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Comment by rsync | Hacker News Reader

"We know what those mysterious 1 and 2 labels below Drive represent, and why you engage their services when coasting downhill."

I've never understood this.

That is, I understand completely how people choose to shift into lower gear to lessen their speed gains due to descent down the hill ... I get that.

But what I don't understand is why ? Your brakes are replaceable consumables. Your transmission is an integral mechanical part of the car, the failure of which (in most cases) is synonymous with the failure of the entire car.

So why, given the choice, would you choose to divert wear from the brakes (where it belongs) to the transmission (where you don't want it) ?

Is it just assumed that you won't have decent brakes ?

By the way, I grew up in the mountains in Colorado, and live there part time now, so it's not like I "don't get" the scenario. I get it. This just never made sense to me, unless you assume you've got bad (or poorly maintained) brakes...

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It's not about wear, it's about security and controlling your car... When you're using your brakes you can't control your car nearly as well.

In case of emergency it makes a huge difference. You've got to control your brakes and turn the steering wheel. If you release your foot from the brakes the car will surge forward as it is not limited by the transmission.

Plus water, snow or ice downhill with brakes = danger, very easy to lose control of the car. Again if you're limited by the transmission it's a non- issue.

Plus it makes your brakes hot, which makes them less efficient in case of emergency (I think).

Your transmission should always be the limiting factor of your speed, period. That's it's job, to determine the speed of the car. The brakes are only here for when you couldn't downshift fast enough and you're going to hit something if you don't stop the car. That's what my instructor taught me, and repeated again and again.

When driving I sometimes see people braking all over the place, most of the time they also have strange trajectories, and are not easily predictable. I pass them as soon as I can.

And yes I use a stick, never used an automatic in my whole life in fact. I don't think it teaches you anything about the mechanics of the car as i know mostly nothing about that. But I'm pretty sure you "feel" the car much more. I'm nearly certain the aforementioned brakers are mostly automatic drivers (pretty rare in my country as most people despise automatics.)

No one seems to be answering the question correctly, so here goes:

On a long descent, excessive use of the brakes can cause them to overheat and "fade", meaning that you will not be able to stop the vehicle at the bottom of the hill. This can be caused by loss of friction from overheated brake pad material and rotors, or by the actual brake fluid itself boiling out of the master cylinder and becoming compressible.

This is not nearly as prevalent as it used to be, now that vented disc brakes are standard on most modern vehicles.

See http://en.wikipedia.org/wiki/Brake_fade

Another reason is that fuel injection is cut completely in modern fuel-injected vehicles under compression braking, meaning you will get better gas mileage if you engine brake than if you idle down the hill.

If your car has not ABS, you can slow-down without losing directional control by using the engine. In a slippery slope, if your wheels block (because of braking) you lose the ability to turn to avoid obstacles.

Before ABS brakes were ubiquitous this was more important advice. Most cars with ABS standard advise against engine braking in the manual.

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