by Jon Taylor (August 2002 – revised November 201
Of all the skills needed whilst riding a motorcycle, when all else fails and the unexpected happens, your ability to get rid of speed and lots of it in as short a time span as possible, must rank up there with the best.
OK I hear you say, I did all that when I learnt to ride, I braked from 50Kph in complete control making sure that neither wheel locked, it was no problem at all. Yes, but I bet you’ve never done that from high speed, that is to say 150Kph or more, or when your bike is fully loaded and carrying a pillion, or on a slippery corner! At the last one many of you will be thinking “Is he mad?… You’ll never catch me braking on a wet or slippery bend … that’s total madness!”
But hey, let’s think about it. Do emergencies always happen on flat road surfaces in dry conditions when we are riding alone? No, of course they don’t and to truly know our, and our machine’s capabilities we need to not only practise, practise, and still more practise, but also understand the theory behind what is happening when we brake. No matter how clever you are, your brain is just not capable of learning new very complicated tasks in the middle of a panic situation.
In recent safety campaigns it has been shown that in an impact speed with a vehicle at 70kph the likelihood of survival is 10%, yet at 50kph this rises to 50%, and at 30kph it is 90%. This is surely an incentive if ever there was one to practise our braking skills and that includes in ALL the circumstances you are likely to come across in your everyday riding.
When the need arises you won’t get the chance to practise a few times prior to it, virtually all your concentration will be taken up with the situation itself. It will be hard enough in the time given just to come to a decision as to what action to take, let alone reducing speed sufficiently to avoid serious injury, so unless your braking skills are so well rehearsed beforehand that you can do this instinctively, your chances of survival in the worst case scenario will be down to luck.
So first the theory, let’s have a look at just what exactly happens when we brake.
If you can picture yourself sitting on your machine, an average rider riding a medium sized machine will weigh together about 300Kg distributed more or less 50 / 50 between the front and rear wheels so that each wheel has about 150kg of weight forcing down onto the road surface.
Now, as we apply pressure to the brake(s) we get what is known as weight transference, and it is this that is responsible for making the forks dive on machines fitted with telescopic forks. As the weight is transferred the springs compress thereby encouraging more weight transfer to take place. Weight transfer still occurs with machines fitted with front suspension systems that do not dive (BMW’s Telelever springs to mind) but it is slightly less due to the lack of fork dive.
So if the weight is being transferred to the front, what happens to the rear? Quite obviously the rear wheel will lose some of the weight that it carries, but why should that be a problem? Well, now imagine a canteen type metal and plastic chair. If we go up to that chair when it is empty and give it a push it will skate across the surface of the floor quite easily. Now place a 100kg person in it and try to push it and it’s a different story, it may just be possible to push it but it will take quite a considerable push to do so. But why?
Okay, some of that force will be needed to overcome the increase in mass, but by far the larger amount will be due to the additional grip that is produced by the chair’s friction between it and the floor. The measurement of that grip between the chair and the floor is commonly known as the coefficient of friction. Now, how does this relate to our rider sitting on his/her machine? Well, as the rider starts braking they only have around 150kg of weight on that front tyre, but as the weight starts to transfer forward it soon rises to 200kg and more, and depending on the machine in question, may even approach 300kg.
Now thinking back to our chair with the 100kg person sitting in it, as the weight increases on the front tyre, so does the grip, and we can therefore apply yet more pressure to the lever and correspondingly achieve even more braking force. However, if we apply that same full braking force all at once by grabbing the lever as one might in an emergency, say sufficient to lock a wheel with 175kg of weight on it, before the weight transference has taken place, what will happen? Yes, with only 150kg on it at the time it will lock.
So what we have to do is apply slightly less force initially, that is to say less than that needed to lock a wheel with 150kg of weight on it, and then progressively increase that pressure until we reach the point at which the wheel is on the point of locking, and as stated earlier this could almost be up to 300kg with 100% weight transference. This is sometimes referred to as “lemon-shaped braking”. Confused? Just look at the outline of a lemon, it starts with a shallow curve which progressively becomes steeper until it reaches a maximum and then tapers off as it comes to an end. That’s how your braking pressure should be.
