Why Coasting Is Bad
I believe Luis will be posting about engine braking sometime soon. It involves keeping the engine engaged (meaning engine is in gear, particularly for stick-shifts) even when not accelerating, or when slowing down. Let me do a quick post on coasting and its negative effects.
Some drivers I know coast along the road in neutral whenever they’re slowing down, or when going downhill. This is mostly done to conserve fuel. However, coasting may not necessarily be safe.
This term describes a vehicle travelling in neutral or with the clutch pressed down. Do not coast, whatever the driving conditions. It reduces driver control because
* engine braking is eliminated
* vehicle speed downhill will increase quickly
* increased use of the footbrake can reduce its effectiveness
* steering response will be affected particularly on bends and corners
* it may be more difficult to select the appropriate gear when needed.
Some would argue that it’s cheaper to wear out your brake pads rather than wear out a clutch due to engine braking. Still, the cost of getting into accidents (to property, life, and limb) is definitely greater than whatever marginal savings in fuel costs and brake pads you will get from coasting.
Here’s what I recommend. If you’re not familiar with engine braking, just be sure to keep your clutch engaged when slowing down, sticking to the current gear you’re in, and applying the brakes when you need to stop already or decrease speed. Don’t worry, your engine will still have enough torque up to a certain speed, and you won’t stall. When you reach the minimum speed your gear can take (usually around 15 to 20 Kph in 4th/5th gear, in my experience), you can then disengage the clutch and/or go into neutral. If you find the need to accelerate again, then you can downshift (usually into 2nd gear, depending on your speed).
Written by J. Angelo Racoma on April 17, 2007 | 10 Comments Leave a Comment
I could attest to this. You lose 80% of stopping power when you disengage gears. You also risk of popping them (brake lining) should you hit the brakes too hard for a sudden stop while running at high speeds. At that point no amount of engine breaking would help.
This is a good post to inform everyone about safety on the road. No matter how safe you are as a driver, if other drivers aren’t, you can never be totally safe.
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All good points about why coasting is bad. However, just to shatter a myth about coasting down hill ……
If you are coasting downhill, apart from loss of control and engine braking – you ARE using fuel, i.e. the amount the engine uses ‘ticking over’. If you are in a suitable gear for the steepness of the hill, not only do you maintain full control of the vehicle, you are using NO fuel.Some folk take things even further by turning the engine off going downhill. Very dangerous! You loose power steering and many cars these days have power assisted braking too. Then there is the possibility of the steering lock kicking in.
So, as the Highway Code says – coasting should be avoided at all times.
You don’t lose 80% of your stopping power when coasting. Whoever said that has never driven a car. Try it some time on an empty chunk of road (outside the UK to be strictly legal). An 80% reduction in stopping power would mean your stopping distance would become over twice as long. That certainly doesn’t happen.
If there is a difference, it’s fairly subtle.
Ah. I see. Some people take “coasting” to mean turning off the engine. That is indeed incredibly stupid. When the engine stops, your power steering and brakes stop being powered and your steering wheel may lock. Without power steering, you might indeed lose most of your braking power.
The more sensible definition of “coasting” is stepping on the clutch or shifting into neutral. That’s what I was talking about in my previous post.
What a load of crap.
As somebody said, coasting does not reduce your braking ability by 80%. That is just a ridiculous claim.
Also, turning of the engine will not cause your steering to lock. Steering locks only engage then the engine is off AND THE KEY HAS BEEN REMOVED FROM THE IGNITION. Grant, turning off the engine and removing the key whilst moving is idiotic, but turning off the engine isn’t.
And who said that you don’t use fuel if you’re in the appropriate gear? That man is also a fool. If your wheels are engaged with the clutch, and your wheels are moving, then your engine is at LEAST ticking over. And if the engine is doing any revs at all, it is using fuel. If we were to avoid ALL issues regarding safety and control, and talked solely about fuel economy, then turning off your engine and disengaging the clutch is the most fuel efficient way to go down a hill.
The difference in control when coasting and when not coasting is absolutely minute. In the original post, they talk about ‘going round corners being dangerous’. This is true, but as for going down hill, or straight, or anything before a turn, coasting is fine. As long as you are in gear before you start your turn, then there is nothing to fear.
Losing power steering and brake power may be an issue. But in the car I drive there is no power steering or power assisted braking anyway. So I can do whatever the fuck I want.
“And who said that you don’t use fuel if you’re in the appropriate gear? That man is also a fool. If your wheels are engaged with the clutch, and your wheels are moving, then your engine is at LEAST ticking over. And if the engine is doing any revs at all, it is using fuel. If we were to avoid ALL issues regarding safety and control, and talked solely about fuel economy, then turning off your engine and disengaging the clutch is the most fuel efficient way to go down a hill.”
Personally checked this on a computer connected to the ECU. When coasting ECU is injecting fuel, when at revs higher than tickover no fuel is injected if the accelorator is not depressed. You are thinking of simple carbourettor systems which havn’t been used in most cars for over 2 decades. Infact all new cars since around 2000 will have computer controlled fuel injection due to legal reasons.
Hmm if your coasting the engine is ticking over and using fuel, ok that’s fine, but how far will the car roll i wonder because it sure as hell wont be as far as the same practise with the clutch disengaged, that’s why its called engine braking. The pulse n glide technique used by hypermilers to get high mpg uses coasting to conserve fuel. Drive at 70 coast down to 50 and repeat
good article, I love scanning it. I hope 1 day I will acquire the same. cheers.