161. Why do the front brakes of a bike provide more braking power than the rear brakes, assuming both are applied with equal pressure?
When you apply brakes on a bicycle, you make it harder for the wheels to turn. The ground must then exert backward frictional forces on the wheels to keep them turning and it is these backward frictional forces that slow the bicycle's forward motion. But the forces that the ground exerts on the bottoms of the wheels also produces a torque on the bicycle about its center of mass—the whole bicycle has a tendency to begin rotating. Fortunately, the bicycle rarely actually rotates—if it did, you would fly forward over the front wheel of the bicycle. But this tendency to rotate during braking pushes the bicycle's front wheel downward onto the pavement and lifts the bicycle's back wheel upward off the pavement. The added pressure between the front wheel and the pavement improves traction there and makes the front wheel particularly effective for braking. The loss of pressure between the back wheel and the pavement reduces traction there and makes the back wheel particularly ineffective for braking. In fact, it's easy to begin fishtailing as the rear wheel loses traction completely.