A modern car does not use fuel when the foot is off the accelerator. This is by design.
If the downward slope of the road is sufficient to defeat the frictional forces of the engine (and tyres, transmission etc) and thus propel the car forward, the car will descend down the sloping road without using fuel at all.
If you take the car out of gear, the engine must use fuel to maintain the engine's idle speed. In-gear, gravity is doing the work for the engine.
Of course, if you are on a level, or uphill road, and take your foot off the accelerator, the car will still use no fuel but will gradually slow down due to the frictional forces of the wheels, transmission and engine.
I suppose that the optimal way to save fuel would be to put the car in neutral and cut power to the engine while going downhill -- since you would then be losing the engine's friction and not be needing to keep the engine going -- but with current cars this would lead to a loss of control. It wouldn't surprise me though if future cars brought in some method of doing this, however, and of course an electric motor would be capable of storing the energy whilst being pulled down a hill by gravity.
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The engine will use fuel in such circumstances, albeit a small amount. If your car can display instant fuel consumption go and give it a go. Or just try switching off the ignition and notice the difference.
Anyway coasting is dangerous, it reduces the driver's control over the car and should be discouraged at all times. I'm shocked HJ didn't point this out to his correspondent.
Edited by OG on 28/08/2010 at 14:20
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If your car can display instant fuel consumption go and give it a go.
Doesn't work. The system will display 99.9mpg whether in-gear or not, such is the small amount of fuel used in either case.
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OK, the display in your car has less resolution than others. Some will read to 999.9.
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If you travel down a slope, say doing 50 at the start, & by taking your foot off the throttle the car maintains 50 it is using no fuel. The vehicle is still using energy keeping the engine turning over at say 1500 RPM.
When you get to the bottom of the slope you have to immediately apply throttle or speed will be lost.
Travelling down the same slope, starting at 50, if you coast in neutral the vehicle will be using a small amount of fuel.
By the time you reach the bottom of the same slope the vehicle will have increased speed as it no longer has to drive the engine & will be now doing say 60.
The car will travel quite a distance until the speed has reduced back to 50, although will still use a small amount of fuel with the engine ticking over.
It will use less fuel than in the first instance by the time its speed has reduced back to 50.
Especially so with diesel engined vehicles as they use less fuel ticking over.
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"It will use less fuel than in the first instance by the time its speed has reduced back to 50."
Is this just a theory of yours, or do you have hard evidence?
I suspect that you might be right, but I don't know. My understanding is that
- one uses effectively no fuel while coasting in gear,
- one does use fuel when coasting in neutral, but considerably than when cruising normally,
- the amount of fuel used when coasting in neutral does not depend on the speed at which one is driving i.e. whether you are going at 20 mph or 70 mph you are using the same amount of fuel per second. The result that coasting in neutral can be reasonably fuel efficient when one is doing high speeds, but is not fuel efficient at lows speeds.
Hence when I am trying to save fuel, I do sometimes coast downhill.
I take the point about having less control of a car when coasting in neutral, but I think that the dangers of doing so are somewhat exaggerated - and that there are times when it is pretty safe, e.g. empty roads with good visibility.
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Hence when I am trying to save fuel, I do sometimes coast downhill.
I take the point about having less control of a car when coasting in neutral, but I think that the dangers of doing so are somewhat exaggerated - and that there are times when it is pretty safe, e.g. empty roads with good visibility.
I was taught by the IAM that it is fine to press in the clutch and roll to a stop, for example when approaching a queue of stationary cars. You still have control because it only takes a movement of one leg and foot to lift the clutch pedal. Coasting in neutral is not good because in order to get control, you have to use the gear stick, a much more complex operation, especially if a hazard appears.
I had never thought about rolling along with the clutch down versus normal driving, but it does make sense. It assumes that the engine uses no fuel when the accelerator pedal is not depressed, and not being an 'expert', I can only accept that as a fact.
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If your car can display instant fuel consumption go and give it a go.
