Originally Posted by cyccommute

Bicycling Science by David Wilson. The numbers he gives are a maximum of 0.56g before pitch over on a single bike (tandems can decelerate much more and cannot pitch over). However, I would argue that the maximum deceleration occurs long before you reach the point where downward force is zero. At the point where downward force equals zero on the rear wheel, you gone past the point of maximum deceleration.

Consider: At maximum deceleration, the front wheel is providing 80 to 90% of the deceleration, or roughly 0.45g to 0.5g, and the rear is providing 10 to 20%, or 0.11 to 0.06g. If the downward force on the rear wheel goes to 0, the rear wheel is no longer contributing the 10 to 20% and it's deceleration drops to 0 g. The front wheel is only contributing 0.5g so you've lost deceleration ability. Keeping the rear wheel in contact with the ground, i.e. not skidding, doesn't zero out the rear wheel. You approach an asymptotic limit just before the downward force on the rear wheel reaches zero. Go past that asymptote and you've lost braking power.

It works the same whether or not the bike is a road bike on flat level ground or a mountain bike on a steep pitch.

Please note that I have not said that you shouldn't use your front brake. Nor have I said that your front brake doesn't provide your primary stopping force...on any vehicle. However, relying on only one brake in any situation is not going to provide you with the best deceleration your bike can give you. Relying completely on the rear, as in a coaster brake, give only marginal braking ability. Relying completely on the front just doesn't squeeze out the maximum stopping power of the bike.