Extending the life of my car brakes.
October 11, 2009 6:51 PM   Subscribe

If I want to extend the life of the brakes on my car, how should I drive the hill close to my house?

My subdivision sits right off a semi-major street. Approaching it from the east, the road is pretty flat, but then there is a 30 degree decline that goes on for about 150 yards, then the road levels out for around 50 yards at which point you'd turn right into the subdivision. If I want to preserve the life of brakes on my car for as long as possible should I (1) coast down the hill to the bottom, then apply the brakes firmly until I get to a safe speed in order to turn into the subdivision or (2) apply the brakes as I go down the hill, let up a little when we hit level ground (maybe even apply the gas a little if I slowed down too much) then brake as normal to take the right turn?

I know there a lots of variables that can affect things, but just in general, what is the best approach?
posted by SoulOnIce to Travel & Transportation (23 answers total) 2 users marked this as a favorite
Use low gear down the hill to maximize engine braking.
posted by Etaoin Shrdlu at 7:11 PM on October 11, 2009

Gear down to first gear and let the engine do the breaking.
Coasting is the worst solution as it places all the burden on the brakes.
posted by Osmanthus at 7:11 PM on October 11, 2009

My train of thought on this one has always been that brake pads are cheap and piston rings aren't, so I usually use the brakes more than engine compression to slow the car. The Car Talk guys are referring to going down a long grade, where continuous use of the brake could cause them to overheat and fade, reducing their effectiveness, which really isn't the case here.

A long gradual application of the brakes is easier on the system than a quick jolt, though.
posted by hwyengr at 7:49 PM on October 11, 2009 [1 favorite]

From the article:
RAY: Just to remind everybody, we said that when you're descending a long, steep hill, you want to avoid "riding" your brakes all the way down because they can overheat and fail.

In your circumstance, you'd just be trading one cheap wear for another expensive wear, by engine braking. Engine braking is strictly back-up measure either to prevent your brake system from failing due to overheating or to help prevent a skid in icy conditions. It's by no-means the preferred method for routinely slowing your vehicle in routine driving. Your brakes are really cheap and easy to replace and I'd be really amazed if living at the bottom of this hill reduced the lifespan of your brakes in any measurable or significant way, to be honest. You'll do more to save your brakes by being a reasonable driver. Speeding, tailgating, and hauling large loads will kill your brakes much faster than your braking habits on this small hill.

But, if I had to pick, I'd do a combination of the two. I wouldn't ride the brakes down the hill, potentially overheating them, nor would I slam on the brakes at the bottom of the hill. I'd hit the brakes once or twice going down the hill, allowing them to cool a little bit between applications, and then brake more firmly at the bottom of the hill.
I don't think this will actually extend the life of your brake pads, however. At best, you'll prevent some overheating or mild disk-warping.
posted by Jon-o at 7:50 PM on October 11, 2009 [1 favorite]

I agree, brake pads are cheap, transmissions, engines and clutches are pricey... use the brakes!
posted by HuronBob at 8:14 PM on October 11, 2009

Apply the brakes moderately starting at the top of the hill and hold your speed around the speed limit going down the hill. Let off the brakes you approach the bottom to gain enough momentum so you don't need to accelerate on the flat, then apply the brakes moderately starting well before the corner, so your turn is smooth and slow. You shouldn't need to brake firmly or use the gas pedal. And signal well before your turn, as a courtesy to drivers following you.
posted by weapons-grade pandemonium at 8:30 PM on October 11, 2009

I would also advise against using engine compression for breaking.

Be aware of your brake pads wearing and replace them. I know (from my own wilder years) it is easy to procrastinate and postpone replacing brake pads, but it is much cheaper to replace the pads than to replace the whole damn breaking apparatus.

I, too, live in a hilly area that gets icy in winter. Not having seen this particular hill or the traffic involved in this scenario, I would slow the car and apply brakes before approaching the descent to the slowest possible safe speed. (And given this is a "semi-major street," as you say, try signaling your intent to turn much earlier than you normally would). Apply brakes gently a couple of times on the downhill. Since you are in the right lane intending to turn right into a residential area, I don't see a reason to feel compelled to approach the decent at maximum speed posted.

(on preview, what w-g pandemonium said.)
posted by at the crossroads at 8:33 PM on October 11, 2009

Downshift, that's what it's there for.

This doesn't put any more wear on the engine and drive train that the opposite (acceleration) does. Why would it, absent any other malfunction ?

Engine braking is strictly back-up measure either to prevent your brake system from failing due to overheating or to help prevent a skid in icy conditions. It's by no-means the preferred method for routinely slowing your vehicle in routine driving.

It's worth pointing out that the manual for both my truck and my wife's car state exactly the opposite.
posted by Pogo_Fuzzybutt at 9:12 PM on October 11, 2009

Engine braking within reason won't hurt the engine.