Doesn't work. The system will display 99.9mpg whether in-gear or not, such is the small amount of fuel used in either case.
Here in metric land, you don't get divide by zero errors.
My wife's car uses 0.3 litres per hour coasting out of gear, and 0.0 litres per 100km in gear. So travelling downhill on the mountain road near to us in gear five times a week would save enough petrol to buy a cup of coffee out each week.
The alternative would be to stick the car in neutral, spend the coffee money on fuel, AND replace the brakes twice as often!
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It all depends weather you can use the energy gained by coasting to continue your journey
without having to brake.
In WKS's case, he has to keep braking down the mountain road so cant use the stored energy, so yes , more efficient to use engine braking & no fuel.
If it was just a straight road downhill then up the other side or on the level, you can use the stored energy to continue your journey & save fuel.
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Under certain conditions coasting can be the more economical option.
When coasting the engine uses a small amount of fuel to keep the engine running.
When on the overrun, in most instances modern engines use no fuel, however - engine friction and pumping losses and ancillaries running at a much higher rpm will mean more total energy lost than coasting as the vehicle is effectively being braked by the engine/ancillaries. You may then need to use more fuel to make up the lost energy later.
Its a complex problem - depends on many factors, engine friction/pumping losses and depends on what you are doing or trying to acheive e.g. coasting down a long shallow slope, approaching a junction etc. Sometimes one method is more economical, sometimes worse. And dont forget you may end up using your brakes harder and then the economy arguement gets even more complex.
You should only coast when safe to do so - which is not very often.
Edited by brum on 28/08/2010 at 18:10
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Coasting out of gear uses fuel idling engine.Coasting in high gear uses less fuel feet of the gas virtually nil.Coasting can be safe at certain times you have brakes on your car.Hybrid cars toyota under 30 miles the electric motor takes over no fuel used.
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With most diesel engines the injectors deliver no fuel to the cylinders when the engine is on over-run - as when going down hill in gear with foot off accelerator. But when the engine is on tickover they have to supply some fuel or the engine would stop.
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Whether or not fuel is delivered on the over-run, coasting obviously saves energy because it takes more energy to keep an engine rotating at 2,500 rpm than 700.
Special condition mentioned by brum e.g. A21 down by Sevenoaks, if you slip into neutral at the top at about 70mph and slip back into gear at the bottom at about 70mph, you will obviously use less fuel than if the car is kept in gear at the same speed between the same two points because it takes more energy to keep the engine and its ancillaries spinning at much higher revs.
As for 'coasting is dangerous' - that might have been true for a Model T Ford or a bullnose Morris, but not in modern cars!
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Tried this over the years since having mpg computers. Traffic is getting heavier and slower so on my homeward descent I tend to leave it in 6th gear to avoid catching up the the mobile queue. No measurable difference on odd occasion when I 've tried coasting against foot off in 6th gear. I got a freakish 62 mpg on the way home the latter way. Jury is still out.
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As for 'coasting is dangerous' - that might have been true for a Model T Ford or a bullnose Morris, but not in modern cars!
I can't see how you work that out, as the AA website says if you're coasting in neutral you can't accelerate out of a dangerous situation for one thing.
www.theaa.com/motoring_advice/fuels-and-environmen...l
Edited by OG on 29/08/2010 at 16:23
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Whether or not fuel is delivered on the over-run, coasting obviously saves energy because it takes more energy to keep an engine rotating at 2,500 rpm than 700.
Special condition mentioned by brum e.g. A21 down by Sevenoaks, if you slip into neutral at the top at about 70mph and slip back into gear at the bottom at about 70mph, you will obviously use less fuel than if the car is kept in gear at the same speed between the same two points because it takes more energy to keep the engine and its ancillaries spinning at much higher revs.
