our FF device. Things are simplified because
it isn't necessary to steer the back wheel - in fact it's a good idea
if the rear end is very stiff indeed in any direction except up and
down. The problem is promptly complicated by the necessity to drive the
rear wheel. Unlike the front wheel where HF practice has enshrined a
totally unsuitable system, the rear end of most motorcycles is quite
good, at least in theory. Forks of any type have inherent
disadvantages, mainly in terms of wheel removal, but for this
application a horizontal pivoted fork of some sort is quite adequate.
The serious mass-manufacturer might well think otherwise.
Various examples of singlesided rear suspension, again in cars,
show it's quite feasible. Front and rear wheels become interchangeable
and the rear wheel becomes just as easy to remove. A nice way to do it
would be to use a single magnesium casting, 'L' shaped and tubular in
section, with the swing-arm pivot running down one leg and the wheel
suspended across the end of the other leg. A drive shaft would
conveniently run down the appropriate arm, with its Hookes joint
forming one of the swinging arm bearings.
For someone in my position this is all rather academic. Ring
and pinion sets of a suitable size and ratio for a bike cannot be found
in scrapyards (yet). In any case, the power loss through any form of
bevel gear is significant and the two other means of transmitting drive
are well worth considering. Chains we know only too well. It's probable
that I'll end up using a chain for several reasons: the primary
transmission will almost certainly be by chain, and there does seem to
be a lot of chain drive equipment lying around the room in which I
write. The third system is probably the best all round and it certainly
has the longest pedigree, Yes folks - belts. The modern tooth belt
drive is on the verge of being good enough to do the job of final
drive. It's cheap, wastes few valuable raw materials, and runs without
oil or significant noise. It's also lighter than either of the other
methods. The efficiency of belts and chains in simple mechanical
terms beats any type of geared drive.
As far as the swinging fork is concerned, it matters little
whether a chain or a belt (two belts?) is chosen. The drive sprocket or
pulley has to be on the swing arm pivot to obtain constant tension, and
the belt will require greater width. Consideration of the rear
suspension and the final drive means that the type of power train must
be defined. There are many different ways of doing it, but as I'm
committed to using existing bits wherever possible, it's pretty certain
that some conventional motorcycle power train will be used. That means
some familiar enginegearbox unit, hopefully cheap, with a
reputation for doing the job without too many problems.
This further implies that the distance between the output
sprocket on said powertrain, and the swing arm pivot wilt be greater
than usual. There are two reasons for this. First, as this is an FF
bike, the rider and passenger's butts have to fit in between the
machinery and the rear wheel. Second, as a result of using real
suspension at the front, that wheel moves in a plane much closer to the
vertical than is the case with telescopic forks - thus the motor can be
much closer to the back of the wheel.
Back at the swing arm pivot, we confront a need for a constant
length final drive chain or belt, and a large distance between the
power train output sprocket and pivot which renders constant tension
impossible. We must consider the use of a jack shaft. At first sight
this means another set of bearings, another shaft and two more
sprockets, all unnecessary in pure transmission terms.
Time for a bit of Innovation, We use the swing arm pivot as
the jack shaft. This means we get constant tension on all the chains or
belts and there's an opportunity to alter overall ratios by varying the
size of the two sprockets on the shaft. As a bonus, the swing arm
bearing problem goes as follows - if you use plain bearings they wear
fast. If you use rolling contact bearings (ball, roller, etc) the
limited movement of the spindle is insufficient to run each ball or
roller around the track to the area where the next ball or roller runs.
This results in 'brinnelling' where the track gets worn into a series
of depressions under each ball, or roller, Using the swing arm pivot as
a jack shaft, running on adjustable taper rollers, completely avoids
the problem, as the shaft is rotating all the time and bearing wear
will be normal.
In addition, we have a shaft which has no major oil sealing
problem, and can be used to drive any ancillaries otherwise driven off
the engine. That 390 watt 12 volt alternator for instance, and a
car-type fuel pump to take fuel from the belly tank to the small header
tank just above the carburettor. The law will insist on a speedo, so
that can come off there as well.
Having filled in the machinery involved in the rear end, it is
now appropriate to consider the structure itself. Traditional practice
follows bicycle concepts; start with a fork and add on the other bits.
This results in more weight than necessary and a rather untidy rear
end. As sheet metal will play an important part in this bike it is
reasonable to make the rear fork that way. Apart from the fact that the
chain or belt guard will be an integral part of the structure it will
also be much stiffer in the important twisting direction if it has some
depth at the pivot. Like if part of the mudguard below the pivot was
included in the structure, and some part of the guard above the pivot.
As the structure now extends some way below the pivot it will
make sense to pick up the suspension unit there too. In fact, the
underslung monoshock system like that found in the successful
Godier/Genoid Kawasaki Endurance racer of a couple of seasons back. We
have a gap between the rear of the engine and the swing arm pivot, and
it seems sensible to put the rear strut there. The rocking link which
transfers theload from the horizontal allows any suspension leverage
required, including rising rate. If pivoted on an eccentric, it could
be an easy way of adjusting the suspension for a passenger. Using a
single strut at front and rear has two major advantages. The weight and
the cost are exactly half that of conventional systems. This type of
structure is a prime case of 'form following functioning'. It won't
look anything like a conventional swing arm.
