OH FFFFFFFS !!!!!!!! ARRRGGHHH !!!!

monquixote

Sporky said:

The engine is not there to slow the car down! Brake pads are far more replaceable and far more effective.

What's wrong with engine braking? 

I've always been told it was a good thing as it reduces fuel consumption and brake wear?

Unless you thrash the clutch I don't see what harm it does. 

Phil_aka_Pip

I think @Sporky was arguing against relying on engine braking to slow you down to keep you out of trouble when a dab on the brake pedal would be far more appropriate.

[Deleted User]

Emp_Fab;18194" said:

 one of my exes used to work in the 'cherished marks' dept of the DVLA.  Part of her job was to think of rude number plates and enter them into the computer as 'never to be issued' numbers.  They called them 'skid marks'.

I know someone who wanted to buy P155 OFF. Apparently that was on the 'never issued' list....

Sporky

Phil_aka_Pip said:

I think @Sporky was arguing against relying on engine braking to slow you down to keep you out of trouble when a dab on the brake pedal would be far more appropriate.

Yup. Or in the sense of changing down to use the engine to make significant reductions in your speed rather than use the brakes. This is bad practice for two reasons; firstly it wears out the engine rather than the cheaper-and-easier-to-replace brake pads and discs, and secondly it means your brake lights don't illuminate so there's less visual clue to those behind you that you're slowing down.

Just letting off the accelerator and letting the car gradually slow under engine braking is ok.

ICBM

monquixote said:

Sporky said:

The engine is not there to slow the car down! Brake pads are far more replaceable and far more effective.

What's wrong with engine braking? 

I've always been told it was a good thing as it reduces fuel consumption

Not in my car it doesn't.

I got really a bit OCD about this when fuel got properly expensive a few years ago, and deliberately compared different driving styles. Keeping the car in top gear and using the brakes to slow down gave better economy than engine braking in lower gears. Obviously that does wear out the brake pads faster though, so it's maybe not quite so clear which is cheaper.

It's certainly better than continuing to use the accelerator to maintain high speed and then having to brake when you're too close - as you see a lot of people in the outside lane doing, that's a sheer waste of fuel - but if you need to slow down to a stop, even over a long distance, braking is more economical.

Sporky

I've read that that is largely due to the cleverness of modern engine control units - with no throttle and a high gear and moderate to high speed, they completely shut down the fuel feed. In a lower gear they maintain some fuel feed to prevent the engine from stalling.

Or something like that.

Myranda

Sporky said:

I understand engine braking, I just don't think it should be used as an evasive tactic! I've been driving long enough to remember (but not fondly) manual chokes. Also wondering what the sixth gear was for the first time I met one.

While I was tipsy when writing last night, I did mean engine braking as well as braking braking... sure the pads are better, but pads and engine in combination should be better still.

OK I'm slightly biased as I ride a bike, and if I drop a couple of gears too fast engine braking can lock the rear wheel and I'd be damnably shocked if my weedy back brake ever did that... 

Phil_aka_Pip

Just as well Myranda. Back brakes usually get you into more trouble than they get you out of.

Sporky

Myranda said:

While I was tipsy when writing last night, I did mean engine braking as well as braking braking... sure the pads are better, but pads and engine in combination should be better still.

Not really in a car - as ICBM says, the brakes can easily apply enough force to get the ABS working, so there's no need for engine braking as well (which applies far less force).

Using engine braking can be more effective on slippery surfaces when you just want to control speed - particularly off road or on snow or ice - precisely because it prevents the wheels from locking.

ICBM

Myranda said:

While I was tipsy when writing last night, I did mean engine braking as well as braking braking... sure the pads are better, but pads and engine in combination should be better still.

No, because once you get to the point the tyres can't grip it makes no difference. At best it's no better than pads alone.

At worst in really extreme cases, engine braking can have the opposite effect - the engine can slow the wheels enough that they're effectively almost locked, which will stop the ABS working properly since it relies on releasing the wheels to let the tyres regain grip. You have to get the clutch down and let the electronics handle the braking, to stop in the shortest possible distance. (Of course this does only apply to cars with ABS.) That probably sounds like 'not skilled driving' since it basically means abandoning full control and letting the technology take over, but it really is the quickest way to stop.