I think you and several others have missed the point being made. If you go down hill in gear without accelerating, then gravity is doing the work for you, keeping the energy turning over. According to one or more people, if you do not press the accelerator pedal, fuel is not injected into the pistons. But, go into neutral, and then fuel has to be burnt to keep the engine ticking over.
As for 'coasting is dangerous' - that might have been true for a Model T Ford or a bullnose Morris, but not in modern cars!
As I and others have indicated, when you coast, you are in neutral. If you come across a hazard, you are not in control of the car until you change into gear, and that takes time, slowing down your response. And if you are taken by surprise, you might be so shocked that you fluff the gear change. If you are already in gear, you can power your way out of danger, with no danger of fluffing a gear change. If you are in gear, but the clutch pedal is depressed, you can regain control in a fraction of a second.
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<<I think you and several others have missed the point being made. If you go down hill in gear without accelerating, then gravity is doing the work for you, keeping the energy turning over.>>
This does not make sense, Leif. I think what you are trying to describe is the effect of the potential energy released during the reduction in height, which without gravity would indeed be nil. The gravitational effect will be the same whether in or out of gear.
Having had a conversation with my more recently qualified son I now realise that a descent on the A21 is indeed powered by potential energy if the speed at start and finish is the same, whereas coasting along the flat A14 to the A1 roundabout from 70mph to 20 mph is powered by kinetic energy. However, this is an academic distinction which in no way detracts from my argument above .....that coasting obviously saves fuel because the engine spins more slowly. In the case of 'flat' coasting, if left in gear the frictional losses of the rapidly spinning engine, water pump etc would mean that you got to 20mph long before the roundabout, and so would have to press on the accelerator to reach it. A knowledge of theoretical physics would enable you to realise that this would inevitably use more fuel than the tiny amount being used to keep the engine idling.
It does take a certain skill to time the disengagement of gear and luck with an empty roundabout/green lights to enable its transition without braking - thus burning even more energy!
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No intention of joining the mpg debate but it seems to me that the issue of safety when coasting in neutral overlooks a key aspect of modern cars. Most family cars driven in top (5th or 6th) gear have almost no chance of suddenly accelerating out of danger without changing down. So its hard to see why having to change out of neutral would make much difference, might even be quicker. For the record, I never gave much thought to coasting more than a few yards until I saw this thread.
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This does not make sense, Leif. I think what you are trying to describe is the effect of the potential energy released during the reduction in height, which without gravity would indeed be nil. The gravitational effect will be the same whether in or out of gear.
No.
If the engine is running, and you are out of gear, the engine's natural equilibrium state is still -- i.e. no revs. In other words, stalled. The engine management system stops this from happening, and maintains the engine in an idling state. In other words, you're using the same amount of fuel as if the car were stood still and in neutral.
If the engine is running, and you are in gear, the engine wants to stop, but is unable to because of the gravity-induced motion of the driven wheels. No fuel is spent because gravity is being turned into engine motion by the transmission.
In other words, if you are out of gear, you are quite right to say that the engine does not need to use fuel, but if it did not, it would stall, as the gravitatonal effect is being disconnected by virtue of the clutch being disengaged. So fuel is spent preventing the stall.
To test the hypothesis, drain all fuel out of your car, and take it to the top of a fairly steep bank. The only way you will get that engine to turn is *in* gear, correct?
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This does not make sense, Leif. I think what you are trying to describe is the effect of the potential energy released during the reduction in height, which without gravity would indeed be nil. The gravitational effect will be the same whether in or out of gear.
It does make sense. When you are in gear, gravity pulls the car downhill, and turns over the engine. As you do not need to accelerate, no fuel is used. When you are not in gear, the engine would naturally slow down and stall, so the engine management unit keeps it idling which requires fuel to be burnt.
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Quite so, Leif. But at the bottom of the hill the car is much faster if coasting than if in gear. That extra kinetic energy must be more than the energy used to keep the engine ticking over because no energy has been expended on making it rev more rapidly than tickover.
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John - we're not saying it isn't using energy while descending a hill in gear, foot off accelerator. We're just saying it isn't using any fuel.