The wheel, however, will look just like a motorcycle rear
wheel. It will probably be the one from what was going to be my Royal
Enfield Bullet PVT racer. It's a nice enough wheel,being equipped with
an alloy hub, a perfectly adequate drum brake and Enfield's rear hub
shock absorber. It's a QD type and all I have to do is fit a 16 inch
rim to match the one up front.
Having described the front and rear suspensions, there's no
alternative now but to find a method of holding them apart that is an
improvement on what Mr. Setright (latterly of these pages) described as
a damn great trellis. Lots of tubes and stuff like that. All you
do-ityourself enthusiasts and any real bike engineers who picked
up his mag by accident will be itching for this arrogant fool Creasey
to put his foot in it with some blatantly unroadworthy device. Don't
hold your breath, place your advance order now!
High-Tech
Royce Creasey
BikeJanuary 1980
THE TIME HAS COME TO CONSIDER THE KEY piece in this strange
jigsaw of components making up my idea of a real (feet first)
motorcycle. The frame, or chassis, no less. It's going to be a sheet
metal, stressed-skin structure, called 'monocoque' by the trendy, and
the 'tub' by those select people who are probably most familiar with
the design, construction and use of such things - car race mechanics.
The latter is by far the easier to type, so it's going to be a tub from
here on in.
There are a number of very good reasons for using this
construction. It's the lightest and stiffest form of structure
available. Stresses are dissipated throughout the entire unit rather
than being concentrated along tubes, and cunning design means that the
various hollow spaces that result can be used to carry all sorts of
fluids and other parts. Construction is extremely simple, and the
material used is available cheaply. It is no accident that modern cars
and aeroplanes, and indeed boats, use this method of construction. Head
First motorcycles lead the world in antique design.
Stressed skin construction is a study of shape. Instead of
attempting to visualise all the stresses involved in a structure and
leading them down a series of straight tubes, which is virtually
impossible in the average structure anyway, the basic unit is a box. A
metal box, a simple cube, is immensely stiff and loads can be led into
it along any edge or corner and immediately fed into the whole
structure. This is of course a gross oversimplification which
hopefully will cause several dozen highly qualified structural
engineers to choke on their tea.
In practice it means that any box structure made of steel
sheet is so strong that it requires sheet so thin that you can poke
screwdrivers through it. As a result, most serious stressed skin
structures are made of light alloy. Race cars usually have a tub made
:)f 18 gauge L72, an alloy in the Dural group with excellent
strength/weight ratio. The outer skin on F1 cars has to be 16 gauge for
impact resistance, while the modern motor car is commonly made of sheet
steel of 20 to 24 gauge. Ford used steel in the tubs of their very
successful GT40 'sports' car, noting in the design evaluation that,
although there would be a weight penalty as a result, the car would be
immensely strong and offer unbeatable protection to the driver.
Another reason for using steel rather than L72 for the tub is
that the latter material, like all the high stress alloys, work
hardens. Any loads fed into an L72 structure, including vibration,
result in a progressive hardening of the material. In addition, the
stuff age hardens; the older it is the harder it is. As a result, old
L72 structures are prone to cracking. This isn't too much of a problem
on race cars where, if a particular tub is lucky enough to avoid being
stuffed into some armco, it's obsolete after three years anyway. In
addition the level of inspection is higher than that achieved on road
vehicles.
I shall follow Ford's philosophy on this one and use steel.
The structure in question is going to be pretty small so the weight
penalty will be insignificant and the resulting structure will be so
strong that it'll follow the suspension arms through the hole in any
given car door with scarcely a ripple. Another advantage is that the
tub can be assembled by welding.
When it comes to the actual shape of the box it's necessary to
consider the rest of the pieces in the jigsaw. The suspension requires
connection at two parallel and transverse arms at the front and one
transverse arm at the rear. A couple of developments from the resulting
box would support the riders and peripherals such as the motor.
Unfortunately the latter object throws_ a spanner right through that
idea. The spanner is the one you use to undo all the interesting and
esoteric things on the sides of motorcycle engines and gearboxes. Gonna
be a bit of a pain if it's all enclosed in a steel box, innit?
Inspection covers large enough to give access to like a timing chest or
a gearbox end cover would weaken the tub.
The mass manufacturer would avoid the entire chassis idea.
Remember that one-piece swing-arm we considered last month? With a
shaft drive and integral oil tank? Well, if it's shaft drive then the
crank will be longitudinal. A neat way with that layout would be to use
an in-line triple, lying with crank down one side, head down the other.
Then the gearbox casing picks up the swing-arm and a suitable extension
on the front of the crankcase picks up the front suspension.
Back in the world of the probable, rather than the merely
possible, we have a large part of the box taken up by the power plant
and its necessary access areas. This can be solved by looking at the
stresses from another viewpoint. All the major loads pass down the
left hand side of the motorcycle. A simple and crude way would be to
use a suitable ISection girder, with everything bolted to its
right-hand side. A similar job can be done with rather less weight if
the tub follows this route and is restricted to the left-hand side of
the bike.
Now you see why we have the front suspension coming into
the wheel from this side. Bear in mind that the overall width of the
front suspension arms could approach 24" (at and above the wheel
spindle height). If we select a narrow engine this is going to give us
plenty of width for a stressed skin spar down one side of the bike. The
only access required on that side is the primary and centre chain, and
possibly the magneto.
