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:
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.
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.
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.
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!
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.
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.
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!
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?