Brake pads are cheap, but getting the rotors replaced is not. I would engine brake in that situation.
posted by twblalock at 9:14 PM on October 11, 2009

I agree that in general, engine braking is a technique of greatest use for controlling the speed of a vehicle down a long steep grade, while avoiding overheating of the regular brakes. A 30 degree decline is, however, an unusually steep downgrade, especially if you have to deal with it every time you leave and return from your home. The maximum grade for asphalt or concrete roadways in most states is 6 to 8%, with a few mountainous states permitting up to 12% grades, under certain conditions and pavements. A 30 degree incline/decline is a "grade" of 57.7%, so steep that vehicle weight transfer and raw tire adhesion would become the limiting factors in vehicle control; so I think the actual grade is nowhere near that steep.

Nevertheless, if you have to negotiate even an 8% grade, a couple of times a day, it might be best to get into the habit of downshifting to low gear, as you do so, against the days that rain or ice reduces the traction even a bit more. Having your vehicle under good speed control as you negotiate a steep grade is always desireable, particularly if you are going to be making a fairly sharp turn at the bottom of a grade. But you should also be engaging your normal brakes, as you come to the bottom of the hill, to maintain good speed control. If you have ABS brakes, you definitely want them engaged as you come down a steep hill, so that they can provide anti-skid steering effect, if you do lose additional traction in rain, snow, or ice.

One technique that will extend the life of your brakes somewhat, is known as a "Rolls-Royce stop" for having been taught at various chauffeur training programs put on by the Rolls Royce company, and otherwise taught as Feel-Firm-Feather. The idea is to avoid the slight "jerk" that occurs in the last instant of stopping if a car's brakes are held on to a full stop under normal pressure, due to the sudden change between sliding and static friction states at the brake rotor/drum to caliper pad/brake shoe contact point. By learning to lightly release, or "feather," your brakes at the last instant, you'll still stop, but without the slight jerk that otherwise occurs, and in theory, you don't pull particles of your brake pad/shoe lining out as much.

It does seem to work. I generally go 80,000 to 90,000 miles between brake pad replacements, with a 60/40% mix of city/highway driving in normal American sedans (Dodge Intrepid and Chevy Impala) and pickup trucks.
posted by paulsc at 10:24 PM on October 11, 2009

Looking at it just from the physics perspective, you have a fixed amount of potential energy that you have to dissipate from the top of the hill to the bottom of the hill. This is determined by just two things -- the height of the hill and the weight of the car. Add to this some kinetic energy which is determined by the weight of the car and the decrease in speed from the top of the hill to the speed at which you turn the corner at the bottom.

You get rid of this energy by heating your brake pads and rotors which eventually goes into the air. The total heat energy is the same whether you start braking at the top of the hill, all the way down the hill, or just at the bottom of the hill.

So if you have to get rid of all that heat, you want to spread it out over as much time as possible so you don't overheat your brakes or rotors. This allows more time for the heat to go from the brakes into the air. To allow the most time for the heat to spread out, you should start braking as early as possible and lightly as possible so that you have approximately the same brake pressure all the way down the hill and easing up slightly as you get to the corner. You don't want to just coast down the hill and then hit the brakes hard at the bottom because that means all of the heat is injected into the brakes in the last few seconds, leaving less time to spread out into the air so they will get much hotter.

You don't want to have to accelerate again between the hill and the corner because that just puts more energy into the car that the brakes have to remove. You want to brake smoothly all the way from the top of the hill until you turn the corner.

In general, in any braking situation, the earlier you apply the brakes and the lighter you apply the brakes, the lower the peak temperature of the brake pads and rotors.

For long downhill grades, like a mountain pass, you should downshift and use engine braking, but for short grades I agree with Jon-o, brakes are a lot cheaper to fix than automatic transmissions, clutches and throwout bearings.
posted by JackFlash at 11:08 PM on October 11, 2009

So if you have to get rid of all that heat, you want to spread it out over as much time as possible so you don't overheat your brakes or rotors.

Or you can use engine braking, which contrary to many of the opinions expressed above will make your engine parts work less hard than they have to when you're driving up that same hill.

Engine braking dissipates potential and kinetic energy as heat, just as mechanical braking does. But that heat is not a result of sliding friction within the motor; you're not simply transferring wear from your brakes to the guts of the engine. What's actually being heated is the air passing through the mostly-closed throttle body.

What you're effectively doing, with engine braking, is using your engine as a driven pump. It can do this with less stress and heat development than that caused by normal running. While it's being driven by the wheels, it's pumping air through the intake, which is mostly throttled closed, burning a tiny bit of fuel (if you have a naturally aspirated engine) or no fuel (if you have electronic injection) in it and then dumping it out the exhaust. All the resistance you get from engine braking is derived from the difficulty the intake air has in making its way through the throttle, which is mostly closed during such braking.
posted by flabdablet at 3:16 AM on October 12, 2009

When you apply engine braking, you're increasing engine RPM without correspondingly opening the throttle. That creates a greater pressure differential than normal inside the engine and too much of that too often can cause greater oil consumption as you subject things like valve seals to that pressure differential and force them to leak.