Let us then cast about for an available power plant which is
as narrow as possible on the left-hand side ... In my workshop is a
motorcycle. It's an HF type but the power train is unique in its
asymmetry. It all hangs off to the right of the centre-line. Not
counting shafts, it extends to the left of the centreline by
a mere two inches, so there's room for a box up to ten inches wide.
This is it, folks; the power train is gonna be all Velocette.
There is the matter of the primary chaincase, extended on
the FF Venom (Venom Mk IV?) to include the centre chain, but this is a
sheet metal structure so there will be little difficulty in developing
that component into a sheet metal chassis. Modifications to the engine
will be needed to make it work better and to solve difficulties with
mounting holes and chain lines, but I'll deal with them later. The tub
will consist basically of one thick skin which takes the place of the
right-hand engine plate, extended fore and aft to meet the suspension
pick-up points. It will be considerably deeper than the original plate,
especially below the engine.
Above the engine and gearbox it will reach to the height of
the seat. The left-hand engine plate could have an extension to the
rear so that it too meets the swing-arm.
From the large plate on the left the top and bottoms of the
box will extend outwards. The bottom skin will slope upwards at around
50 degrees, the angle of lean at which we are told it's already lost.
The top will be level and provide one of the platforms for the rider's
feet. The outer skin is a little more complex; the chaincase and
magneto access panels must be provided. The answer is to fit
transverse skins above and below the chains, possibly further
stiffened by a box between the chain runs. Resulting upper and lower
boxes will have a fixed outer skin, and some method will have to be
found that allows the traditional oil leak.
The dynamo drive system would get in the way, so will be
transferred to the jackshaft as mentioned last month. On the right-hand
side we need a structure to hold up the other foot and those other
things needed on a motor vehicle: the battery, perhaps the oil tank,
the horns and so on. The most probably;, solution is a simple tubular
triangle picking up on the three suspension shafts by tapered housings
and bolts. Various brackets can be welded to this unit for the rubber
mounts on which all these ancillaries will rest. The tubular
structure will undoubtedly add even more stiffness to the tub,
resulting in a device so stiff that it would be useful for demolishing
high rises.
Then there's this little matter of the power plant. After the
casual way I've dismissed most of the other components, I could fairly
be accused of blatant favouritism if I accepted the Hall Green product
so uncritically. The definition of the chassis meant that the engine
type had to be known and the fact that I have one available is one of
those happy accidents that make life so much fun. As is that unique and
useful asymmetry. What is considerably more useful is that it's a
strong and consistent 500 single, and the next move will hopefully be
to justify the selection.
High-Tech
Royce Creasey
Bike February 1980
Last month, amid a welter of words about box sections,
aerodynamics and ergonomics, I casually let slip that I intended to use
a Velocette power train. It may have also come across that I considered
this a reasonable thing to do. Discussion of the topic last month was
mainly to allow some definition of the chassis, in the same way that we
chose a transmission while considering the rear suspension. Successful
design must include consideration of all related factors. Selection of
a suitable engine, or indeed any other component, can usefully be done
by finding the unit that does the required job most satisfactorily,
with the fewest disadvantages. The job is familiar: the unit must
produce the 40 horses originally defined and be light, compact and
economical. Applicants will score points for simplicity, availability
and cost-effectiveness. There are many power units that would stand a
chance on such basic considerations, but it is necessary to look
deeper.
The layout described so far imposes limitations on engine
proportions in that there must be a clear space for the rider's legs to
move to their two positions (feet up - feet down). This eliminates
transverse crank engines with more than two parallel bores and we need
not consider parallel twins. Opposed-piston, in-line crank engines are
probably unacceptable too, but something like the Guzzi V-twin might
just squeeze in with the rider's shins painfully close to the barrels.
Ideally, only singles, V-twins with transverse cranks and
in-line engines need apply, but there is an adaptation of the in-line
layout that is particularly suitable. Given a free hand and huge
resources, it would be nice to try a triple, laid onto one side with
the crank running down one side of the bike and the heads down the
other. This lines the transmission up nicely and lets the inlet and
exhaust plumbing slip into convenient gaps. The torque reaction would
be generated well off the bike centre line and this should reduce its
effect considerably. It's these secondary advantages that tip the
balance in design decisions.
Having reduced the field to engines that will actually fit,
weight considerations will dispose of all the cast iron car engines
that would otherwise qualify and the field has now become clear enough
actually to name names. The English weren't the only ones who made big
singles, but, given that the Japanese version pretends to be a multi,
we can save time and pain by noting that the Venom has two huge
secondary advantages. As noted last month, it's available (I've got
one) and its shape is uniquely suitable to an amusing chassis solution.
Both Morini and Ducati make neat 500 Vtwins. I would instantly
choose the Pantah for its looks, but both engines are right up to the
minute with belt driven cams and I can't help pausing at the thought of
two desmo heads on the Duke. The bigger Duke Vs are probably acceptable
as well, although their width could be a problem. The power-to-weight
ratio could get embarrassing at such outputs though.
Of the in-line engines, sundry all-alloy car engines do exist,
but, as with all new engines, initial cost is high and, things being
what they are, component life should at least be scrutinised. Two
ail-alloy car engines have been around for some time, however. Both are
British and both produce outputs in the right area. They are the
Reliant 850 and the Imp engine. Of the two, the Imp is much more
interesting, being a Coventry Climax inspired ohc design that in its
time was totally radical. Nowadays, being obsolete, spares are going to
be harder to find and dearer, and surviving examples could be getting a
bit fragile, the long-standing criticism of this motor. The
Reliant is more sensible. A cruder design with much more development
behind it, the standard version seems unbreakable, and God knows I've
tried. Performance equipment is available as a result of the motor's
use by the 750 racing club and there are dealers everywhere. This is an
impressive list of secondary advantages, offset primarily by the need
to make a final drive unit. You could try sweet talking the Quasar
people out of one of theirs, but actual possession of a Reliant power
train would completely clinch the design decision.
