Reader Question: Coasting?

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Here’s the latest reader question, along with my reply!

Nasir asks: Hope you are doing well. Currently am doing a bit of traveling around the UK, and in the Lake District in Cumbria, and had a driving related question – couldn’t think of a better person to ask. Around here, there area a lot of bendy and hilly roads, some with steep gradients. One thing I see before the slopes is a sign saying “high gradient, keep in low gear” (or something of the sort). I however tend to hold the brake, and when/if it starts to stall just push the clutch, or if long enough downhill put it into neutral and control speed via the brake. That said, one thing I remember always being told by my driving instructor when giving the UK driving test is that this is “illegal” as it is “unsafe.” I however find that it tends to put less strain on the drivetrain instead of holding it in gear. Fine, granted I probably don’t have the best driving habits (as I learnt, let’s say unorthodox way before I moved to the UK)…. but I can’t think of how this is actually “unsafe.” Maybe, back in the day when brakes weren’t that good, and engine braking was needed; fine, but with modern cars with power brakes well they will hold on anything. Or if you hold the clutch too long it can wear, but why not just put it into neutral?

What are your thoughts on this?

My reply: “Coasting” – disengaging the drivetrain by placing an automatic in neutral or holding the clutch in while the vehicle’s rolling – is supposed to be dangerous because of the increased chance of a vehicle overspeeding and the driver losing control.

Personally, I don’t see it – unless (as you’ve already guessed) the car has really weak brakes and they get too hot and fade. It’s possible, certainly – but probably not unless the car is really old (cars made before the ’90s sometimes did have weak – or rather – marginal – brakes) and you’re descending a steep grade.

In my experience – extensive – you have to be really working any late-model car to get the brakes hot enough for fade to become a issue. Mere coasting probably won’t do it. I’ve only succeeded in doing it when I’m running the car as one would on a race track; decelerating hard from high speed, accelerating to high speed – repeat. Many times. Do that – and, yeah, the brakes will get hot and if they’re not meant for that sort of abuse, they’ll get too hot and then you may have an issue…

But otherwise? I doubt it.

Interestingly, several new cars have a “coasting” (or “sail”) feature that works on the same general principle. The car’s engine is automatically turned off during light load conditions to save microcosmic quantities of fuel.

In the situation you’re describing, you may save a little gas – at the cost of more rapid brake wear, from having to ride the brakes to keep the vehicle’s speed in check while going downhill. Brake pads, calipers and rotors cost more than a little bit of gas, so . . .

My personal practice is to downshift (if the car has a manual transmission) to whatever gear is needed to maintain my speed on a descent without having to ride the brakes; you can do the same thing with most late-model automatics by disengaging the OD or (if it has manual gear selection capability) notch down one or two gears. Of course, if it’s automatic, it ought to do all that . . . automatically!

But, some automatics aren’t programmed that well; and some are programmed to upshift (for economy) and that can be unsettling when descending a steep grade. In that case, manually shift the transmission into a lower range for the engine braking effect.

. . .

Got a question about cars – or anything else? Click on the “ask Eric” link and send ’em in!

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3 COMMENTS

  1. Thanks Eric, guys. Agreed, best to keep in gear – Normally not too bothered with the gas, but the challenge is sometimes, say coming down a bendy road, where you start in gear, but then have to slow down much more than anticipated, say a sharp bend, and then instead of down gearing to the right one just take it out of gear and hold it with the brakes till you can release the brakes at the bottom.

  2. Gear down.

    As Eric pointed out, just because you won’t necessarily have brake fade, you will still nonetheless be prematurely wearing out your brakes. Also, if it is a windy road and you have to take some evasive action (for example some wildlife jumps out from the bush), I’d much rather be in a gear. If you’re concerned about all the high reving engine, just gear down to a ‘higher’ gear (i.e. you don’t have to ride down the hill in 1st or 2nd). The engine speed should ultimately be matching your driving speed — just as it would on a flat surface.

    The only case I could see for ‘coasting’ is if you certain you are actually NOT going to use the brake. For example, you’ve got a straight and clear line of sight on a large decline, and perhaps even see an incline is coming up in the distance. Sure, throw yourself in neutral enjoy the gravity ride, and ultimately the incline up in the distance will slow you down at some point (or more likely you’ll throw yourself back into gear to finish getting up the hill).

    Ultimately though riding the brakes is just as bad as riding the clutch. You’re going to prematurely wear out the system.

  3. As long as the engine is running then it is using some gas. Assuming throttle at “idle” then it isn’t going to use any more gas in any gear holding back the vehicle on a hill than idling in neutral while you wear out the brakes (well at least with fuel injection – a carb might suck more gas out of the jets because forced higher rpm means more air sucked through the carb).

    I just don’t see the wisdom of using brakes any more than you absolutely have to.

    Our car has over 100K miles. I’ve replaced the front disc pads twice and the rear drum shoes are original. I’ve got a box of new shoes sitting in the garage but why replace them when they are still about 50% of new?

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