Brakes should be tested on a dry, clean, reasonably smooth, and level roadway. A true test of brake performance cannot be made if the roadway is wet, greasy, or covered with loose dirt so that all the tires do not grip the road equally. Testing will also be adversely affected if the roadway is crowned so as to throw the weight of the car toward the wheels on one side or if the roadway is so rough that the wheels tend to bounce.

Test the brakes at different car speeds with both light and heavy pedal pressure. However, avoid locking the brakes and sliding the tires. Locked brakes and sliding tires do not indicate brake efficiency, since heavily braked but turning wheels will stop the car in less distance than locked brakes. More tire-to-road friction is present with a heavily braked turning tire than with a sliding tire.

The standard brake system is designed and balanced to avoid locking the wheels except at very high deceleration levels. It is designed this way because the shortest stopping distance and the best control is achieved without brake lock-up.

Because of high deceleration capability, a firmer pedal may be felt at higher deceleration levels.

External Conditions That Affect Brake Performance

 

Tires: Tires having unequal contact and grip on road will cause unequal braking. Tires must be equally inflated, identical in size, and the tread pattern of the right and left tires must be approximately equal.

Car Loading:  When a car has unequal loading, the most heavily loaded wheels require more braking power than the others. A heavily loaded car requires more braking effort.

Wheel Alignment: Misalignment of the wheels, particularly in regard to excessive camber and caster, will cause the brakes to pull to one side.