In exactly the same way, the rider should aim to build the pressure PROGRESSIVELY until reaching a maximum and then tailing off as you come to a stop to prevent the forks extending suddenly as you finally come to rest.
For those of you who ever carry pillions, they will be very grateful for you using this progressive technique every time you brake. If you keep having helmets bashing together when braking, you are a prime candidate for practising this!
But what about the rear? Well, obviously if this extra weight is going to the front wheel it is coming from the rear, so in effect the pressure on the rear brake should be reducing as the front increases, but to consciously vary the pressure of the rear inversely proportional to the front is beyond most people’s capability even for the purposes of practicing, so what many people advocate is to just brake lightly on the rear and apply all your concentration to the front, which after all is the brake that’s going to be doing most of the work and is therefore crucial to get absolutely right.
Now let’s add in a few more variables such as carrying a pillion and possibly luggage as well, what effect would that have? Well, as we are starting off with more of the weight on the rear to begin with we can afford to use more rear brake, after all, the rear wheel has a lot more weight on it, possibly twice as much, yet at the front, before weight transfer takes place, the increase in load on the front tyre may be negligible depending on the wheelbase of the machine. However, once weight transfer does take place, a lot of that additional weight will still transfer forward to the front, especially considering that in the case of the pillion that weight is being carried quite high up, and the pressure required on the front lever can be quite considerable once transfer has taken place.
So, how much extra distance do we need for braking if we are carrying a pillion and luggage? Well the answer to that may surprise you. Providing your brakes are capable of stopping the combined load of the rider, pillion and luggage efficiently without fading, your stopping distance should be the same.
Why? Because it’s all down to that coefficient of friction again. More weight overall equals more weight on the tyres and therefore more grip on the road, so the speed at which you decelerate is almost entirely down to the level of grip of the road surface. When reconstructing accidents Police determine the initial speed of a vehicle from the length of the skid marks. It doesn’t matter what the size or weight of the vehicle is, if the wheels are locked they will all stop in the same distance, and that is determined by the coefficient of friction between the tyre and the road surface. (For the purposes of accident reconstruction though this is not used for motorcycles as one can never know what proportion of braking has been applied to each wheel, as unlike a car, it uses two separate braking systems but the physics are effectively the same.)
Now if you actually go out and practise that you may well find that you do in fact take longer to stop, and the most likely reason for this is that you are not compensating for the additional load sufficiently, by increasing the braking force. This only comes with practise!
So, getting back to our rider, they have to apply just sufficient braking force to ensure good initial weight transference and then progressively increase the force on the front to make full use of the additional grip given by the transference of weight. As we’ve seen above, this will vary with the load carried, it will also vary with the level of grip available between the tyre and the road.
Try using that 100kg of braking force on the front brake when riding on ice, or over spilt diesel, or on a wet worn surface, or when banking the machine! The result will be a locked wheel. When you factor all of these variable in it’s a wonder we are ever able to stop the machine at all.
Another factor that affects weight transference, and therefore the braking performance of a machine, is its wheelbase. A SuperSports lightweight 600cc machine will have totally different braking properties to a large touring machine or a Harley Davidson.
The SuperSports 600 will have quite a short wheelbase whereas the large touring machine will have a much longer wheelbase to accommodate the passenger and luggage. Just have a look at the brake discs on the two different types of machine. Despite its light weight the sports bike will have two very large discs on the front and a very small one on the rear anticipating heavy braking from speed with a lot of weight transfer, whereas the tourer will probably have the same or smaller sized brakes on the front (even allowing for its much heavier weight) yet at the rear will have a much larger brake.