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Quite so, Leif. But at the bottom of the hill the car is much faster if coasting than if in gear. That extra kinetic energy must be more than the energy used to keep the engine ticking over because no energy has been expended on making it rev more rapidly than tickover.
Yes, that might be true, so that you could coast along the level at the bottom of the slope, except that coasting down a hill without braking is usually dangerous, as you get up too much speed. So you brake, and go down at the usual speed. I do prefer it when passengers are not screaming. Just one of my little quirks. :)
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If in-gear makes you slow down too much, move up a gear ;)
You'd have to be going at quite a pace for engine braking to be significant to the point of keeping you going too slow in fifth gear!!
Let me ask you a question; if you are going downhill on a motorway at 85mph, do you pull out of gear then as well?
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Let me ask you a question; if you are going downhill on a motorway at 85mph, do you pull out of gear then as well?
Seems to be an irrelevant question.
If you were trying to save fuel coasting, you wouldn't be travelling at 85 in the first place.
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Not an irrelevant question at all.
Coasting at such speeds comes under the "b***** lethal" category. Just an extreme example of what John F seems to be advocating.
If you are in a position where *accelerating* whilst coasting is going to save fuel, which is the example John F is referring to, this amounts to the same thing. b***** lethal, and I wouldn't want to be in the same car.
You either hold speed using engine braking (recommended), accelerate down the hill (lethal) or brake down the hill (not recommended -- false economy and unsafe in any case, even assuming that you are using more fuel).
I cannot think of a single case where accelerating down a hill is advisable -- indeed down most banks you're accelerating quite a lot even when in a lowish gear -- allowing your car to be controlled by the brake pedal in this case is a *bad idea* for a number of reasons:
1) You're effectively reducing your braking power by pushing the friction surfaces closer to their limit.
2) You run the risk of brake fade as the brakes heat up.
3) You are denying the person behind one way of telling if you're about to stop suddenly.
When you add on the fact that you're actually using more fuel by coasting/braking than using the engine, I see this as a non-question really.
And to re-iterate, free-wheeling down a bank is very, very stupid.
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If in-gear makes you slow down too much, move up a gear ;)
You'd have to be going at quite a pace for engine braking to be significant to the point of keeping you going too slow in fifth gear!!
Let me ask you a question; if you are going downhill on a motorway at 85mph, do you pull out of gear then as well?
Why are you trying to find an obscure case where coasting might save fuel rather than acknowledging that 99% of the time coasting down hill does not save fuel?
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Why are you trying to find an obscure case where coasting might save fuel rather than acknowledging that 99% of the time coasting down hill does not save fuel?
I'm not 'trying to find an obsure case' - I am merely mentioning a point of view. And I don't acknowledge that 99% of the time coasting doesn't save fuel because, with my accredited knowledge of physics and mechanics, I think it does and have done my best in this thread to prove it. So far, no-one with similar or superior credentials has disproved my argument, but if they do so I will happily change my mind. QED.
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I refer you to your original post. When I go down a shallow hill I do not need to accelerate. So the fuel used is zero. If I coast, fuel is used. That is the key. Your original post is confused because you say "It must surely need less energy to keep it rotating at 700rpm than at twice that speed - or more." Yes, that is true. But most if not all the energy required to keep it rotating at twice that speed or more is supplied by gravity. You yourself acknowledge that. Oh and some energy is collected by the battery on the way down.So it seems to me that your argument lacks a basic understanding. Sorry, but that is how it reads to me.
Edited by Leif on 01/09/2010 at 14:28
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<< . But most if not all the energy required to keep it rotating at twice that speed or more is supplied by gravity. You yourself acknowledge that. Oh and some energy is collected by the battery on the way down.So it seems to me that your argument lacks a basic understanding. >>
Leif, I think it is your argument lacks basic understanding. I don't acknowledge that at all. Gravity is a force, not a free supply of energy. It is something that gives weight to mass. It cannot power anything. For a car to gain the energy expended in frictional losses while coasting down a hill it must first burn fuel to overcome gravity to get to the top of the hill. It is that fuel that has provided that energy, not 'gravity'.
