This was originally going to be in response to some other thread about gimping the rear rotor, where demented and slugger were getting ripped trying to explain this, but I see so much misinformation on this I wanted to make it a new one.
Let me start with this. The rear brake is not useless. However, I'm going to attempt to prove that constant pressure on the rear brake throughout deceleration cannot be the fastest method of stopping on any vehicle light enough to do a stoppie (a technical term).
Pitch, or movement forward and back of the chassis, is a direct function of acceleration (meaning change in velocity, speeding up or slowing down) and nothing else. In fact, if you were to only use rear brake, the bike would still pitch forward--that is until the rear wheel came up enough to lose traction and skid, which wouldn't take very long. So if your rear wheel isn't off the ground it might feel nice and comforting mashing on all kinds of brake levers, but you aren't stopping faster. Front brakes on bikes and cars and whatever don't happen to be stronger, they are made stronger because that's where the weight transfers. In fact, if cars were light enough to do stoppies, you would not need rear brakes on them either for straight line stopping. Even if you didn't have a suspension to compress and the rear doesn't lift, the front tire itself would flatten and does, increasing its contact patch while the rear equalizes into it's natural toroidal shape while lifting, providing almost no contact/friction.
Now, there is a case for using the rear brake initially while there's still contact pressure on both tires, and progressively less until the front forks are loaded, which will in fact result in the shortest possible stopping distance. But after that short period your rear tire is in the air (or because of your balance still on the ground but weightless and thus nearly frictionless) and if it's not you are not slowing down as fast. That's is not a debate. Please call your high school physics teacher if this part doesn't make sense. Now let's forget about what brakes we're using for a moment. Both act on the single body that is the motorcycle. Any braking from anywhere has an effect on body pitch. Therefore whatever combination of brakes pitches the bike enough to lift the rear wheel is maximum braking. And what combination of brakes do we use to lift the rear wheel? Anyone? Front, front and more front. If you still insist applying rear brake constantly through deceleration is best please explain how you're able to slow down as fast, or make any angular velocity change quickly, without a pitching or rolling effect. Because this would solve all vehicle dynamics issues, including cars' body roll through turns which engineers have been wrestling with for a 100 years, resulting in variable active suspension and whatever crazy technology.
Let me put it one other way. When drag racing, would you get off the throttle when you feel the front come up so that the bike was securely loaded on both wheels? Of course not! Because then you're not full throttle and accelerating as fast. In fact common drag practice is to balance such that the front is about an inch off the ground through the whole pass. Why, again because pitch is a direct consequence of acceleration and that's where the pitch will be when you are at the maximum.
If nothing else, for ya'll with the "but fast racers do it like this" argument please youtube some Rossi videos, I've seen several shots that show his rear wheel airborn all the way to corner entry. Did he use rear brake when initially loading the front? Or in other special cases? Maybe, but that's it. Unless of course he doesn't like the gyroscopic stability of his rear wheel spinning.
Lastly, all of this doesn't even take into account the dangers in overusing the rear brake, and that most riders out there are not skilled enough, including myself, to properly roll the rear brake for maximum stopping (which people point out is technically the fastest). So I didn't write this to piss anyone off, but really I'm tired of reading about so many crash boom bang stories about people locking up the rear with the good intentions from their MSF instruction, and people still defending it as best practice in an emergency situation. I'd much rather read about someone who dropped their bike after coming to a complete stop untouched using all front brake (who of course got flamed) than someone who slid out the rear at 30mph before they were even close to a car. Is that worth the extra 5, 10% braking when, and only when done perfectly?
So flame this if you want, but it wouldn't make it an argument, it's not.
Let me start with this. The rear brake is not useless. However, I'm going to attempt to prove that constant pressure on the rear brake throughout deceleration cannot be the fastest method of stopping on any vehicle light enough to do a stoppie (a technical term).
Pitch, or movement forward and back of the chassis, is a direct function of acceleration (meaning change in velocity, speeding up or slowing down) and nothing else. In fact, if you were to only use rear brake, the bike would still pitch forward--that is until the rear wheel came up enough to lose traction and skid, which wouldn't take very long. So if your rear wheel isn't off the ground it might feel nice and comforting mashing on all kinds of brake levers, but you aren't stopping faster. Front brakes on bikes and cars and whatever don't happen to be stronger, they are made stronger because that's where the weight transfers. In fact, if cars were light enough to do stoppies, you would not need rear brakes on them either for straight line stopping. Even if you didn't have a suspension to compress and the rear doesn't lift, the front tire itself would flatten and does, increasing its contact patch while the rear equalizes into it's natural toroidal shape while lifting, providing almost no contact/friction.
Now, there is a case for using the rear brake initially while there's still contact pressure on both tires, and progressively less until the front forks are loaded, which will in fact result in the shortest possible stopping distance. But after that short period your rear tire is in the air (or because of your balance still on the ground but weightless and thus nearly frictionless) and if it's not you are not slowing down as fast. That's is not a debate. Please call your high school physics teacher if this part doesn't make sense. Now let's forget about what brakes we're using for a moment. Both act on the single body that is the motorcycle. Any braking from anywhere has an effect on body pitch. Therefore whatever combination of brakes pitches the bike enough to lift the rear wheel is maximum braking. And what combination of brakes do we use to lift the rear wheel? Anyone? Front, front and more front. If you still insist applying rear brake constantly through deceleration is best please explain how you're able to slow down as fast, or make any angular velocity change quickly, without a pitching or rolling effect. Because this would solve all vehicle dynamics issues, including cars' body roll through turns which engineers have been wrestling with for a 100 years, resulting in variable active suspension and whatever crazy technology.
Let me put it one other way. When drag racing, would you get off the throttle when you feel the front come up so that the bike was securely loaded on both wheels? Of course not! Because then you're not full throttle and accelerating as fast. In fact common drag practice is to balance such that the front is about an inch off the ground through the whole pass. Why, again because pitch is a direct consequence of acceleration and that's where the pitch will be when you are at the maximum.
If nothing else, for ya'll with the "but fast racers do it like this" argument please youtube some Rossi videos, I've seen several shots that show his rear wheel airborn all the way to corner entry. Did he use rear brake when initially loading the front? Or in other special cases? Maybe, but that's it. Unless of course he doesn't like the gyroscopic stability of his rear wheel spinning.
Lastly, all of this doesn't even take into account the dangers in overusing the rear brake, and that most riders out there are not skilled enough, including myself, to properly roll the rear brake for maximum stopping (which people point out is technically the fastest). So I didn't write this to piss anyone off, but really I'm tired of reading about so many crash boom bang stories about people locking up the rear with the good intentions from their MSF instruction, and people still defending it as best practice in an emergency situation. I'd much rather read about someone who dropped their bike after coming to a complete stop untouched using all front brake (who of course got flamed) than someone who slid out the rear at 30mph before they were even close to a car. Is that worth the extra 5, 10% braking when, and only when done perfectly?
So flame this if you want, but it wouldn't make it an argument, it's not.