The reason for this is all associated with its wheelbase. If you draw an imaginary line from the bottom of the front tyre to the bottom of the rear tyre, then up to the centre of gravity of the machine with the rider on board (usually somewhere around the rear of the petrol tank) and then back down to the bottom of the front tyre, you will see it makes a triangle. Do this for the sports bike and rider and then do it for the tourer and rider. What do you notice? The triangle for the sports bike has a much shorter base and is taller in relation to its base than that of the tourer. Which then is the most stable? Well, I hope you agree it is the tourer, and from that it’s quite easy to see that a sports bike can quite easily achieve 100% weight transfer, whereas this would be almost impossible on a tourer. Hands up who has seen a Gold Wing doing a stoppie? However, one look at the race bikes on television and you will see they regularly use 100% weight transfer, the rear wheel is in the air.
Getting back once more to our rider, not only do they have to factor all the road surface variables into the equation, but also the wheelbase, load carried and braking performance of his/her machine and one last thing mentioned earlier, bank angle.
In the same way as the co-efficient of friction of the surface and the degree of weight transference have an effect on the ultimate braking performance of a machine, so the bank angle does.
Theoretically, if a machine is banked at 45 degrees, the amount of centrifugal force pushing the tyres out is equal to the amount of weight pushing the machine onto the road surface. Exceed that downwards force and the bike starts to slide.
In actual fact a machine, given a grippy road surface and sticky tyres can exceed that angle slightly as the tyres deform and form a small mechanical lock with the road surface which allows a little more than the theoretical 45 degrees. But the important concept to grasp is that as the bike banks over there is less and less grip available for other things such as steering and braking until at around 45 degrees, none is left. If the surface of the road is wet or icy, then maybe as little as a few degrees will start it sliding before any braking or steering is applied.
PUTTING IT INTO PRACTISE
Bearing in mind all of the above, how is any human being ever going to be able to calculate just how much braking can be done at a given time?
Well, we come back to the good old practise, practise, practise bit again!
But if you’ve just practised at one speed on one machine in a flat car park, that’s not going to equip you very well for the real world out there now is it? The only way you can do that is to practise braking in many different situations such as when cornering. Don’t dream of doing this on a busy road, but on a racetrack or a private road somewhere this can be most effective. The important thing is to start very gradually, building up as you go, as you become aware of what the machine wants to do. Racers do this all the time, it’s called practise sessions.
Exactly the same rules apply of starting the braking with sufficient pressure to induce weight transference (depending on bank angle of course) but not enough to induce a slide, and then gradually increasing the pressure. What does the machine do? It tries to stand up and go straight out of the corner so additional steering has to be brought in to ensure the machine holds its line.
This can all be practised at leisure and the skill is then registered into the subconscious for that day which hopefully will never come when you’re coming round a bend and there’s an accident ahead of you that has blocked the road. You have no option but to brake in the middle of the bend, but all that practising you did earlier will be brought into play, and you will hopefully be able to stop. But even if not, you will have reduced your speed sufficiently to greatly increase your chances of walking away.
So get out there and try all the different scenarios you can think of. Enlist the help of a pillion, perhaps your riding pal will go on the back of you while you try and then you can do the same for them. You’ll both be surprised at how quickly you can stop two-up but I guarantee you’ll both also be surprised at just how much weight the rider’s arms take when you have not only your weight but the weight of the pillion behind you as well, something you don’t always expect until you actually start doing it in earnest.
LOCKING THE WHEELS
Following on from this, if you feel confident about it and your bike allows you to, try practising locking the wheels. Start with the rear, find a good level surface away from any other traffic and in a straight line, travelling at about 50kph lock the rear wheel and keep it locked until the machine comes to a complete halt using your butt to control the machine if it slides one way or the other. This may take several attempts, but once learnt this experience will help you to control a rear wheel slide in an emergency situation without you having to consciously think about it.
Likewise, if you feel able, do the same with the front but with a few important differences.