The only way to save fuel using gravity is to buy your car from a dealer at the top of the hill and sell it to one at the bottom!
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Leif, I think it is your argument lacks basic understanding. I don't acknowledge that at all. Gravity is a force, not a free supply of energy. It is something that gives weight to mass. It cannot power anything. For a car to gain the energy expended in frictional losses while coasting down a hill it must first burn fuel to overcome gravity to get to the top of the hill. It is that fuel that has provided that energy, not 'gravity'.
The only way to save fuel using gravity is to buy your car from a dealer at the top of the hill and sell it to one at the bottom!
You are taking a theoretical viewpoint which does not correspond to the real world except in very unusual circumstances. And you ignore safety.
We do not live in a perfect world with no traffic and perfectly straight roads that go up and down. In the real world, you don't freewheel to the bottom of the hill and part way up the next hill, mainly because that would be astoundingly dangerous. Instead you brake to keep your speed down to a safe level, which will convert some of the kinetic energy of the car into heat and sound. And the chances are you will come to a corner, in which case you will brake further, thereby getting rid of even more of the kinetic energy of the car gained by freewheeling down the hill.Or you will meet traffic, forcing you to slow down.
What do you do when you see stationary traffic ahead? Do you depress the clutch, and coast, or do you just remain in gear? The fuel efficient approach is to stay in gear, and brake gradually.
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Let me ask you a question; if you are going downhill on a motorway at 85mph, do you pull out of gear then as well?
I would not dream of incriminating myself by a direct answer to your question, only to say that I try to make rapid but efficient progress. This includes nudging the auto into N at any speed, no matter how great.
Any force that slows a car requires burnt fuel to overcome it. We can't do much about wind resistance [unlike the swallows returning to Africa I do not yet plan motorway journeys to coincide with a following wind] or about frictional losses apart from keeping tyres well inflated. But braking, whether by engine/ancillary mechanical friction or by drum/disc mechanical friction, is under the driver's control and to save fuel [and brake wear] it is best to do it as little as possible. [I change pads rarely and the front discs on our old family Passat lasted till 200,000 miles with careful derusting maintenance every so often - admittedly these were mostly dual-carriageway miles with little braking.]
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I'll pitch in here and and maybe help clear this one up a bit.
John F is correct, but maybe not explaining it very clearly.
Lets firstly state a couple of facts:
1 - A modern car will use no fuel when on the overrun, i.e in gear going down hill
2 - A car in neutral with the engine ticking over will be useing some fuel
3 - MPG is calculated by distance travelled divided by fuel used
Some of you are focused on points 1 and 2 - but forgetting point 3
A car in neutral will travel further than a car in gear, so despite the fact that it uses some fuel to keep the engine ticking over, it travels much further.
Coasting in neutral works when you can allow the car to gather momentum down the hill and make use of that momentum to continue on the next flat or uphill section.
If you have to come to a stop at the bottom of the hill then you are better off leaving it in gear.
Hope that makes sense.
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I think i get a donkey :)
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I think i get a donkey :)
I saw a nice used donkey in the classifieds section, one careful owner, FSH, low mileage, own teeth. Attach a couple of pairs of roller skates and you'll be able to coast down hill.
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I like the own teeth Leif.:)
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A car in neutral will travel further than a car in gear, so despite the fact that it uses some fuel to keep the engine ticking over, it travels much further.
I don't get that
If a car is in neutral surely it will coast/freewheel until it reaches an obstruction (ie an incline) which will interrupt its momentum and cause it to come to a halt.
If it is in gear it will continue to move forwards under the power of its engine whatever the road conditions
Edited by Armstrong Sid on 02/09/2010 at 09:42
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But even if there is a hill the car in neutral will go further than the one in gear (assuming the accelerator is not touched). My car would probably stall in 6th gear at 25mph feet off.
