Coasting on hills?

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traintracks1995
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#1
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Should I coast down hills or simply just come off the gas pedal to save fuel?
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Extremotroph
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Fuel economy is dependent on the level of throttle you engage.
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the bear
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something might happen suddenly... a deer could leap out... you need to be in full control at all times
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Camoxide
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#4
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(Original post by traintracks1995)
Should I coast down hills or simply just come off the gas pedal to save fuel?
You use no fuel when you take your foot off the throttle. Might be slightly different in a diesel but in a petrol:
Say you take your foot off the gas at 50. You'll use no fuel from now on until you slow down to a point (30ish) where the engine starts injecting fuel again to stop it stalling. The engine is kept running by the wheels before that.

However on say A roads going down a hill: taking your foot off the gas slows the car down too much so you have to keep your foot on the gas to keep up the speed. This is where it'd be better (but more dangerous) to Coast as gravity will speed you up without any resistance from the engine.
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traintracks1995
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(Original post by Camoxide)
You use no fuel when you take your foot off the throttle. Might be slightly different in a diesel but in a petrol:
Say you take your foot off the gas at 50. You'll use no fuel from now on until you slow down to a point (30ish) where the engine starts injecting fuel again to stop it stalling. The engine is kept running by the wheels before that.

However on say A roads going down a hill: taking your foot off the gas slows the car down too much so you have to keep your foot on the gas to keep up the speed. This is where it'd be better (but more dangerous) to Coast as gravity will speed you up without any resistance from the engine.
I don't buy the argument that coasting is dangerous. Say I was in the slow lane on the motorway "coasting" at 60 mph. It's not dangerous, and even if something were to happen in front of me, I have the brakes.
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The Jargen
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(Original post by traintracks1995)
I don't buy the argument that coasting is dangerous. Say I was in the slow lane on the motorway "coasting" at 60 mph. It's not dangerous, and even if something were to happen in front of me, I have the brakes.
It takes longer to stop though because the engine is disconnected. When going down a hill put it in a higher gear and gently apply the gas.
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Camoxide
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(Original post by traintracks1995)
I don't buy the argument that coasting is dangerous. Say I was in the slow lane on the motorway "coasting" at 60 mph. It's not dangerous, and even if something were to happen in front of me, I have the brakes.
It's removes you're ability to accelerate away from a dangerous situation.

I coast when I can on A roads
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traintracks1995
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(Original post by The Jargen)
It takes longer to stop though because the engine is disconnected. When going down a hill put it in a higher gear and gently apply the gas.
My car has superb brakes and I leave enough gap in front of me anyway when I coast

(Original post by Camoxide)
It's removes you're ability to accelerate away from a dangerous situation.

I coast when I can on A roads
Meh, I don't consider either of these to be of any concern
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The Jargen
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(Original post by traintracks1995)
My car has superb brakes and I leave enough gap in front of me anyway when I coast



Meh, I don't consider either of these to be of any concern
It may very well, but the car continues to pick up speed. That's why it's better to keep the engine engaged.
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Alfissti
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(Original post by traintracks1995)
Should I coast down hills or simply just come off the gas pedal to save fuel?
Why bother? Can't afford that 7-series otherwise?
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fluttershy
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When you're coasting you're using fuel to keep the engine turning, wheras when you're off the throttle with the clutch and gears engaged the engine is being driven by the wheels and the fuel injection is turned off (same for petrol and diesel). You might have to use a little throttle to maintain speed on downhills, but the fuel used will be no more than what would be being used to keep the engine turning if coasting. Basically, it will use the same or more fuel, so it's daft regardless of it's supposed safety aspects.
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JC.
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In a modern fuel injected engine, the injectors will stop firing so no fuel will make it into the cylinders. By coasting you actually use more fuel as the injectors continue to work to keep the engine idling.
Similarly, you lose any assistance you get from engine braking - even in a car with good brakes and even in automatics this will make a difference to your stopping distance.
You lose the ability to accelerate at a moments notice.

Unless your engine has cut out and you're trying to maintain enough momentum as possible to get the car to the side of the road, there's absolutely no reason to coast ever.
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Nuffles
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#13
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What JC said. I've never been in a situation where I needed or wanted to coast ever (except when I hit 80 in the Morris Minor once).
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345rty
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#14
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I do, but I'm on carbs.
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College_Dropout
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I always coast
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blue n white army
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#16
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never felt the urge to coast, what's the point?
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traintracks1995
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#17
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(Original post by blue n white army)
never felt the urge to coast, what's the point?
Learn to read before posting. Save fuel
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blue n white army
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#18
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#18
(Original post by traintracks1995)
Learn to read before posting. Save fuel
Which you wont, did your driving instructor not cover this?
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IntriguedUser
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#19
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#19
More importantly, why do people slow down when goign down hill, just chuck it in neutral and let the hill do all the work, so annoying..

Do you know how far a car will roll from 40mph if you chuck it in neutral!! quite far
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knowledgenow
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#20
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Coasting is dangerous, and does not save fuel at all.

http://www.popularmechanics.com/cars...l-fuel-economy
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