Lower Gear vs. Riding the Brakes: What's Best

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driving tips, brakes
Dear Car Talk:

I drive an '09 Ford Explorer Sport Trac. I drive it up and down a very steep mountain road every day -- a 7-degree incline. Every day when I drive down the mountain, I have two options:
  1. Drive with the brakes on all the way down the hill to keep me at a safe speed.
  2. Throw the truck into a lower gear.
Which is better for the vehicle?

-- Joe

The lower gear, Joe.

A 7-degree incline is pretty steep. If you don't believe us, set your treadmill on a 7-degree incline and walk for five minutes.

The primary reason to use a lower gear is safety. When you're riding your brakes for a long period of time, all that friction turns into heat, which can overheat your brakes and cause them to fail. And traveling down the mountain without brakes won't be good for the vehicle either, Joe.

What actually happens is that the brakes get red-hot, and that heats up the brake fluid. Once the brake fluid boils, it's no longer able to transmit hydraulic pressure, and you can't stop the car.

That kind of constant heat also increases the likelihood that your brake discs will warp and need to be replaced. And the truth is, putting the truck in a lower gear when traveling down a steep grade does no harm to anything else.

You're just taking advantage of the natural compression in the engine (the pistons compressing air) and using the transmission to apply that natural engine braking to the wheels. The car will make more noise, because the engine is revving faster. But it's not hurting anything.

Occasional braking is fine. So ideally, you'll find a gear where you're moving fast enough to get home before the ballgame is over, but not gaining so much speed that you have to sit on the brakes constantly. 

So try shifting one gear lower and see how much natural braking you get. If it's not enough, drop down another gear. And if you get down to first gear and you're still not going slowly enough, look for another job.
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driving tips, brakes

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