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But even if there is a hill the car in neutral will go further than the one in gear (assuming the accelerator is not touched). My car would probably stall in 6th gear at 25mph feet off.
The car in neutral uses fuel, the car in gear doesn't. So each car reaches the bottom of the hill, at the speed limit say, then each carries on. Let's assume no traffic ahead, no stopped cars, no bends. The 'normal' car drives along using fuel. The coasting car coasts along, slowing down, people behind hooting because the driver is intent on saving fuel. Mmmm. Is that how you drive? Of course not.
Anyway, coasting is generally recognised to be dangerous.
What relevance does your last comment have?
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Never heard of engine braking?
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Never heard of engine braking?
What point is your condescending remark intended to make? Please say your point rather than being condescending .
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Never heard of engine braking?
What point is your condescending remark intended to make? Please say your point rather than being condescending .
That post was in response to this:
I don't get that
If a car is in neutral surely it will coast/freewheel until it reaches an obstruction (ie an incline) which will interrupt its momentum and cause it to come to a halt.
If it is in gear it will continue to move forwards under the power of its engine whatever the road conditions
A coasting car will stop much sooner if it is in gear due to energy being used to turn the engine - engine braking as its most commonly called.
So Leif, who rattled your cage today? And anyway the thread is about which is the most fuel efficient way to coast - not about wether its safe or not, so plase stay on topic, there's a good chap.
:)
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Keep it polite and constructive please chaps.
I'm interested that no-one has challenged my very basic, simplistiv point that I'll repeat:
"We're not saying it isn't using energy while descending a hill in gear, foot off accelerator. We're just saying it isn't using any fuel."
Andy - I can't resist pointing out that a wether (your last line) is a castrated sheep. Highly appropriate as it doesn't run on full power.....
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' And anyway the thread is about which is the most fuel efficient way to coast '
Nice to see someone is paying attention. ;}
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Never heard of engine braking?
What point is your condescending remark intended to make? Please say your point rather than being condescending .
That post was in response to this:
I don't get that
If a car is in neutral surely it will coast/freewheel until it reaches an obstruction (ie an incline) which will interrupt its momentum and cause it to come to a halt.
If it is in gear it will continue to move forwards under the power of its engine whatever the road conditions
A coasting car will stop much sooner if it is in gear due to energy being used to turn the engine - engine braking as its most commonly called.
So Leif, who rattled your cage today? And anyway the thread is about which is the most fuel efficient way to coast - not about wether its safe or not, so plase stay on topic, there's a good chap.
:)
I am on topic dear boy, just not the same one as you. Since you did not quote, I did not know who you responded to.
You will have to define the question that you wish to answer, because it is far from clear. If we consider two cars going down a hill, ignoring safety concerns, and the real world, and record the speed at the bottom, clearly the car that is not in gear will be going faster, and hence will have more kinetic energy. Will that kinetic energy be more than the energy expended in idling the engine?
At the bottom of the hill the kinetic energy (KE) of the in gear car will be the potential energy at the top of the hill (PE), minus the energy lost due to engine braking (friction and heat) minus the energy lost due to air resistance. And the KE of the not in gear car will be the PE minus the energy lost due to wind resistance. There are a few other factors, such as rolling friction, and so on.I think you would have to experiment to determine how significant wind resistance is, and how it varies with speed, and how engine braking compares to burning fuel.
I don't think the above has got us anywhere. :) Except that I will rabbit on again about how this does not tell us much about the real world.
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Interesting debate so if a car is out of gear(freewheeling)it uses more fuel than coasting in gear no engine braking and out of gear the car travels further exept when approaching a hill out of gear.But if in gear approaching the hill the engine cuts out if there is no feet on the accellerator .Its all starting to sound double dutch to me we have to do a test with a few cars auto's included.:)
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Its all starting to sound double dutch to me we have to do a test with a few cars auto's included.:)
It's been an enjoyable debate [thanks to all partakers] but it's basically very simple. It takes more energy to make an engine spin quickly than spin slowly. The only energy source is fuel.
