REAR BRAKING


Rear Braking - sliding, and falling

From: Janek Rebalski <janek@motorave.net>
Date: Sat, 30 Oct 1999 12:40:25 -0700

Whether to use front brake only or both:

There is the MSF/DMV official way, then there is the "racer" way, and there is the ABS way. The MSF/DMV way mandates to always use both brakes: when it's dry, when it's wet, when you are going straight, and when you are leaning and turning. The racer way is stay off that rear brake if you want to live, except when it's slippery or when you need to use the rear brake for chassis control under special circumstances. The ABS way: Apply both brakes and keep them applied when ABS kicks in - let ABS do the job of not letting either wheel skid. (Note that ABS will not prevent skidding in corners when leaning - that's when you run out of lateral traction and ABS does not work sideways.)

And now, for anyone who cares about my opinion on the matter.

What happens when you do start to skid? When going straight, the rear wheel lock up results in a skid. The bike automatically compensates for it so you don't need to do anything in the steering department, just keep that rear brake applied and let the wheel skid. If you let go of the brake, you will highside; if you don't, you will likely come to a stop with no more that a rapid heartbeat. If your front wheel starts to skid, immediately get off the front brake. The front wheel lockup will invariably result in a severe headshake and a highside. It appears to me that these are the reasons why MSF/DMV insist on using both brakes: if neither wheel skids, you stop within shorter distance (15% shorter?); if the rear wheel skids, it's relatively easy to stay vertical, even when a person panics and freezes on the controls - which is good in the case of the rear brake (though not good in any other aspect, such as grabbing the bar for your dear life). And when it's wet, your braking is much more effective and you minimize the front wheel skid, which is dangerous and difficult to control for many people.

When you're leaning and braking, what happens when you skid? This is different. The rear wheel skid becomes very dangerous because it's likely to result in a highside. The front wheel skid is now more likely to offer you a lowside as a likely outcome. In a turn, the rear wheel skid is difficult to control, unless you're on the gas and not on the brakes! To recover you will need to stand the bike up, but here is a small problem: you probably don't have much space to go straight with rear wheel skidding. Frankly, you're screwed - or you get lucky. The front wheel skid when you're leaned over is actually easier to control - it does not automatically translate into a headshake and a highside, but will either give you a lowside or you will manage to recover after sliding a bit, propping yourself with your knee puck, and praying heard. So why does MSF/DMV insist that you use both brakes in a corner? Well, they are aware that most people are nowhere near pushing the bike to its limits of traction and lean angle, and consequently that they are more likely to run wide in panic than to actually slide out of the turn. Of course, they recommend that you apply both brakes gently when leaned over as to be able to control bike's natural tendency to stand up and not to initiate a skid in the first place. And if you really need to brake hard, stand it up first and then brake hard. Finally, since you're a licensee of the state and a graduate of the safety course, you obviously will not go too fast and lean too much in corners to begin with - if you do, then it's not their problem anymore - you asked for it and you broke the laws.

Racers: well, their laws are kinda different. They go fast, very fast, and they try to survive at the same time. They got some serious skills on their side. They know that when they hit those front brakes hard, the rear will simply come up and any rear braking will end up being at best ineffective. (They DO use the rear brake - not all of them, but quite a few - but this is for chassis control reasons and not to extract the maximum braking power from the bike.) At worst, the rear wheel will not come up fast enough and it will start fishing around and sliding - under those circumstances you can't continue applying the maximum front brake pressure, because now you got to control that wayward rear. Not only your braking distance has just become much greater than promised, but also you are now sitting on an unstable bike that you can't maneuver anymore except continue dead ahead towards whatever it is you are trying to avoid in the first place. And racers know very well that to fall down is one thing but to impact something is quite another, and they try do their best not to do the latter. Preserving even a modicum of control over where the bike is going is paramount. Front wheel skid? They got sharp reflexes allowing them to release that front brake in time to forestall a headshake. In the corners? Going too wide? There is only one thing they do: lean to the max, skid the rear with the throttle, and if all that doesn't work, then they ARE going too fast (for the line they chose), and go down in a nice lowside, most likely getting up afterward and swearing at the damn tires or something. They also know what happens to the guys that highside after their rear slides and catches on again: ambulance. Ever been watching races? Very educational.

Now, back to the real world, the streets. The same physics apply here as on the race track. So, why should the techniques be so different? A good question. The rear wheel skid is actually much more likely on the streets: there is sand, gravel, oil, wet spots, black ice, mud, leaves, and so on, while the average rider is nowhere near as skilled with the brakes and the throttle as the racers.

Intersections and corners are the worst. If you're going straight and you think that you've got good traction, you may very well be surprised when the rear should suddenly do a dance on you even if you apply a judicious amount of rear brake. But that happens - there is simply not much traction at the rear when you're braking, and pretty much none when you're braking hard. If you're going slow, no problem. If you're going fast, you don't have as much of a margin: a routine quick stop at an intersection turns into an emergency with cages around you. If you're going slow, why worry about the minimum braking distance - just yank the front brake, the rear will lift and you're stopped. When going fast, the last thing you want is the bike out of control. Your hand is much more sensitive and quick than your foot, and if you have proper reflexes and training, you should be able to take care of that possible front slide over some debris on the road and retain control over the direction of travel and leave yourself the option of swerving around an obstacle. If you can't, time for some training on a parking lot.

The curves: I take the real world curves to be the same as those on the race track, except for, once again, all that potential debris as well as the frequent lack of visibility. Wanna highside with that rear wheel skid? I don't. Maximum breaking distance? In a curve? Either you gently brake to control the speed or you stand the bike up and brake hard, in which case the above paragraph applies. Starting to skid in a curve? You better be on the throttle and not on the brake.

Everyone I know agrees that in the case of marginal traction (rain, sleet, sand), one should avail oneself of both the front and the rear brakes. If you don't know how to slide around on a bike on a slippery surface, either park the bike or go slow and try to minimize the chance of having to brake hard. The interesting thing is that it is possible to go too slow: if you slide at a very slow speed, your tires may not have time to go the distance to reach a spot with more traction and you will go down.

My rule of thumb: if I know or think that there is slippery stuff around and ahead, my right foot goes into *gentle* action and my braking becomes progressive and cautious. If I don't think I will be running over some nasty debris, I stay off the rear brake. And I am always more concerned with maintaining control and ability to maneuver around obstacles than with the maximum effectiveness of the brakes. Even with one finger on the front brake I can stop faster than the traffic around me, and I neither want to hit something or be ran down by something.

I don't intend to persuade anyone to do things one way or the other. This is just my perspective on things. If you are a slow and cautious rider, follow the official guidelines. The odds will be in your favor. If you ride fast, you better know what you're doing and why.

Janek


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