To hold the front wheel locked will almost certainly result in a total loss of control, so instead this time raise the speed to about 70kph and try momentarily grabbing at the front brake (something you would only do for this exercise) and then releasing immediately. A sort of cadence braking action. With the higher speed will come more gyroscopic stability from the rear wheel so that when you momentarily lock the front wheel it will have less effect on the balance of the machine.
In addition, grabbing at the brake, whilst being exactly the opposite of what we would normally wish to do, is the most effective way of locking a wheel due to effective weight transfer not having had the opportunity to have taken place as described earlier.
What you are trying to do here is identify what a locked front wheel feels like. If it is an emergency situation your brain will not have enough time to learn something new, but if it has experienced it before, it should quickly remember what it is and be able to correct it almost immediately. In normal day to day riding though, hopefully the limits of your braking will not be tested, but the benefits of the practise will still be there. Smooth application at first, building up to firm pressure in the middle and then tapering off as you either apply acceleration or come to a complete halt, will ensure that any pillion riders will have an easy time and that the ride will flow more smoothly.
Another aspect of getting the best out of your brakes is how your controls are adjusted. No two people are exactly alike and things like the length of the fingers, size of the hand and muscle strength vary enormously from person to person. However, nearly all large machines nowadays have the facility to adjust the span of the front and rear brakes so making use of this can improve your braking performance overall.
A front brake lever exerts most force when it is parallel to the handlebar, so ideally you should adjust your front brake lever so that the brakes are fully applied when the lever is about 2cm from the throttle. This way you’ll be exerting maximum braking force and thereby control just at the point you need it. With the rear brake you should aim to be able to apply it without having need to either remove your foot from the footrest or having to rotate your foot through a large angle. Again, roughly 1 – 2cm below the sole of the foot should be fine to prevent unintentional application of the brake on bumpy roads but at the same time exerting maximum control over it when in use.
TWO TYPES OF BRAKING
Also, don’t forget that there are two types of braking, use of the brakes as described above but also engine braking. Follow a rider who you know to be very good and I’ll bet that one of the things that impresses you about their ride is that they hardly ever seem to be using the brakes.
Why? Because their planning and observations are at such a level that they have already responded to what is happening ahead and gently rolled off the throttle early enough to have achieved any SLIGHT reduction in speed necessary by means of engine braking.
However, don’t be lulled into thinking that using the gearbox as a brake per se is what is needed, doing this will be more likely to make your ride even less smooth than before. It is quite common for riders who have not yet fully developed their technique to try to emulate the smoothest riders by mistakenly using excessive engine braking rather than having following riders see them showing a brake light to the rear. What they are actually doing is covering up their lack of forward observation and planning with excessive engine braking instead of tackling the problem directly.
Where engine braking can however be used quite effectively is when travelling down steep hills. At this time using a lower gear will just hold the machine back from actually being accelerated down the hill by the force of gravity, then the brakes can be used just to get rid of a little more speed prior to bends or other hazards that may be encountered.
On very slippery surfaces you may find that the rear brake only gives better control than even engine braking depending on your particular machine. Bikes with a lot of engine braking (large capacity singles and twins, particularly if they have fuel injection) can quite easily break traction at the rear in such conditions just by closure of the throttle, sometimes causing the rider to panic when the rear of the machine steps out without them even touching the rear brake.
In these circumstances it can sometimes be best to de-clutch and very lightly apply the rear brake, releasing if the wheel starts to slide again and then gently re-applying the pressure, even better if antilock brakes are fitted as these will do the work for you. The reason for this is that you have a finer and more immediate control over the pressure to the rear brake than you do by controlling the twist grip and this will be even more pronounced with machines fitted with shaft drives due to the torque effect of the drive shaft and what is commonly referred to as shaft-jacking. (The effect of the rear of the machine rising as the power is applied and vice versa)
ANTI-LOCK BRAKES OR ABS
One type of braking system that we haven’t covered yet is antilock brakes or ABS as it is commonly known. This is usually and electro-mechanical system that senses when a wheel is about to lock-up and momentarily reduces the pressure to that brake until grip is regained and then re-applies the braking pressure, all in a fraction of a second and far faster than any rider would ever be able to do.