Transient changes in kinetic and potential energy are irrelevant as both forms are originally supplied by the fuel. Whether or not fuel is injected when foot is removed from accelerator is also irrelevant. If it isn't, more kinetic/potential energy has to be used up to keep it going.
So coasting must save fuel.
QED.
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So coasting must save fuel.
QED.
Only in an idealised world with no traffic, hazards, speed limits or people behind parping you when you coast along at 20 mph in a 50 mph limit. In the real world coasting rarely saves fuel for the reasons explained earlier.
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So its a bit like us mere mortals.When we run we use more fuel (not me) than walking.When we sleep (coasting) we use very little fuel so sleeping must save fuel.:)
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A coasting car will stop much sooner if it is in gear due to energy being used to turn the engine - engine braking as its most commonly called.
I'm not so sure you are right. I did a few casual tests today, comparing the car with no acceleration and in gear, and out of gear, on a flattish stretch of road. I was surprised that there was no significant and obvious difference in the rate of slowing down, which suggests that the dominant force on the car is wind resistance, not engine braking. This was at about 40mph. I must admit that I was surprised. The car was in a high gear, to ensure as few 'pointless' cylinder compressions as possible since I assume that is the main source of the braking. Clearly there must be engine braking, but it is not as obvious as I expected.
What many of us perhaps think of when engine braking is mentioned is the sudden slowing down when the car is dropped a gear, and the engine is not turning over fast enough to match the new gear. I used to do that when learning to drive, and the instructor did not mind, which is a bit daft as it wears the engine, and it is advised against, brakes being cheaper to replace.
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This is getting rather silly.
You're all going off on a tis,tisnot,tis not,tis,tis not rant.
Its boring, a lot of piffle presented improperly as fact.
There ought to be a law against it.
Get the backroom police in quick - or are they too busy patrolling the middle lane of the motorway or reporting fog light users???
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On thing about you Leif you wont give up, like a terrier with a bone.:)
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On thing about you Leif you wont give up, like a terrier with a bone.:)
Dunno. The OP has arrived at a conclusion with zero proof. Physics is based on experiment, and without that, there is nothing.
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On thing about you Leif you wont give up, like a terrier with a bone.:)
Dunno. The OP has arrived at a conclusion with zero proof. Physics is based on experiment, and without that, there is nothing.
My conclusion is indeed based upon theory rather than experiment - but the laws of physics involved here have long since been proven and require no further experiment. The question is, have I converted the authority figure whose dogma has been so tenaciously upheld by Leif et al - or am I to be excommunicated?
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My conclusion is indeed based upon theory rather than experiment - but the laws of physics involved here have long since been proven and require no further experiment. The question is, have I converted the authority figure whose dogma has been so tenaciously upheld by Leif et al - or am I to be excommunicated?
Your conclusion is based on numerous untested assumptions combined with some physics. An argument is only as strong as the weakest link. Actually to me it seems that you are being dogmatic, as you are drawing conclusions based on your beliefs. I have no idea how much fuel is consumed by idling, and how much 'equivalent fuel' (for want of a better term) is consumed by engine braking. I've not seen how engine braking compares with braking from air resistance. And I've seen no figures from anyone, so quite how we can draw firm conclusions is beyond me.
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<<<Your conclusion is based on numerous untested assumptions combined with some physics. An argument is only as strong as the weakest link. Actually to me it seems that you are being dogmatic, as you are drawing conclusions based on your beliefs.>>>
It's not belief, Leif, it's knowledge. Some assumptions were tested over 2000 years ago by the Greeks. Proven theory that will translate to predictable experimental result. You either understand physics and mechanics or you don't. What are your independently examined qualifications that might support your capability of understanding the theoretical argument? You are confusing dogma with authority, methinks.