Engine braking is for gently slowing the car down without wearing the brake pads, and controlling speed - not for actually stopping.

Sporky

I have read, but am not quite 100% convinced, that in a car with ABS the fastest way to stop on a road is to simply stamp on the pedal with as much force as possible and let the ABS do the work. I can't work out if this is likely to be true or not - I'm pretty sure it's not the case on snow or anything else full-on slippery, but on a normal or wet road I can see how it could be true.

Phil_aka_Pip

I suspect it's because the ABS can cadence-brake faster than a human can.

RocknRollDave

snakemanStoo said:

Have you tried pressing that pedal in the middle occasionally?

This reminds me of when I went to the bodyshop with an ex-colleague* to collect a loan car with him whilst his car was in for work, and he'd had so many little bumps and prangs that the guys in the bodyshop would walk through reception and without even looking up would say "Oh, hi Derek#...." as he was there so often. The woman who was sorting out the paperwork had to do the usual quick run through of the specifics of the car they were loaning him - you know "the stalk for the wipers is on this side, your headlight controls are here", that kind of thing, and she even went "and THIS pedal here is the BRAKE, Derek"...I LOL'd


*I say ex-colleague...he's also our current drummer...go figure...
# I have changed Simon's name here to protect his anonymi..oh bollocks.

ICBM

Sporky said:

I have read, but am not quite 100% convinced, that in a car with ABS the fastest way to stop on a road is to simply stamp on the pedal with as much force as possible and let the ABS do the work. I can't work out if this is likely to be true or not - I'm pretty sure it's not the case on snow or anything else full-on slippery, but on a normal or wet road I can see how it could be true.

It definitely is true, so much so that some manufacturers now fit 'Emergency Brake Assist' which essentially takes over if you press the brake pedal hard enough - most drivers apparently don't actually press the pedal hard enough manually, either because they're not used to doing it or because the pedal judder when the ABS kicks in makes them back off.

There's no way a human can apply and release the brakes at the speed ABS does even if they could detect the exact point of skid precisely enough - and that's even with a single ABS system, let alone independent per wheel.

Sporky

Thanks chaps - it seemed pretty plausible, I was just wondering if (assuming great driver skill) you'd actually stop faster by applying just the right level of pressure to get the 5% slip or whatever it is that is the greatest force between road and tyres. Difficult in practice, I imagine!

mike_l

I was once told by a bus driver that they're trained to "ride the car in front" rather than slam the brakes on as it reduces the amount the passengers get thrown around in a collision.

 

@Sporky, I wouldn't recommend stamping on a brake pedal on anything other than a dry road. Not that I've had brown-trouser moments whilst doing that or anything you understand.....

ICBM

I remember seeing a demo on one of the car shows years ago where they showed that the shortest possible stopping distance was actually achieved by deliberately spinning the car - because that uses up energy, which has to come out of the forward motion - but that it requires enormous skill and you'd never manage that under real road conditions no matter who you were.

monquixote

Sporky said:

Yup. Or in the sense of changing down to use the engine to make significant reductions in your speed rather than use the brakes. This is bad practice for two reasons; firstly it wears out the engine rather than the cheaper-and-easier-to-replace brake pads and discs, and secondly it means your brake lights don't illuminate so there's less visual clue to those behind you that you're slowing down.

Is that actually true, and if so what does it wear?

As far as I'm aware moderate engine braking doesn't introduce additional wear as it's just a result of back pressure in the exhaust system, or air intake. I know if you go silly with it like changing into first at 70 you shred the clutch, but assuming you don't do that I don't see what it is hurting. 

chillidoggy

Being of the old school, I was taught to use engine-braking wherever I could, and brakes where necessary. I still do this today, it's a habit I've never seen the need to change. The Mondeo front discs have just been changed at 90,000 miles, which is fine by me, and speaking as an engineer, I don't hold with the view that engine braking places any undue strain or wear on the engine, or gearbox, as long as it's done properly.

I do know that things have altered in the years since I took my driving test, though. Apparently there's no longer a need to have a bloke carrying a red flag walking in front of the car.

mike_l

CHilli's right, normal engine braking won't harm anything. Only if (as Monquixote said) if you change into 1st at 70, you'll damage the clutch (i've seen one destryed*), potentially over -rev an engine, or damage the CV joints on driveshafts.

 

*as in both plates shattered.