Fortunately for the single cylinder route, it also possesses
significant secondary advantages and the Venom's qualifications go even
beyond its asymmetry and availability. Cost effectiveness is the name
of its game. In relative terms I'm quite sure that the Reliant would
cost far less to operate, check out previous words on the subject. But
the Reliant is heavy. If a motorcycle engine is preferred for its
really low weight, narrowness, and nice noises, then the single that
can deliver the goods is better than a twin, or anything more,
delivering the same goods. Big-inch cylinders waste less heat. One
piston generates less friction than many, when the valves and
ancillaries are added up. One of everything adds up to less money than
lots of everything, and less weight. It's the old 'simplicate and add
lightness' syndrome, at one time the rallying cry of innovative
designers, now essentially subversion. Many of the quoted disadvantages
of single cylinders can be (and were) dealt with. Careful design can
render even one power pulse every two revolutions pleasant and
acceptable. The key to it is the assumption that there exists a
together modern big single that will pop out 40 horses rather than its
internals.
White-haired, gap-toothed old bikers may right now be
composing abuse based on the wellknown fact that Venoms only made
34 horses and went bang in a big way at 6,250rpm. Somewhere it may be
mentioned that Velocette were specialists in production expediency -
nothing new got made if an existing bit would fit ... this is the way
forwards. The Venom goes bang because the valves tangle at overlap due
to poor valve control. We'll come to that. In the meantime the valves
are too big anyway, and the combustion chamber is a terrible shape. One
of the a crescent shapes with big valve pockets and the plug tucked
away off to one side. First expedient solution is to slap on the 350
Viper head which allows useful squish bands to be carved out of the
combustion chamber and requires a flat-topped piston to restore a sane
compression ratio. Just assume that such trifles are well within the
grasp of us real bikers. This improves mid-range power, allows 7,000rpm
(a( least), and must make a big difference to combustion efficiency,
giving better consumption and allowing the ignition to be backed off
from its current 38 degrees (!). In addition, I've just discovered
something about that poor valve control. Being expedient, the Venom
just used the nearest camshaft to hand - as it happened, the KTT racing
cam. Not merely the same profile cut onto a different shaft but the
same actual camshaft. Groovy, it was a fine camshaft, no? Only snag is,
to run it in a Venom they had to turn it round but direction of
rotation remains unchanged. Yes, folks, the Venom runs its cam
backwards. This means that, instead of a valve being rammed open at
some rate just below mechanical collapse and then being lowered with
spring assistance gently onto its seat, the opposite occurs. Having
been gently prised open, the valve gear has the cam suddenly vanish
from under it. Eventually it finds its way back into the seat which it
hits like a trip hammer. Just about every one of the strange, nay,
bizarre characteristics of the Venom engine can be traced to this
reversed rotation. I'm trying not to run my motor until I get a
re-profiled cam.
Realists can still point tiredly at the remainder of the power
train, which could reasonably be expected to wilt under the output of a
properly developed Venom engine. However, its use may well allow the
all-up weight of our bolded to stay at the target of 300lb. It's the
vehicle weight rather than power outputs which trash transmissions and
f think that a 30% weight reduction may well compensate for a 15% power
increase.
It may well be that some of you are still unconvinced- Perhaps
you feel that it would be wiser to save for a Reliant than to cut metal
round a Venom. Further persuasion can be found in the future in favour
of the single. One day soon the petrol will stop coming out of the
little round holes in filler hoses. This useful event will require the
use of less energetic and possibly lower `octane' fuels. Running a
Venom on alcohol requires different carburettor jets. Running it on
methane will take another halfan-hour's work to reduce the
compression ratio by any required rate.
The inherent advantages of the single in terms of thermal and
mechanical efficiency will be crucial with such fuels. Selectors of the
Italian Vs, aloof so far, may be discouraged to note that spares from
Italy could be a long time coming without petrol to propel them. When
the time comes to make bits, it's the machines with fewer bits that
score.
In the final analysis, as I may have already demonstrated,
engine choice depends on several finely adjusted secondary
requirements. This is a familiar situation, and bikers in general have
over the past decades spent too much time considering this choice.
Hopefully, you will have noted that, as long as the thing fits and
makes the rear wheel go round, little else really matters.
I agree heartily with such expedient points of view so,
without more ado, we can abandon consideration of the power plant in
order to concentrate on the novel, and thus more interesting,
requirements for what used to be called the `cycle parts' . . . Next
month.
High-Tech
Royce Creasey
Bike March 1980
IT IS NOT IMPOSSIBLE, THOUGH HUGELY improbable, that some
maniac, working at night round the back of a light engineering factory,
has kept pace with this series of articles on modern motorcycles. In
which case, said maniac will be staring at a device which is very close
to being a motor vehicle, on which only sundry minor points, such as
controls, a seat, and some form of steering, have yet to be considered.