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This is getting rather silly.
You're all going off on a tis,tisnot,tis not,tis,tis not rant.
Oh no we're not ...
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We have to talk to professor Hieneken from Amsteldammer and professor Grolch from Slaphenhousen who works for bavarian motorwerke to get to the bottum of this!!
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You do that, and when you have explored the bottum, let is know what you have found.
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Lets forget about going downhill traffic feet on on gas or if its safe to coast or not.Or wind factors.A straight road iam driving at 60mph.Iam in 5th gear and take my feet of the accellerator how far will i travel before the engine cuts out?Say at 60mph i take the car out of gear and put the gearstick in neutral engine is ticking over will i cover more distance no engine braking.So which is more eonomical and when is more fuel used.?Me thinking the engine uses less fuel when coasting in gear but covers less distance engine braking.I have to try it out next week ,not tomorrow sunday is a day of rest.
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It is far from trivial. Considering simple coasting as you suggest, is engine braking consuming more energy (kinetic, from the car's motion) than engine idling is consuming (fuel, which could have been converted into kinetic energy)?
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Good afternoon Leif,kinetic energy as i understand it is the power needed to accelerate a body of a giving mass from standstill.And the object maintains this energy unless its speed changes.(kinetic energy) When a car is coasting you will lose kinetic energy speed is not maintained slowing down.
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I don't understand what point you are making. What I wrote is correct.
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With respect, you are both talking twaddle.
Please desist or you I will be forced to give you both three points.
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Has anyone anything fresh to say on this subject? I'm reluctant to stifle free speech by locking the thread, but it may be an idea to agree to disagree before anyone gets too abusive.
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Excellent Brum you are the expert
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You have a fixed-wheel bicycle, and are at the top of a long steep hill.
Do you:
a) keep your feet on the pedals as you descend slowly, and then have to pedal up the next hill,
or
b) Lift your feet off the pedals and race down the hill and get halfway up the next one before you have to pedal again?
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You have a fixed-wheel bicycle, and are at the top of a long steep hill. Do you:
a) keep your feet on the pedals as you descend slowly, and then have to pedal up the next hill,or
b) Lift your feet off the pedals and race down the hill and get halfway up the next one before you have to pedal again?
Thats quite a good analogy, Cliff!
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Has anyone anything fresh to say on this subject? I'm reluctant to stifle free speech by locking the thread, but it may be an idea to agree to disagree before anyone gets too abusive.
Please keep this going just long enough to see how narrow the blue quote boxes can get
Edited by Armstrong Sid on 07/09/2010 at 07:58
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Going downhill pedal fast ,when arriving at bottum of hill,lift feet off pedal carefull not to trap ones feet when bikes slows down up hill start pedalling again like the clappers.:)
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Nuffin
A world champion boxer takes his bicycle to the movies.Because bikes are often stolen,he hangs a sign on his bike.Don't steal or else!! After the film his bike was stolen.A sign lays on the floor. Following me won't work.( World Champion Cyclist.:)
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If you stare at the blue lines for long enough.....
The discussion could be considered a little futile anyway, do people really care about those few extra mpg?
Lets put this thread to rest and re visit once petrol hits £2 a litre.
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The discussion could be considered a little futile anyway, do people really care about those few extra mpg?
I think that good driving practices are worth having, which includes seeing ahead, keeping a safe distance, not braking often, using a high gear when feasible and can give substantial fuel savings, as well as less wear on the engine and other components.
Back to staring at the blue line.
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Are we still on this subject? Getting narrower.
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Are we still on this subject? Getting narrower.
Dunno.
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Nearly there.
Just another little push ...
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Nearly there.
Just another little push ...
I don't see what your sex life has to do with this discussion....
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Getting narrower ...
Just like a backroomer's mind.
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Getting narrower ...
If the blue lines meet, your computer will self-destruct
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