Driving down a steep hill, which is better: braking or downshifting?

Dear Car Talk

Dear Car Talk | Aug 01, 1992

Dear Tom and Ray:

I live on a mountain. The road from town to my home is steep and winding. Near the top of the mountain is a sign by the side of the road advising trucks to shift to a lower gear. An argument rages between those of us who have passenger cars. Should we also shift to a lower gear and thus use the engine to help slow down the vehicle's progress downward, or should we depend entirely upon the use of the car's brakes? Proponents of the former say that the brakes are less likely to wear out if you downshift, while proponents of the latter say it's better to have wear and tear on the brakes than on the transmission. I am more comfortable shifting down, and still find it necessary at times to supplement this with the brakes. What is your advice?

RAY: Our advice is to keep doing exactly what you're doing, Mary. When you're coming down a long, steep hill, it is not just advisable, but almost imperative that you put the car in a lower gear. When you do that, you use the compression of the engine to slow the car down. That means you don't have to stand on the brakes all the way down the mountain.

TOM: If you constantly ride the brakes down a long, steep hill, there's a real danger that the heat from the friction of the brakes will cause the brake fluid to overheat and even boil. That's very serious, because it can cause complete brake failure.

RAY: So what you're doing is absolutely correct The sign really should advise trucks AND cars to shift to a lower gear. They probably figured that car drivers would be smart enough to figure it out for themselves...but after hearing about your friends, I guess they're going to have to reconsider.

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