Originally Posted by cyccommute

To stop fast in an emergency situation requires more than just practice with the front brake. While it is true that the maximum deceleration you can achieve on a bicycle can be done with the front brake alone, you have to be in a situation that most people wouldn't want to find themselves in to achieve it. Maximum deceleration on a bicycle occurs at the point where the bike is going to rotate around the front axle, i.e. at the point where the bike is about to endo. That's not the point where the rear wheel skids or when it leaves the ground but at the balance point between stopping the bike with the tire or with your face That's not something that most people want to do in order to achieve maximum deceleration.

As long as the rear wheel is still in contact with the ground, the rear brake contributes some amount to the deceleration. It can be a small fraction or more than 20%. How much it contributes depends on the rider's position and the location of the center of gravity. A small shift in the center of gravity can cause a huge change in the deceleration of the bicycle. A much more effective way to achieve better braking would be to practice moving back and down while using both brakes. Practice that to achieve a reasonable method of stopping fast in an emergency situation.