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General Knowledge · Mountain Driving

Why can continuous, heavy use of the service brakes on a long downgrade cause the brakes to lose stopping power?

1.Continuous heavy braking builds heat in the linings and drums, reducing the friction that stops the vehicle, a condition called brake fadeCorrect answer
2.Continuous braking drains the air system's stored pressure until the brakes cannot apply any force at all at the wheels, no matter the grade
3.Continuous braking wears down the tire tread, and that loss of tread is what actually causes the loss of stopping power here
4.Continuous braking only causes a problem if the parking brake happens to be engaged at the same time as the service brakes

Explanation

Riding the brakes continuously on a long grade generates heat faster than it can dissipate, and that heat buildup reduces the friction between the brake linings and drums or rotors, a condition known as brake fade that can progress to a real loss of stopping power. 49 CFR 383.111(a)(19)(iii) names proper braking techniques as required knowledge but does not explain the mechanism, so the heat-fade explanation is standard driver-training content, attributed to the manual. The wrong options each substitute a different, unrelated mechanism, air pressure depletion, tire wear, or parking-brake interaction, for the actual cause, which is heat building up faster than the brakes can shed it.

Source: 49 CFR 383.111(a)(19)(iii)

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