The Dangers of Coasting

[.R2D2]

The OH is always coasting and I keep on at her that its dangerous. She ask's why and I said you're losing control of the car, it becomes sloppy almost. But that doesnt seem to do the job, now I know its wrong but I just cant seem to get my point across, how else can I go about it?

[Superhoop]

Ask her if she did it on her driving test...., and if not why not - She'll probably tell you that she was told not to by her instructor

[shakotan]

Whatever you do, don't look up hypermiling technique, as some of them advocate engine-off coasting and engine-off braking!

[J4CKO]

I dont do it as I too had it drummed into me but I think the advice comes from a time when cars didnt have massive servo assisted disk brakes and used engine braking more, really whether your engine is connected to the wheels on a modern car doesnt make much difference to the safety aspect, its just poor driving and a bad habit.

[balls-out]

doogz said:

Take her a drive in her car, batter it's melt in, til the brakes are f*cking cooked, then show her the difference between an emergency stop with and without engine braking.

P.S. i don't actually advise this, it could end badly.

I think you wil find most car's brakes are quite happy without engine braking. Very few people manually shift an auto into low to provide engine braking and most cars come as auto wihtout uprated brake.
Steep alpine passs excepted of course

Whilst the IAM don't recommend coasting, they are quite happy for you to slow down from high speeds and not change gear - juast change into neutral when stopped. the engine breaking in 4th is minimal once below 40-50 I'd say

Edited by balls-out on Friday 24th September 08:58

[ExPat2B]

There is nothing wrong with coasting, provided you are thinking sufficently far ahead.. In fact, if you have your right foot covering the brake, it can speed up reaction times.

[saaby93]

ExPat2B said:

There is nothing wrong with coasting, provided you are thinking sufficently far ahead.. In fact, if you have your right foot covering the brake, it can speed up reaction times.

Unless you panic in an emergency move it across and slam the clutch to the floor

[Alfa numeric]

ExPat2B said:

There is nothing wrong with coasting, provided you are thinking sufficently far ahead.. In fact, if you have your right foot covering the brake, it can speed up reaction times.

Couldn't agree more- my car's got quite a strong tickover so if I'm rolling up to a line of slow moving or stationary traffic I'll knock it into neutral and roll up to it.

Didn't SAAB have some sort of freewheel mechanism in the 70's?

[balls-out]

Alfa numeric said:

ExPat2B said:

There is nothing wrong with coasting, provided you are thinking sufficently far ahead.. In fact, if you have your right foot covering the brake, it can speed up reaction times.

Couldn't agree more- my car's got quite a strong tickover so if I'm rolling up to a line of slow moving or stationary traffic I'll knock it into neutral and roll up to it.

Didn't SAAB have some sort of freewheel mechanism in the 70's?

Might have been earlier? Otherwise the 2 stroke engine, staved of its oil mixed in the petrol might seize.

[HellDiver]

Besides, you use more fuel coating in neutral than you do with the car in gear and no throttle. With the car in neutral, the engine uses fuel to continue idling, with no throttle and still in gear the car uses no fuel at all.

[eybic]

HellDiver said:

with no throttle and still in gear the car uses no fuel at all.

How can an engine that runs on fuel not use any at all and keep running?

[HellDiver]

eybic said:

HellDiver said:

with no throttle and still in gear the car uses no fuel at all.

How can an engine that runs on fuel not use any at all and keep running?

What? Think about it. Read what I said carefully. Think about it again. No throttle, in gear, the wheels keep the engine turning, don't they?

[Dogwatch]

ExPat2B said:

There is nothing wrong with coasting, provided you are thinking sufficently far ahead.. In fact, if you have your right foot covering the brake, it can speed up reaction times.

Maybe a bit irritating but don't see it as dangerous (or even fuel saving). I have heard this before and think some people confuse 'reduced control' with 'out of control'.

[CraigyMc]

I always thought you should be braking in gear because that way there's a connection (via the diff) between one wheel and another?

No idea if EBD just solves this as an issue though.

C

[Hedders]

HellDiver said:

eybic said:

HellDiver said:

with no throttle and still in gear the car uses no fuel at all.

How can an engine that runs on fuel not use any at all and keep running?

What? Think about it. Read what I said carefully. Think about it again. No throttle, in gear, the wheels keep the engine turning, don't they?

I assumed that if the engine reports that it is turning at 3000 rpm it will be using more fuel than if it reports it is turning at 1000rpm. I could be wrong?

[ExPat2B]

The Crack Fox said:

ExPat2B said:

There is nothing wrong with coasting, provided you are thinking sufficently far ahead.. In fact, if you have your right foot covering the brake, it can speed up reaction times.

Assuming the hazard requires you to stop, not accelerate, otherwise you're fooked.

If there is a junction or other hazard that may require acceleration then you should be in gear. However the number of hazards that actually require acceleration is approaching zero, and I think that if you are required to accelerate to get out of danger you have done something wrong further up the chain.

[750turbo]

Hedders said:

HellDiver said:

eybic said:

HellDiver said:

with no throttle and still in gear the car uses no fuel at all.

How can an engine that runs on fuel not use any at all and keep running?

What? Think about it. Read what I said carefully. Think about it again. No throttle, in gear, the wheels keep the engine turning, don't they?

I assumed that if the engine reports that it is turning at 3000 rpm it will be using more fuel than if it reports it is turning at 1000rpm. I could be wrong?

At this point the car would be "powering" the engine, no fuel being used. Ticking over at 1,000rpm, would use "some" fuel.

[HellDiver]

You are wrong. Freewheeling the engine with no throttle on the majority of fuel injected cars will stop the fuel injectors completely.

Even the old SPI Vauxhall engines from the late 80's did it (like the Cavalier 20SEH) - basically anything with a Bosch Motronic back then.

[ExPat2B]

Hedders said:

HellDiver said:

eybic said:

HellDiver said:

with no throttle and still in gear the car uses no fuel at all.

How can an engine that runs on fuel not use any at all and keep running?

What? Think about it. Read what I said carefully. Think about it again. No throttle, in gear, the wheels keep the engine turning, don't they?

I assumed that if the engine reports that it is turning at 3000 rpm it will be using more fuel than if it reports it is turning at 1000rpm. I could be wrong?

On a modern fuel injected car, if the car is in gear, decellerating against the engine, then effectively the engine is just an airbrake, no fuel is injected at all.

[Munter]

Hedders said:

HellDiver said:

eybic said:

HellDiver said:

with no throttle and still in gear the car uses no fuel at all.

How can an engine that runs on fuel not use any at all and keep running?

What? Think about it. Read what I said carefully. Think about it again. No throttle, in gear, the wheels keep the engine turning, don't they?

I assumed that if the engine reports that it is turning at 3000 rpm it will be using more fuel than if it reports it is turning at 1000rpm. I could be wrong?

What 50% more of nothing. Nothing.

A modern fuel injected engine cuts the fuel completely if your foot is off the throttle and the engine is not stalling. The momentum of the car turns the wheels, and they turn the engine. Air still go's in and out but no fuel is injected as it's not required.