The real benefit of anti-lock brakes is that they give a rider the confidence to brake hard if the situation requires it without the fear that the wheel might lock-up and the rider lose control. In a study in America it was found that a large number of riders, in an emergency situation, would brake excessively hard with the rear brake and either not use, or use very lightly the front brake for fear of losing control.
Now as we’ve seen earlier, it is the front brake that does most of the stopping when braking hard, and as we’ve also seen, the difference between reducing speed quickly but effectively and not doing so can literally be the difference between life and death. So if the rider has the confidence to squeeze the front brake lever hard, safe in the knowledge that the ABS system will save them, they are far more likely to use it to it’s full potential than if they are frightened of it through lack of experience or practise.
Don’t be fooled though into thinking that ABS will save you every time however. One large problem with ABS on motorcycles (other than Sports ABS equipped machines) is when that machine is banked over. As we’ve seen earlier, ABS senses when a wheel has or is about to lock-up and if you’ve already got a reasonable bank angle on, that momentary locking-up will be enough to start the machine sliding sideways. And it doesn’t matter that the ABS has released the pressure momentarily, because by now the wheel is sliding sideways, and even if they system releases all the pressure there is a good chance that the machine will continue sliding. Result? The wheels slide out from under the machine and the rider loses control.
At the beginning of this chapter we talked about how effective reduction in speed can have a dramatic effect on the outcome if the worse comes to the worse. However, very often in actual situations the wrong decision is taken at an early stage which leads to the situation becoming worse than it needs to be. Take for example that ever-present threat to the motorcyclist, the car pulling out from a side turning.
If the rider hasn’t anticipated this happening by use of the other tools we’ve mentioned to avoid this situation in the first place, they may be faced with making a very quick decision based on the circumstances prevailing at the time, that is to say, do I brake hard and get rid of my speed (the thing that’s going to hurt you) or do I try to take avoiding action by effective use of countersteering?
If it’s the latter, the rider is now committed to a course of action that effectively precludes braking, as the laws of physics prevent a motorcycle from both braking very hard and swerving at the same time. This may be fine if the driver of the emerging car has actually seen you and stopped, but can you afford to take this chance? If they carry on moving you are likely to collide with them only in a slightly different position. If you’ve gone for the front and they carry on, the two of you meet on the other side of the road, if you decide to go for the rear, anticipating that they will carry on pulling out and they stop then you collide with the rear. But the really important concept to grasp here is that on both occasions you will impact with most or all of your original speed.
If by trying to swerve round the front of the car, it takes you into oncoming traffic then you need to add your speed to that of the oncoming traffic and the consequences don’t really need much thinking about.
So, the overwhelming first consideration in any of these situations must be to reduce your speed as quickly as possible whilst retaining control of your machine, most other courses of action are a gamble on what the other road user may or may not do.
Remember, actually running through in your own mind potential scenarios like the ones mentioned here will prepare you mentally to make a quick decision as to your best course of action should that situation present itself in future. It’s almost like gaining the experience without actually having to go through it much in the same way as pilots do in flight simulators.
Once again it all comes down to a combination of the knowledge of the theory behind what is happening to your machine and practise in as many different conditions and scenarios as you can find. If you are fortunate enough to have ABS fitted to your bike, try it out. See what it can, but even more importantly what it can’t do. If the worst ever happens you may be very grateful you did, as it will help your brain come to a very quick decision about which course of action to take.
Hopefully, by using the rest of the bag of tools, your observations and control of speed will never allow you to get into these situations in the first place, but even the very best of riders have been caught out from time to time, so really work on those braking skills and give yourself the best possible chance. If the time ever comes you will thank the day you carried out all that practising, I assure you.