Also the aerodynamics, but anyone who had the rest together would
certainly find these details fairly trivial. The temptation then would
be to do a 'quick and dirty' on everything else needed to obtain a set
of number plates and wheel the result out onto the street. This is what
normally happens to English products. The device is sold as soon as it
hits the street to a person who, in the attempt to become an owner,
actually winds up as part of the development team. The situation here
is different and I wouldn't want anyone who has actually got something
on wheels to feel that they should hang around reading about the rest
of the bike if they don't feel like it. On the other hand, anyone who
has gotten any home built set of wheels onto the road already will know
that completing the main components of the machinery is only part of
the battle. Both in terms of time and money, the `cycle parts' tend to
take up a disproportionate amount. In the ca of a clean sheet FF
design, most of these cycle parts will have to start with a clean sheet
too, even though they will do jobs which are completely familiar. You
can see why I was so keen to use as many existing components as
possible for the machinery; time and money saved on the basics will be
needed to complete the details.
Consideration of the plot so far reveals that most of the
machinery is below the top of the tub. Even if a Velo engine is not
used it is probable that the cylinder head will protrude, but apart
from that only the steering needs to be higher and still attached to
the machinery. It will be useful, from the point of view of
accessibility, if any bodywork above the tub is removable as a unit,
and the layout so far makes this possible. At the front the steering
and lights, and hopefully most of the electrics and instrumentation,
can be supported on a bulkhead in sheet metal, which fixes to the front
of the tub. This bulkhead will serve several other purposes. It will
form the basics of the frontal shape. It will also provide crash
protection for the rider. Ideally it would be complete in both these
areas but almost certainly there will also have to be a nose in GRP and
some suitable crash padding, probably expanded foam.
The shape of this bulkhead will be defined by aerodynamic and
ergonomic factors, so wemust look at these first. Any FF motorcycle
will have better aerodynamic qualities than anHF bike, as pointed out
several months ago, because the rider sits in the 'shadow' of the front
wheel, rather than over it. A major advantage of FF bikes is that they
are comfortable, so it can be seen that ergonomics take precedence over
aerodynamics - with no fairing at all the thing will be quicker on a
given power output, but if it ain't comfy there's no point in getting
involved in the exercise anyway. The seat, a major factor in comfort,
can be extended to include the engine cover and the tail section. This
assembly can then be a unit which sits on top of the tub and is
hopefully QD. GRP would seem to be the material to use and the trick in
getting super light, very strong GRP sections is to use just a couple
of layers of fine woven cloth for the skin and fill the resulting shape
with expanded foam. This has the advantage of localising any accident
damage, which can then be re-covered. Bear in mind that the weight of
these parts is all at or above the tops of the wheels, and thus will
tend to raise the centre of gravity - one of the basic problems which
sent us this way originally. There is a temptation to mount this
assembly on rubber to insulate the delicate bod from rude vibrations.
This is OK in moderation but becomes less relevant if all parts of the
machine are not firmly attached to each other.
Consideration of the actual seating position reveals that,
while it is quite easy to arrange for a rider to be supported
comfortably, our hero must also be able to hold the bike up at a
standstill. These jobs require different sets of muscles, which must be
able to move freely. Whilst riding, the legs hold the rider into the
seat by a simple matter of pushing against the heel rests. The torso
will lie back an angle where its weight will hold it into the upper
part of the seat, but upright enough so that the head will fall
forwards. This is accomplished by curving the torso so that the
lower part is fairly horizontal and the head and shoulders are
virtually upright.
Braced into this position by the legs and acceleration, the
rider can exert surprisingly high efforts on some steering device
mounted in front of the chest. At a standstill the rider is effectively
squatting, body weight taken on the seat. Thus the steering device must
be suitable for use in pulling the torso up into this position, and
capable of some use in holding the bike vertical. The seat back will
also assist in this task, though the thighs must remain unsupported so
that they can be moved from one position to the other. The necessary
body movement can be discovered simply by sitting in a chair with a box
for the feet, and moving from the feet-up to feetdown positions.
The muscles in the hips, which are involved in this movement would not
be restricted by the seat sides. Equally important is that the feet,
while suitably supported in the 'up' position can swing down without
catching on the bike. Most important, it should be remembered that this
bike is capable of sliding down the road on its side and a rider's legs
may be thrown out. Or, in lousing up an emergency stop, the machine may
be just dropped. In either case it would be silly if an errant leg was
trapped between bike and road. Thus the side panels should be shaped so
that with the bike on its side there is a suitable gap for any stray
legs.
Where things get really tricky is in the passenger
compartment. You didn't think I was going to suggest going berserk in
this device all alone did you? You may be wondering just where the helI
the pax are going to get fitted, given this bucket seat business. It's
easy - the seat squab is made long enough for two. The seat back can
then be mounted on a pair of slides, such as are used for car seats,
and slid back and forth to suit. It's sensible, while disembowelling a
car seat for the slides, to use one that has a seatback adjustable for
angle to ensure complete comfort.
Careful study of the relevant bits of human anatomy is
required to obtain maximum comfort for two people. With a flat seat
squab a male passenger tends to get his genitals crushed against the
rider's sacrum (that wedge of bone that holds the hips together at the
back). Even females eventually complain, albeit with a somewhat dazed
expression, of a sore pubis (the arch of bone that holds the hips
together at the front). If the passenger seat squab is slightly higher,
this situation is avoided as there is a convenient hollow (the 'small
of the back') just above the sacrum, for the passenger's delicate bits.
