Take the 2-minute tour ×
Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. It's 100% free, no registration required.

Possible Duplicate:
Does Downshifting (Engine Braking) Cause Extra Wear and Tear?

Since the days of taking drivers ed (many years back). I was told that when you encounter a steep or extended downgrade, to conserve your brakes and help increase braking performance it's a good idea to shift from Drive to 2nd (at least on automatic transmissions which is all I've driven).

Still, while the advice seemes valid and for the most part it's helped greatly every so often in winter on hilly areas, on a recent trip through upstate New York, I encountered numerous rural hills so steep and long that when I downshifted, I was hitting 3-3.5k RPM peaking at 4k even as I was doing 40mph and breaking heavily (but steadily) to keep the RPMs in check.

Anyway my main question is that when you see those hills with the signs indicating trucks must downshift, is it also a good idea for people driving sedans and other non-commercial vehicles?

The main reason I ask is because I've heard downshifting saves brake pads but can damage the transmision, so the rationale is to avoid downshifting when possible. I've done this for much of my average driving however I definately would love to get a more solid opinion.

share

marked as duplicate by Bob Cross Jun 8 '12 at 17:59

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

4 Answers 4

up vote 11 down vote accepted

tl,dr: The short answer is no, with caveats.

The longer answer starts with "well, you can kill your car with anything if you try hard enough."

Let's use specific examples of when you should use your transmission for engine braking: Waimea Canyon or Mount Washington. In either case, you are descending thousands of vertical feet at significant grades. If you were to ride your brakes the entire way down, it's highly likely that the brakes would overheat and become less and less effective until they were essentially useless.

This would be followed by a loud crashing sound.

In fact, at the Mount Washington Auto Road, they will not let you proceed up or down the hill unless you are in "2" on an automatic transmission vehicle.

Caveat: when you intentionally put your car in a lower gear and drive down a steep grade, you are giving gravity control of your engine revs. As I say, it is sometimes important to use engine braking (we've discussed the benefits to fuel economy before). However, you are the driver of the vehicle so you have to make the call about how much is too much.

A simple rule of thumb: the redline is still the redline. If your engine braking is pushing the limits of the rated engine speed, it's time to use the brake pedal and slow down significantly and, possibly, drop down another gear. Otherwise, you're going to break your engine in an effort to save your brake pads.

share
    
Thanks very much for the excellent examples! As I'm used to minor hills (with some treacherous Winter icing) typically ddrivers here decide their styles, although knowing that some states require passenger cars to do it, really busts the myth I was seeing on some mechanic website copy (which seemed horribly generic in all cases). –  theonlylos Aug 17 '11 at 3:25
1  
@theonlylos, you're welcome. I highly recommend both the Waimea Canyon and Mount Washington drives. Both very interesting in a variety of different ways. Drive carefully, though.... –  Bob Cross Aug 17 '11 at 3:55
    
If you do this a lot, make sure you check the oil more frequently as well. I've found that my cars use more oil if I use engine braking. Not sure why, but guessing that the vacuum is sucking more of it past the rings, where it will then get burned? –  Brian Knoblauch Sep 23 '11 at 12:19

There are some long 1 in 10 grades in Scotland where the advice for all drivers is to choose a low gear to avoid brake fade, as @BobCross points out.

There are slight differences between automatic and manual transmission cars, though - as you do get more control of revs with a manual, so make sure if driving an automatic that you change into 2 before the slope commences.

share
    
strongly agree on the point of "gear down early and carefully." It's very important for people who haven't tried this to note that gearing down is similar to hitting the brakes but only on the driven wheels. So if you are in a front wheel drive car hitting a downhill turn at high speed, gearing down is going to brake those front wheels less smoothly than the brake pedal. Hopefully, you won't understeer off the road.... –  Bob Cross Aug 17 '11 at 12:32

I have a 1992 Honda Accord auto transmission with 333,000 miles. I have always downshifted one or two gears to save the brakes and avoid excessive speeds on downhill stretches. I often drive in areas with long hills, sometimes quite steep hills. Also often in flat urban driving will downshift a gear to let the car slow down when approaching a red light.

I have NEVER had transmission problems and have NEVER had any issue that required transmission work.

My mechanic agrees with my driving. His only caution is to do the downshift on hills early by planning ahead, and not to do it when doing so would approach the red line.

I have asked Honda about this question, but find it impossible to get any response from them.

share

Great answers above, but as a general comment: if your going down a long steep hill and you don't do it that often (or if you're not familiar with the area) always use engine braking. You can fix a transmission if you somehow screw things up, but you're still much better of than if your brakes overheat and fail and you end up in an accident.

share
    
Very true. Even in suburban areas like where I live, one of the towns actually is essentially all hills and slopes and with a early childcare school being in that whole area, that is defiantly the case with myself and most of the people who live there (especially in the Winter) –  theonlylos Sep 26 '11 at 19:47

This site is currently not accepting new answers.

Not the answer you're looking for? Browse other questions tagged .