Car vs Sportbike braking

[magilson]

I messed up the transfer and lost the discussion; and no it\'s not a \"coinsidence\". I\'d fully like to keep this discussion.

Glen and THM3 say that bikes and cars stop about the same or the bikes do worse. Glen said E46 M3 does a 112\' stop when a YZR R1 does it in 113\'. 70-0? 60-0? whatever.

I say its because of the driver, not the machine. The bike (after some admittedly speculative and simply calculation) the bike roughly has to stop the inertia of 2 lbs of mass while a car such as the new GTI has to stop 5 lbs of mass at a given inertia.

My point I was trying to make was not that a given car can stop faster than a bike, I could whip out the stats on a Formula car and say, tada, I\'m playing out the worst possible scenario, being that I feel my car was the heaviest on the last cruise if not tied with the other MkIV on the run. Since planning for the worst is what you do, I\'m saying the car will do worse.

As Linda Richmand so adequetly put,\"discuss...\"

[Digital K]

how much does the MUCH higher area of tire on the road in a car have to do with braking? cycles dont have shit for a contact patch...

[magilson]

In straight up Newtonian physics the answer would be none actually. I reality when you do a much more in depth analysis it does matter. As I had said in my other posts you have to consider the two types of friction. Static and Dynamic. Static friction is the coefficient used when two object are moving across each other with no ralitive motion. Dynamic friction is the friction of the object as it is moving while moving over the other object and any combination there of. So in nuetral you are feeling (other than wind resistance and simple drive train friction) the dynamic friction of the tire.

When a biker slams on their brakes (hopefully a combination of the front and back) they create a moment (a force acting to cause rotation about a point) in this case the bikes front axle. That\'s why every time I hear someone say the car \"transfers\" weight I want to punch them in the face. It\'s such a poor description of what is happening and the description doesn\'t lend itself to the understanding of what is truely happening and therefore a good way to handle it. All you are doing when that happens is cause a rotational force about your front wheels and the force is coming from your center of gravity.

So when a biker does this it lifts the rear tire a little. Less normal force on the rear tire means less traction and it becomes obvious then that you will not be able to break as strongly in the rear because you will lock the rear tire and move it from dynamic to static friction which is less desireable and more difficult to control. However it in turn makes the front tire that much more effective, which is why all bikers know that the front brakes are the only way to stop quickly. So them it becomes a balance of flipping over vs. stopping fast.

The reason I\'ve gone to all this trouble is because my buddy has a GSXR-750, and there\'s no way it takes him longer to brake than a car, we\'ve all gone driving with him. However that bike is less than stock and his mods help. All in all I don\'t care how \"pro\" the brake squeezers are, they still can\'t be doing it optimally because every piece of physics just screams that the bike should stop faster. I still blame the operator.

[OptimusGlen]

hmm, valid points captian einstein :P but you do have to realize you\'re comparing a GSXR motorcycle (shares braking system with GSXR 1000 I\'m pretty sure) which... is like a Honda NSX-R, in terms of where it sits on the food chain. I compared the R1 to the M3 because they\'re at about the same place on their relative food chains.

Sure, a high end bike is engineered to brake like mad, in the same way a high end car is. Now, take something along the same lines as your GTI, like an SV650 maybe, and you\'ll get different numbers.

I did find the stats for the R1/R6, which is almost exactly what an E46 M3 is. Both from 60-0.



So when a biker does this it lifts the rear tire a little. Less normal force on the rear tire means less traction and it becomes obvious then that you will not be able to break as strongly in the rear because you will lock the rear tire and move it from dynamic to static friction which is less desireable and more difficult to control. However it in turn makes the front tire that much more effective

This is what I\'m getting at. Imagine having all the weight pushing down on the front tire as a motorcycycle stops, times a million for the weight of a car, times 1000 for the traction patch keeping the tires from locking up, plus ABS technology to keep the tires from locking up, plus a massive amount of weight out back to make sure the car doesn\'t flip over on it\'s face, and you\'ll see why cars can and do stop faster than bikes. (obviously not all the time)

Also take into consideration that most bikes on the road are not \"Gixxers\" or R1\'s. Most of the time they have brakes that are a long way off of the high end systems.

Post edited by: OptimusGlen, at: 2006/06/27 23:38

[magilson]

I see what you mean. My perspective is off on the GSXR compared to regular bikes I suppose. It\'s also why good bikes have dual rotors on the front... Also, bike ABS blows. It\'s a nice idea for big fat harleys but on a sport bike its just not going to work good enough until they add accelerometers to help it decide what to do.

I will retract my statement that bikes are automatically better at braking. The bikes I\'ve dealt with are, but apparently not many people around here own that level of bike.