Engine braking is fine, in some circumstances. But if you're routinely downshifting to first and operating your engine at 5,000rpm with the throttle closed, you absolutely are wearing components that aren't normally worn to this extent. Keep it moderate. Keep it under 3,000 rpm if you're going to do it all the time.
posted by Jon-o at 5:43 AM on October 12, 2009

But if you're routinely downshifting to first and operating your engine at 5,000rpm with the throttle closed, you absolutely are wearing components that aren't normally worn to this extent

Running an engine at close to redline will wear it, yes. Don't do that. Whether you're engine braking or not, don't use a gear that's too low for your road speed if you care about your motor.

Engine braking is ... by no-means the preferred method for routinely slowing your vehicle in routine driving

It would certainly be the major part of my preferred method for routinely traversing 150 yards of very steep downhill slope.

I'm with paulsc in not believing that this slope is really 30° - hell, the pitch on the roof of my house isn't as steep as that! - but I have certainly seen housing developments with 10% grades on their access roads, and if I lived in one, I would certainly be using engine braking together with gentle brake pedal application to limit top speed to the 35 km/h my little car is comfortable with in first gear, to get safely down it every day.
posted by flabdablet at 6:07 AM on October 12, 2009

We are in agreement.
posted by Jon-o at 6:21 AM on October 12, 2009

I think so, yes.

In fact I do also routinely use engine braking to slow my car down in normal driving - but I don't do that with the downshifting and the overrevving and the killing and hurting. When I don't actually need to be stopping quickly - which is most of the time - I just get off the accelerator pedal early when I'm coming up to an intersection or a red light or some other obstacle, and let the car slow itself down in whatever gear I'm already using at the time.

I recommend this practice to everybody. It saves fuel, it saves wear on your brakes and motor and driveline, it reduces your average driving speed, and it forces you to extend your attention to stuff a little further ahead than perhaps you'd be noticing otherwise, which makes you a safer driver.
posted by flabdablet at 6:38 AM on October 12, 2009

Which is not to say, of course, that I don't use the brakes. Of course I do. I just use them more gently, and later, than most other drivers I've ridden with.

Also seconding paulsc's feel-firm-feather advice. Smooth braking is good braking.
posted by flabdablet at 6:42 AM on October 12, 2009

Which is not to say, of course, that standing on them and exercising the ABS is the wrong thing to do when faced with an unanticipated wombat!
posted by flabdablet at 6:45 AM on October 12, 2009

I'm surprised no one's mentioned this so far, but if you're using engine braking, your brake lights in the back won't come on. No big deal if the drivers behind you are actually paying attention rather than just applying their brakes when they see you use yours, but if you use nothing but engine braking on a semi-major street once or twice a day, every day, it's only a matter of time until you get rear-ended.
posted by echo target at 8:15 AM on October 12, 2009

My train of thought on this one has always been that brake pads are cheap and piston rings aren't

which would be an issue if engine braking caused excessive wear. It doesn't. A quick google search of "site:ford.com engine braking" and "site:toyota.com engine braking" yields press releases about how their new cars make engine braking easier and more automatic. I only looked at the first page of search results, but I didn't find a single instance warning against moderate engine braking.

For a 150 yard decline, use engine braking but don't over-rev, obviously.
posted by malp at 8:44 AM on October 12, 2009

Engine braking (when combined with respect for your clutch - where appropriate - transmission and rev limits when doing so) does not cause any additional wear on an engine than running it under power does. The forces in engine decelleration is not as severe as a petrol/air explosion in any way. I'm very surprised at the people that are stating that it damages engines or increases wear to any significant or even measurable degree.

It doesn't.

It may cause slightly more oil usage over a (very) extended period, but check your oil regularly as you should be doing anyway- that's why you have a dipstick on your engine. The oil usage increase under engine braking, however, is more likely a result of worn rings/valve seals than any kind of cause. Friction is the ONLY cause of wear to these components and on or off power running makes absolutely no difference whatsoever to the supply or lubrication to the moving parts that are critical in this regard - in short, the stated symptoms of extended engine running are purely 'extended life' issues.

Use careful engine braking - keep a good 1000 rpm from your red line and no sudden downshifts - and just lightly touch the brake pedal with small (as Jon-o says) spaced applications to keep the brake lights on and to control the descent. Prolonged braking will increase the chance of fade and make it more likely you won't be able to stop properly at the bottom of the hill.
posted by Brockles at 7:28 AM on October 13, 2009

The other benefit of engine braking in this kind of situation is it leaves 100% of the capacity of your brakes available to actually stop your car. Very useful if a kid runs out in front of your car or something.
posted by Mitheral at 9:35 AM on October 18, 2009

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