Fuel efficient driving.

cyclonebri1

Inactive wrote: »

So how do you drive down hill to a red light?

I drive down using my brakes to the red light using my brakes.

Your taking it too literally, of course you have to brake down a hill to a dead stop. The art is to brake more gently, but under those conditions I would use engine braking as all fuel would be shut off.

I would try, road conditions allowing, to arrive at the lights without the need to actually stop, ie by approaching slower, untill the light changed.

I also belief in carrying corner speed wherever possible, hence my never ever brake comments. I probably drive much faster round clear corners than most people I know, but am generally a steadier driver in overall speed terms.


sorry myhoose, read your post after this reply, not trying to crib;)
All has to be judged sensibly of course with concern for other troad users.

I get my best economy on the motorway, but that's simply because nothing is usually moving at more than 50mph;);)

Inactive

cyclonebri1 wrote: »

Your taking it too literally, of course you have to brake down a hill to a dead stop. The art is to brake more gently, but under those conditions I would use engine braking as all fuel would be shut off.

I would try, road conditions allowing, to arrive at the lights without the need to actually stop, ie by approaching slower, untill the light changed.

Surely the same amount of fuel is used if you are braking or allowing the engine to slow the vehicle on a downhill run to a red light, I agree with your comment about trying to avoid actually stopping, but of course by braking you can time that more accurately.

jeferey

Inactive wrote: »

Surely the same amount of fuel is used if you are braking or allowing the engine to slow the vehicle on a downhill run to a red light...

No - if you engine brake in most modern cars, i.e. leave it in gear and lift off the accelerator, a modern fuel-injected car will shut off the fuel completely.

Inactive

jeferey wrote: »

No - if you engine brake in most modern cars, i.e. leave it in gear and lift off the accelerator, a modern fuel-injected car will shut off the fuel completely.

Am I missing something? I am leaving it in gear with my foot off of the accelerator, I am just using my brakes as well.:huh:

cyclonebri1

Inactive wrote: »

Am I missing something? I am leaving it in gear with my foot off of the accelerator, I am just using my brakes as well.:huh:

It is a close call.

But using your brakes "as well" increases the rate of decellaration, ie, it loses kenetic (paid for) energy.

If you judge it correctly, and here is the rub, it doesn't matter how you slow/stop, the end result is the same.

In the vein of my earliest post, never ever brake or more likely, "slow down"

Good to see so much thought going into a general forum post:T:T
I think all this makes sense and I'm sure most will figure this

skiddlydiddly

Inactive wrote: »

Am I missing something? I am leaving it in gear with my foot off of the accelerator, I am just using my brakes as well.:huh:

Plus cars(hybrids excluded) don't miraculously run on fresh air when you lift off the throttle.It still needs fuel or it will stall.

daveyjp

skiddlydiddly wrote: »

Plus cars(hybrids excluded) don't miraculously run on fresh air when you lift off the throttle.It still needs fuel or it will stall.

If the car is moving downhill in gear and you lift off the fuel flow is cut off completely. No fuel is required as the engine is being turned by the wheels turning so it won't stall.

Fuel will be added when rpm drops below a certain level to prevent stalling.

Next time you accelerate the injection system starts adding fuel again.

My current car does "stall" when you stop as it cuts the engine to save fuel!

cyclonebri1

skiddlydiddly wrote: »

Plus cars(hybrids excluded) don't miraculously run on fresh air when you lift off the throttle.It still needs fuel or it will stall.

As above from Davey, the threshold is usually at about 1000rpm in any gear.

Easy to demonstrate, find a quiet steep down hill and engage top gear at about 20mph. You will feel the car accelerating with no throttle untill it reaches the point where the fuel is shut off and the engine braking comes into play.;)

skiddlydiddly

Yes I am getting coasting and free-wheeling mixed up.Interesting how rolling down a hill in neutral uses more fuel than being in gear when you'd maybe expect the drag of the gearbox to increase fuel used.

Strider590

skiddlydiddly wrote: »

you'd maybe expect the drag of the gearbox to increase fuel used.

In carburettor powered cars yes, because the fuel supply is never shut off, it continues fuelling as if at idle speed.....
Selecting neutral and rolling down a hill has zero effect as the engine consumes as much fuel at idle as it does under reversed load (so to speak).

But modern cars, leave it in gear and the ECU cuts ALL fuel to the engine but keeps the ignition running. Take the car out of gear and the ECU will continue to fuel as it would for idle.