Coasting advice
Discussion
I've always used neutral when coming to a halt to save some wear n tear, and to save a little fuel. With my Tax Disc reminder there's a 'how to save money' leaflet that states DONT use neutral when costing as this uses MORE fuel compared to staying in gear with no throttle. Is this correct?
Easy to spot if you have an mpg readout trip computer. If I come off the throttle the meter instantly max's out as no fuel is being put in to the engine. Coasting in neutral or with my foot on the clutch will obviously give a high reading but not off the gauge as it's still suing fuel to turn the engine over.
Watchman said:
Not illegal insofar as an identified offence but could be prosecuted as careless driving.
Indeed. Probably unlikely to ever be prosecuted for it, per se, but it would not go well if you collide with something and had lost engine braking and were unable to utilise power if it were needed to get out of trouble or to stabilise the car.That apart, exactly how many ml of fuel do you suppose this could ever save? You'd save more by paying 1p less a litre.
Watchman said:
doogz said:
LuS1fer said:
I believe so as deceleration cuts off the fuel. Coasting is also illegal as you are not infull control of your car.
Illegal? Really?matthias73 said:
No, it really couldn't. If you had the engine turned off, then yes..
Incorrect. Any non-compliance with the Highway Code can be used against you. the Highway Code says:Rule 122
Coasting. This term describes a vehicle travelling in neutral or with the clutch pressed down. It can reduce 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
There would still need to be a correlation between coasting and overall effect but the Highway Code is admissible in evidence.
LuS1fer said:
matthias73 said:
No, it really couldn't. If you had the engine turned off, then yes..
Incorrect. Any non-compliance with the Highway Code can be used against you. the Highway Code says:Rule 122
Coasting. This term describes a vehicle travelling in neutral or with the clutch pressed down. It can reduce 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
There would still need to be a correlation between coasting and overall effect but the Highway Code is admissible in evidence.
matthias73 said:
Well I of course admit it gives you less control, but coasting in itself can't be prosecuted for driving without due care and attention, unless he does something else, like hit a tree as a result of not being in gear.
Obviously - like you can't be prosecuted for speeding or using a mobile phone unless you get caught.LuS1fer said:
matthias73 said:
Well I of course admit it gives you less control, but coasting in itself can't be prosecuted for driving without due care and attention, unless he does something else, like hit a tree as a result of not being in gear.
Obviously - like you can't be prosecuted for speeding or using a mobile phone unless you get caught.the tricky answer is, it depends...
even on cars with fuel cut off, energy is lost as the engine is turning over at, say, 2000rpm. if you were coasting, the engine is only turning over at 700rpm, which uses less energy.
The sources for the energy is different - kinetic energy vs the energy stored in your fuel. However, this use of excess kinetic energy may be free to you, particularly if, for example, you were going to stop\slow at the end of your 'coasting' stretch any way.
if you were planning to carry on at the bottom of the hill at the speed at which you arrive there when coasting or faster, you are better (on fuel) to coast.
this massively simplifies things, such as eliminating the fact that the extra 2mph faster you're going will use more energy heating up air, and that an engine's efficiency is the same at 700rpm as at 2,000rpm. but a bunch of trucks now use the equivilent of a bycycle freehub (as did old 2 stroke saabs, but that was to get oil into the engine) so it can't be that bad. nearly every hybrid will shut down the petrol engine whilst you're off the throttle too
even on cars with fuel cut off, energy is lost as the engine is turning over at, say, 2000rpm. if you were coasting, the engine is only turning over at 700rpm, which uses less energy.
The sources for the energy is different - kinetic energy vs the energy stored in your fuel. However, this use of excess kinetic energy may be free to you, particularly if, for example, you were going to stop\slow at the end of your 'coasting' stretch any way.
if you were planning to carry on at the bottom of the hill at the speed at which you arrive there when coasting or faster, you are better (on fuel) to coast.
this massively simplifies things, such as eliminating the fact that the extra 2mph faster you're going will use more energy heating up air, and that an engine's efficiency is the same at 700rpm as at 2,000rpm. but a bunch of trucks now use the equivilent of a bycycle freehub (as did old 2 stroke saabs, but that was to get oil into the engine) so it can't be that bad. nearly every hybrid will shut down the petrol engine whilst you're off the throttle too
I don't understand these leaflets that they send out. I'm sure the one I received said to change gear before 2k RPM - if I was to do that in the civic it would cause the engine to labour, causing more fuel to be used and more wear/tear on the engine.
However, I do generally change gear at 2k RPM in the MPS to avoid using 'boost'.
However, I do generally change gear at 2k RPM in the MPS to avoid using 'boost'.
EdT said:
I've always used neutral when coming to a halt to save some wear n tear, and to save a little fuel. With my Tax Disc reminder there's a 'how to save money' leaflet that states DONT use neutral when costing as this uses MORE fuel compared to staying in gear with no throttle. Is this correct?
Correct.Just to put that in perspective, a modern diesel's pre-turbo exhaust temps can go as low as 60C if you coast for long-enough. They don't burn any fuel.
I am with the bunch who state that coasting (engine out of gear, idling on its own by using fuel) should use more fuel than simply running the same route in gear with no fuel going into the engine.
Unfortunately, Porsche have done this: http://www.youtube.com/watch?v=OGAmknR4D78 . I say unfortunate because it runs contrary to what I understand to be true.
Consequently I'm none the wiser as to which is more efficient.
C
Unfortunately, Porsche have done this: http://www.youtube.com/watch?v=OGAmknR4D78 . I say unfortunate because it runs contrary to what I understand to be true.
Consequently I'm none the wiser as to which is more efficient.
C
EdT said:
My car is a non-turbo diesel Lupo 1.7 - old school diesel. So, from reading your responses, coasting WONT save fuel correct?
Depends. If it's mechanically injected, then no. If it's electronically controlled as most are these days, then it will. I don't know offhand which the Lupo is. ETA: A brief spot of Google research suggests the car has an ECU, so it is likely to cut the fuel when the throttle is closed when in gear, so ought to be a bit of a saving compared to coasting out of gear.
Edited by Super Slo Mo on Tuesday 15th May 12:01
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