# Say we're driving a bike and suddenly hold the brakes?

It's easy for me to imagine that if we brake the front wheel then there is a chance that I'll flip.

On the other hand if I brake the back wheel, there is no way it'll happen no matter how fast I brake.

But whether I brake the front wheel or back wheel, the force I've added is a backward force at the bottom of the wheel.

So why the different outcome?

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One force goes "inward", the other "outward" from the CoG. – Ignacio Vazquez-Abrams May 28 '12 at 5:24
Hmm... it's hard to express this without pictures. I am sure you can imagine right? Or perhaps the break at the back wheel only applies when the backwheel touch the ground. – Jim Thio May 28 '12 at 8:32

The torque is in the same direction in either case, so the torque wants to lift the back-wheel and flip you over the front whichever wheel you brake with, but when the braking is on the back-wheel, if you lift the back-wheel, the braking force goes away, so the torque goes away. This means that a brake applied to the back-wheel will never be enough (unless it is applied extremely suddenly) to flip the bike, it will just lift the back wheel and reduce the braking to zero, or else make a bouncing back-wheel.

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This is what I suspected. However, as you said your self, what about if the break is so sudden? I feel as if there is something more to this. Anyway, +1 definitely. – Jim Thio May 28 '12 at 8:33