If the rear squab is even higher, the passenger's legs may be able to
fit over the top of the rider's hips, allowing them to be tucked in a
bit more. if this process is taken too far the passenger's knees will
foul the rider's arms when turning on lock. Clearly the answer is to
experiment with various relative heights until both parties are sitting
comfortably. Raising the rear seat squab also allows the seat to be
further back before it runs into the rear wheel area, or, conversely,
the rear wheel can be further forward, and the minimum wheelbase
limitation is reduced. The higher centre of gravity when`
carrying! a passenger would reduce performance when two up, but keep
the passenger sane.
The only area so far ignored is the steering. This is because
I am now going to spring an idea which will convince all the bigots
that this is really not a motorcycle. I want to use what amounts to a
steering wheel. Although a false steering head, as used on the Quasar,
would result in a very simple steering linkage of immense stiffness,
the axis of the bars would be wrong from the rider's point of view. As
we have selected a riding position similar to a racing kart, it will be
most comfortable if similar steering arrangements are made.
Conventional bars, moving on a conventional axis, would be
uncomfortable and difficult in the FF position, While a complete wheel
is unnecessary, it is desirable to have the steering axis passing
between the hands to a point somewhere just below the rider's chin. The
linkage required to connect such an axis to the front wheel is less
than perfect, requiring two links and a rocker. Fortunately, we have a
steered weight which is remarkably low, providing no problem in
obtaining sufficient stiffness for precise steering. The wheel
itself will resemble an airliner aileron control, a stretched 'M' shape
rotating about the lower point of the central V. The grips will allow
the thumbs to hook over the cross bars as this is the most natural way
of holding the hands up. Switches and levers will extend from the
central pad for operation by the fingers, but the 'gun button'
positions will serve for horn and dip/flash. Unless of course you are a
traditionalist in which case I suggest connecting one to a centrally
mounted 20mm Aden gun. While I like the twistgrip throttle, I shall
certainly look into a 'trigger finger' type of control, or a twistgrip
operated by only some of the fingers. With no weight to support on the
hands, they are freed for precise control, and thus can operate
delicate controls. A trigger type control, operated by the trigger
finger (logical, like) and a brake lever operated by the remaining
fingers would allow simultaneous throttle and front brake operation. A
last look round the cockpit reveals that no provision has yet been made
for the gearchange. If this is a Venom FF there is no problem, the
gearchange is on the correct side and a direct link to a simple pedal
provides complete control. If it turns out that pedal lifting is
difficult, then two pedals and a simple rocker will provide control. If
a Reliant FF, or perhaps an Imp FF, then the car gearbox will need
converting to positive stop. This is not difficult, and I can do it for
you myself, for a huge fee. But you can almost certainly work it out
yourself for free. Or catch a Quasar and copy that.
FIM regulations, acting as always to stamp out progress, limit
bodywork on racing motorcycles. Basically the bodywork must not extend
above the rider's shoulders at the rear, nor past the front wheel
spindle to the front. The only long term use will be on the race track
so the bodywork may as well be track legal. There is an area over the
back wheel and below the rider's shoulders which can be most usefully
filled with body. It can be made hollow to act as a top box, and if the
top is flat and angled upwards to the rear, it will possibly even
produce a bit of download at a ton plus. Most important, it will add
side area and hence stability in cross-winds. The centre of the area
viewed from the side should be behind the centre of gravity, which will
be somewhere near the middle of the bike if it all works out correctly.
This gives a 'weathercocking' effect; the bike, although tending
to lean out of a wind, will also turn into it - a degree of self
-correction. This part of the body will need a flat section at the rear
for legalisers such as lights and number plates. At the front, the line
of the bulkhead can now be derived from the rider's legs and torso.
Perhaps most effective will be a simple curved slope running from in
front of the rider's hands, angled to throw air over the
shoulders, to just in front of the feet. A small lip around the
outer edges of this slope will ensure clean separation of the air which
hopefully can be persuaded to re-attach itself to the bike somewhere
along the rear body. I like to have my helmet in the airstream -the
Bell Star flies very stably and gives the rider valuable information
about wind speed and direction. Thus in the centre of this slope there
should be a snout, reaching forwards to form a mudguard, and extending
to the rear into a small screen.
The leading edge of this snout is probably the most important
shape on the bike, as at high speed (80+), it defines the behaviour of
the air over the rest of the bike. Experience on F1 cars indicates that
quite a small, sharpedged area can punch a hole big enough to
drive a bike through, the drag produced being higher than that of a
theoretically perfect oval section, but the relative absence of
skin drag over the rest of the bike more than compensates for this. In
addition, the separation of 'smooth' air from the bike will reduce
unwanted aerodynamic effects, and result in higher stability.
The shape of this snout will have to account for disturbance
produced by the front wheel and results will only be achieved by the
usuaI 'try it and see' methods. Small pieces of ally sheet can
be attached for experimentation with tank tape (Gaffa Tape if you are a
media person), but the main point to watch is the side area where any
bodywork forward of the tub should be a vestigial as possible. It
should, be borne in mind that the sort of downloads generated by racing
car body shapes great, for racing cars. A bike has to be stable both
upright and on its door handles, and pretty disturbing when aerodynamic
effects alter with the angle of lean. Probably the best result to aim
for is the smallest feasible frontal area coupled with minimal
aerodynamic effect apart from mild download. Side area should also be
kept minimal, otherwise high speed cornering into a cross wind could be
somewhat alarming. Anyone who actually finds themselves
considering such fine points of the latter stages of design
deserves a pat on the back and a large gin. Most of us mortals will
probably still be trying to get the chains to line up! Since we are now
at a point in the theoretical design where it could be finished by any
'technically literate individual' (to quote IBM), and t have spent
several months ignoring howls of outrage from traditionalists and
any real time FF developments out there, you will be delighted to learn
that this series is now at an end as far as this design exercise is
concerned. Whatever, I certainly enjoyed spending the money!
