Coasting

Bluefox21

Recently I have been cheaping it up a bit by putting my foot on the clutch when going down hills or anything to save petrol. I remember my driving instructor (quite a while back now) & my folks telling me not to do this but can't remember why. Anyone know why?

And on a separate note was doing just under 130km/h on an empty & dry motorway (irrelevant I know) saw a speed camera ahead slowed to about 124 as I was going past.... Didn't see a flash does that mean I am ok last thing I need now is an 80 euro fine .

colm_mcm

lots of people will point out that on modern engines, they use no fuel while coasting, however the engine does have a braking effect

corktina

coasting is not a good idea as it lessens your control of the car and depressing the clutch causes wear so negates the saving in petrol....

your speedo like most is probably about 10% inaccuate so you would be safe at 124 imho

AugustusMinimus

Bluefox21 wrote: »

And on a separate note was doing just under 130km/h on an empty & dry motorway (irrelevant I know) saw a speed camera ahead slowed to about 124 as I was going past.... Didn't see a flash does that mean I am ok last thing I need now is an 80 euro fine .

No irrelevant at all. New motorways in Ireland have a design speed of 160kph.

Nissan doctor

Bluefox21 wrote: »

Recently I have been cheaping it up a bit by putting my foot on the clutch when going down hills or anything to save petrol. I remember my driving instructor (quite a while back now) & my folks telling me not to do this but can't remember why. Anyone know why?

And on a separate note was doing just under 130km/h on an empty & dry motorway (irrelevant I know) saw a speed camera ahead slowed to about 124 as I was going past.... Didn't see a flash does that mean I am ok last thing I need now is an 80 euro fine .

Coasting out of gear uses fuel as the engine is idling, Coasting in gear(just off the accelerator) uses no fuel as the forward motion, through then transmission, is keeping the engine running.


As for the speed camera, the chances that there was even a camera in the box is slim, but I doubt it would go off at 124. Also 124 on the speedo will actually be under 120kmh.

Andrew33

Coasting is also known as an Aberdeen overdrive or Scottish topgear, and I've heard of people knocking autobox's into N and destroying the 'box in pretty short order.

colm_mcm

Nissan doctor wrote: »

Coasting out of gear uses fuel as the engine is idling, Coasting in gear(just off the accelerator) uses no fuel as the forward motion, through then transmission, is keeping the engine running.

I suppose unless you could calculate how much farther you could coast in neutral using the tiny amount of fuel needed to keep the engine idling it's hard to know if it's more or less efficent.

Bluefox21

Nissan doctor wrote: »

Coasting out of gear uses fuel as the engine is idling, Coasting in gear(just off the accelerator) uses no fuel as the forward motion, through then transmission, is keeping the engine running.


As for the speed camera, the chances that there was even a camera in the box is slim, but I doubt it would go off at 124. Also 124 on the speedo will actually be under 120kmh.

It was a Garda car & camera be sickened if I get done for it so easy to drift above 120 when you've the road to yourself. Hope they let you off with that 10%. Rev count still high even when not using accelerator drops to 1 when idling or "coasting". Car just rolls down the hill slows down but only gradually then back into gear at bottom of hill

Wishbone Ash

Bluefox21 wrote: »

It was a Garda car & camera be sickened if I get done for it so easy to drift above 120 when you've the road to yourself. Hope they let you off with that 10%. Rev count still high even when not using accelerator drops to 1 when idling or "coasting". Car just rolls down the hill slows down but only gradually then back into gear at bottom of hill

Coasting does not save any fuel - travelling more slowly on the motorway will.

pajo1981

Bluefox21 wrote: »

Recently I have been cheaping it up a bit by putting my foot on the clutch when going down hills or anything to save petrol.

Cheapening it up? You use more fuel putting your foot on the clutch.

If you want to save fuel don't go near the clutch when coasting to a stop.

Nissan doctor

Bluefox21 wrote: »

It was a Garda car & camera be sickened if I get done for it so easy to drift above 120 when you've the road to yourself. Hope they let you off with that 10%. Rev count still high even when not using accelerator drops to 1 when idling or "coasting". Car just rolls down the hill slows down but only gradually then back into gear at bottom of hill

Yes but as I said, at idle the engine is injecting fuel to stay running, when coasting in gear, the transmission is keeping the engine revs up, there is no fuel being injected at all.

biko

Coasting - rolling downhill or approaching a junction with the car out of gear - is inadvisable because the driver doesn't have full control of the vehicle, though it used to be quite a common practice to save fuel.
* You lose the ability to suddenly accelerate out of tricky situations.
* You lose engine braking which takes some of the load off the brakes on down hill stretches and helps to avoid brake fade - overheated brakes require harder pedal pressures to stop the vehicle.

These days, coasting is still inadvisable and changes in vehicle fuel systems mean it won't save you fuel either.

Old car with carburettor - take your foot off the accelerator pedal with the car in gear and fuel is still drawn through into the engine. Fuel savings could be made by coasting out of gear.
Modern car with electronic engine management - fuel and ignition systems are effectively combined and controlled by one Electronic Control Unit (ECU). Take your foot off the accelerator and the ECU cuts the fuel supply to the injectors anyway so there's nothing to be gained by coasting.
Modern diesel engines - these also have the ability to shut off the fuel when you take your foot off the accelerator.

In February 2008, fifty AA employees took part in an eco-driving experiment in conjunction with Auto Express magazine. Each drove normally for the first week and then applied our advice (below) to see how much they could save in the second week.
The group saved an average 10% on their weekly fuel bill with the best achieving an incredible 33% saving!
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