Braking acts to stop the front tire. Friction acts at the contact patch under the front wheel to introduce a vector force directed towards the back of the bike. Since the force is not directed through the center of mass of the motorcycle/rider system, it introduces a moment or torque that acts to rotate the motorcycle and rider such that the back tire begins to come off the ground, or reduces the force conducted through the rear tire caused by the weight of the bike. The available braking or frictional force at the read tire is proportional to the weight force directed through the rear tire.

So as the vehicle is braked, available braking power at the rear tire is reduced with positive feedback.

As the vehicle is braked, available braking power at the front tire is reduced with positive feedback, for some given constant acceleration.

An analogy to running is that if you attempt to stop on a dime, you will fall on your face.

Braking acts to stop the front tire. Friction acts at the contact patch under the front wheel to introduce a vector force directed towards the back of the bike. Since the force is not directed through the center of mass of the motorcycle/rider system, it introduces a moment or torque that acts to rotate the motorcycle and rider such that the back tire begins to come off the ground, or reduces the force conducted through the rear tire caused by the weight of the bike. The available braking or frictional force at the rear tire is proportional to the weight force directed through the rear tire.

So as the vehicle is braked, available braking power at the rear tire is reduced with positive feedback.

As the vehicle is braked, available braking power at the front tire is increased with positive feedback, for some given constant acceleration.

An analogy to running is that if you attempt to stop on a dime, you will fall on your face.