Of course there's lots more to building bikes than just the
process of manufacture, and next month I intend to take a look at the
commercial, social and political factors which apply to any attempt to
get anything with wheels into production- It's time to pick up the
flamethrower and go looking for fresh herds of sacred cows!
High
Tech
Royce Creasey
Bike April 1980
Over the past few years, as a result of contact with this
august publication, I've found myself riding a number of modern
machines. As you might expect, I've been suitably impressed with
progress in lighting and brakes and, occasionally, I've come across
bikes which actually handle as well as iron-age Velocettes. Biggest
disappointment so far, apart from the fact that nearly all modern bikes
are too heavy, too complex and too expensive, is the poor performance
of contemporary transmissions. It should be understood that I'm not
referring to specifics, such as the ease of operating the gear
pedal and clutch, but the ability of the power train to do the job
required. Indeed, I'm inclined to believe that very few modern bike
manufacturers understand what's required of a transmission.
The main control required is one which causes the rear wheel
to speed up or slow down. This can be done by either changing the
engine speed, and then directly coupling the engine to the rear wheel,
or by maintaining a constant engine speed and altering the method of
delivering its power. Power output can be used either as speed
(engine rpm) or torque, which is to some extent independent of engine
speed.
In the beginning, this was all clear and, as an engine works
more efficiently at constant speed, attention was concentrated on an
infinitely variable transmission. Unfortunately, there's only a
limited number of possibilities that allow this, a fluid drive for
instance, or, more promising, a mechanical system which does not use
steps (pairs of gears typically). The only way of doing this to date is
to use a friction drive, classically the DAF variomatic system with
expanding pulleys. Naturally Rudge thought of this first_
In the early days both fluid transmission and belts capable of
transmitting real power were unavailable; stepped transmissions became
the norm. The engine had to be under the control of the rider and ratio
changing using several pairs of gears became accepted as part of
riding. It's clear from the efforts of our revered ancestors that they
fully appreciated the disadvantages in this system. It has been
calculated that, during a Formula One race at Brands Hatch, a driver
spends ten minutes of the two hour race in neutral. The same comic also
added up the driver's eye blink rate and concluded that a similar
amount of time is spent with the eyes closed!
Fortunately, our revered ancestors accepted the impossibility
of a practical infinitely variable transmission and concentrated on the
equally vital subjective qualities. The central problem is that control
over the performance of the back wheel, in a conventional transmission,
is exercised a very long way from the wheel - as far away as it's
possible to get in fact. To alter wheel speed, the rider alters the
carburettor settings, itself a bad idea which has required decades of
development of just that instrument. The `instruction' has to be
accepted and acted upon by the engine, and then transmitted via the
transmission.
Problems start at the flywheels. In the old days these were
used as the main energy storage device. Heavy flywheels have the
considerable advantage of absorbing power fluctuations, and the
disadvantage of requiring power to accelerate or decelerate. If the
weight is correctly chosen, the inertia of the engine will be slightly
less than the inertia of the bike over the most useful range of engine
speeds. This will lead to closed throttle deceleration where the engine
is slowing the bike down, gently. It also means that gear changing does
not cause the engine to lose all its speed.
Most important, however, is the drag on transmission. It is
vitally necessary, both for subjective comfort and mechanical
integrity, that the vibrations put into the transmission by the engine
and the rear wheel are killed as dead as possible. Otherwise the result
is `surging' and `snatch'. Surging is simply a situation where an
engine power change results in the transmission winding and unwinding
harmonically. It's caused by the various components in the
transmission flexing elastically and in sympathy. Just about any
direct tranmission will do this at some point in its speed/power range.
The old Morris 1000 saloon was famous for it; sufficient surge could be
induced in the early Ford Capri 3 litre to lose control of the car.
Snatch is the reverse case, where the transmission is wound up to the
point where normal flexing can no longer take place and things start to
bend. The result is that the engine runs into an apparently solid
obstruction and various Awful Noises result. The cure is, of
course, the transmission shock absorber, but it ain't quite that
simple. For this damper to work, the natural frequency of the entire
power train must be considered. The degree of flex in the power train
can be depicted as a simple curve of angular deflection against loading
(see Fig 1). It's the flat part of the curve that causes the problem -
it's the free play inherent in any mechanical power train, and it's the
sharpness of the comer (x) which determines how 'snatchy' the resulting
feel is. The transmission shock absorber must match the main curve
without any kinks (Fig 2). The steepness of the curve indicates the
overall stiffness of the power train and to avoid surge this stiffness
should be high. Without doubt the easiest way to achieve this result in
theory is to use a cam type shock absorber, a stiff gearbox with as
little free play as possible and ... chains.
Chains are capable of considerable elastic flexing along a
very consistent curve which at its upper end is close enough to match
the flex curve of the gears and shafts. At its lower end the cam shock
absorber can be readily adjusted to take over down to the point where
there is insufficient load to take up the free play. It will not go
unnoticed that the bikes of old with a reputation for smooth
transmissions use just such a system.
Equally popular, due to cheapness and convenience, is the
rubber shock absorber. Rubber has the main advantage of having no
natural frequency, ffectively killing any vibrations or power surges
which do not fully compress it. Unfortunately, its load/deflection
curve is a straight line and matching it to the chain flex curve is
rather difficult (Fig 3). The resulting kink is usually detectable
although the nature of rubber means that it tends to he gentle. Surging
at some level also tends to occur but snatching can be non-existent if
enough rubber is used.
Look to the 750cc Royal Enfield Interceptor twin for an
example of an extreme rubber damped transmission. Obviously there's a
contradiction between surge and snatch elimination which can only be
avoided by the use of a shock absorber with a performance that varies
under load, like the cam type. Manufacturers generally select a shock
absorber which best suits the use for which the bike is designed. Thus
the Interceptor, trials orientated in its ancestry, is unsnatchable,
but surges well. The Velocette, coming from a long line of road racers,
is just about unsurgable, but can be made to snatch horribly.
The importance of flywheel weight can now be more fully
considered. Imagine a bike, any bike, under full engine deceleration.
All free play will be taken up in a negative direction and, depending
on the flywheel weight, the shock absorber will also be wound up to
some extent. In the case of light flywheels, typical on a contemporary
engine, the engine will be driven almost entirely by the transmission,
especially in the case of a multi with its high engine braking. The
whole power train will be wound up in a negative direction quite
significantly. With a heavy flywheel engine this effect will be
minimal; the engine is driven by the energy stored in the
flywheels, plus a small increment from the transmission, which will
consequently be wound up much less. So far so good. Then the throttle
is opened. The light flywheel multi immediately accelerates, and
reverses the wind-up in the transmission. This can happen very fast and
will result in snatch and surge in the right conditions. The heavy
flywheel engine accelerates more gently and has less angular distance
to reach the same state of positive wind-up. This effect is more
noticeable at higher engine speeds, Thus it can be seen that, given
identical transmissions, a heavy flywheel engine is going to be
smoother and more manageable in power on/power off situations.
Japophiles can quite correctly point out that this is only a problem if
the shock absorber is inadequate; theoretically, some
hydraulically damped device with a couple of turns of controlled
free play could handle all this, but a flywheel is a shock absorber and
a damn sight simpler than any other type. The light flywheel engine is
surely a marketing production, producing lots of exciting racing
type noises and so on. It's been forgotten that the function of
machinery in a bike is to make the rear wheel go round as
controllably as possible.
A further problem occurs in some superbikes. Here we have an
engine so huge that the flywheel must necessarily be similarly immense,
especially when we consider the big twins from Guzzi and BMW. A
situation exists where the weight of the bike is insufficient to change
rapidly the speed of the engine, resulting in locked wheels when
gearchanges are anything but spot on. Added to this is the use of shaft
drive, the stiffest way of transmitting power currently available. I
find it slightly staggering that only in the last couple of years have
BMW started to fit a shock absorber to their transmission.
The current crop of bikes seems to have been designed
virtually without consideration of these problems; the more 'product
orientated' (ie Japanese) a bike is, the worse the transmission seems
to be. I've driven new superbikes with enough snatch and surge in the
tranmission to make me wonder what has broken. Alternatively,
keeping the transmission of my own ageing heap up to an acceptable
standard means continual fine tuning of the chains at least. Neither
strikes me as acceptable.
Fortunately, the solution may be at hand. The advantages of a
transverse crank engine mean that the layout will always be popular,
especially for bikes with moderate power outputs (say up to 45bhp) and
now we have belts. A successful adaptation of the DAF (well OK, Rudge)
variomatic system, coupled with toothed belt final drive, would cure
most of the inherent problems at source. The primary shock absorber
becomes the final drive belt which, although largely nonmetallic,
appears to have the potential of a curved flex/load graph, avoiding the
kink noted in Fig 3.
The infinitely variable transmission means the engine can be
run at its most suitable speed and control over rear wheel performance
takes place in the transmission, closer to the wheel, and thus should
be more precise. In fact, a twistgrip control should be used, leading
to a very similar control feel to a throttle. !'d rather like to try
two twistgrips, one for the transmission ratio and one for the engine
(Honda did this with their prototype 'Juno' scooter of the mid-60s) but
I'm sure that only one would be necessary.
Wonderful, wonderful, I hear you mutter, so it's possible that
some improvement may occur in the transmission stakes in the near
future. What possible relevance has this to my bike? Well, I don't know
about your bike, but mine has a rapidly dying gearbox and the chain
has, as usual, been comprehensively trashed by winter, despite careful
cleaning and lubing, and the idea of replacing all that noisy, highly
imperfect and very expensive stuff with the guts out of a Oaf (check
your local scrapyard) turns me right on.
Did you know that all these nasty gears and shafts and stuff
account for 70 per cent of the noise a modern motorcar makes? In the
case of worn out Velocettes and brand new Kawasakis, it's more like 90
per cent. Toothed belts are almost as efficient as chains, V-belts
slightly less so, but given the elimination of all gears and the
avoidance of the typical worn out, dirty chain situation, the overall
result has to be varying degrees of improvement of noise, cost and
efficiency.
Hmm ...where did I leave that hacksaw?
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