Coasting in neutral

kdevitt

gatecrash wrote: »

On the hill i was referring to I HAD to use the brakes. If I had driven (in gear) down that hill i wouldn't have been going quite so fast

Sounds like your example was just pure bad driving - you let the car roll to 60mph - of course its going to feel like its getting away from you. :rolleyes:

AckwelFoley

--amadeus-- wrote: »

I'm sorry but you have totally lost me here

How will the gearbox be turning faster than it should because it's being driven by the wheels rather than the engine? The gearbox will be working at exactly the same speed as if the clutch was engaged will it not, at whatever speed it should be relative to the wheel speed, regardless of where the motive force is from.

And why does the difference between engine speed and gearbox speed make any difference? The OP asked about coasting in neutral so there is no connection between teh gearbox and teh engine so thier relative speeds are irrelevant, aren't they?

As for re-selecting a gear you'd blip the throttle before engaging to match revs and road speed I assume.

Couple of points - I can think of absolutley no way that coasting a car can damage it, as long as you try to match revs before re-engaging the gearbox. Coasting in neutral should not be confused with slipping (or riding) the clutch, where you depress the clutch while gears are engaged so reduce the torque going from the engine to the wheels. This is a very bad habit and causes a huge amount of wear to the clutch pad.

Secondly there is a huge difference between free wheeling down a steep hill (which is dangerous) and popping teh car into neutral so it can roll forward in stop start town traffic.

Ladies and gentlemen.

This is the only post that makes sence in this thred.
just to add, when you are driving on a road, the engine DOES NOT CONTROL BRAKING.. the breaks do. Where the engine helps is holding control going down hill etc..

If in doubt just read Amaeus's post again

AckwelFoley

Coasting will save fuel, but its a bad habit.



You will fail your dribing test of you do it

milltown

--amadeus-- wrote: »

I'm sorry but you have totally lost me here

How will the gearbox be turning faster than it should because it's being driven by the wheels rather than the engine? The gearbox will be working at exactly the same speed as if the clutch was engaged will it not, at whatever speed it should be relative to the wheel speed, regardless of where the motive force is from.

And why does the difference between engine speed and gearbox speed make any difference? The OP asked about coasting in neutral so there is no connection between teh gearbox and teh engine so thier relative speeds are irrelevant, aren't they?

As for re-selecting a gear you'd blip the throttle before engaging to match revs and road speed I assume.

Couple of points - I can think of absolutley no way that coasting a car can damage it, as long as you try to match revs before re-engaging the gearbox. Coasting in neutral should not be confused with slipping (or riding) the clutch, where you depress the clutch while gears are engaged so reduce the torque going from the engine to the wheels. This is a very bad habit and causes a huge amount of wear to the clutch pad.

Secondly there is a huge difference between free wheeling down a steep hill (which is dangerous) and popping teh car into neutral so it can roll forward in stop start town traffic.

Just for the sake of being pedantic, and for the benefit of Snyper, Amadeus and Vtec, who are all wrong in their own little ways:

When coasting as described previously in this thread, unless the clutch pedal is depressed, the gearbox and engine are still very much connected. The output shaft of the gearbox is turning at the wheel speed divided by the final drive ratio, while the input shaft is turning at engine speed. There could be a large difference between the two shaft's speed's. When a car is driving normally in a gear, the drive is transmitted through the input shaft, to the layshaft, through the selected gear to the output shaft and final drive. All other gears are freewheeling on the output shaft but driven by the layshaft at engine speed.

Only a proper lunatic would be coasting at speeds that would cause these shaft speeds to exceed their normal operating range.

Driving in gear with the clutch depressed will not wear your clutch plate. It may shorten the life of your release bearing but that's about it.

My opinion: It's not going to damage your car but it's not a good idea. Drive smoothly and read the road and other drivers ahead and you'll improve your fuel economy to the point where there's neglible gain to be made from coasting.

Terrontress

It may not damage the car but it is dangerous. It is the drive from the transmission that keeps you on the road. Same reason why you should accelerate round bends.
And to suggest BMW would recommend doing this is a nonsense.

kdevitt

Terrontress wrote: »

It may not damage the car but it is dangerous. It is the drive from the transmission that keeps you on the road. Same reason why you should accelerate round bends.
And to suggest BMW would recommend doing this is a nonsense.

I wasn't suggesting BMW recommended it - I was stating it as fact, which it is.

So tell me a bit more about your accelerate around the corners theory - specifically in relation to FWD cars.

PRND

kdevitt wrote: »

I wasn't suggesting BMW recommended it - I was stating it as fact, which it is.

So tell me a bit more about your accelerate around the corners theory - specifically in relation to FWD cars.

I think he's right.

Read this

http://www.cumbria.police.uk/bikesafe/html/cornering_car_drivers.html

First paragraph.

And when you read that; read this

http://driving.timesonline.co.uk/tol/life_and_style/driving/car_clinic/article3082470.ece

Fifth question down.

I'd be interested if you could provide a verbatim quote from the BMW manual. Maybe you have misread it. I don't doubt you are trying to tell the truth.

copacetic

kdevitt wrote: »

I wasn't suggesting BMW recommended it - I was stating it as fact, which it is.

So tell me a bit more about your accelerate around the corners theory - specifically in relation to FWD cars.

have you got anything to back up your 'fact'? Only in commas as I'm sure like me you see plenty of posts stating things are facts on boards, generaly people like to see the proof themselves, not believe random people on the interweb. (and thats a fact!)

I haven't heard this before and have had a bmw previously with no mention of this in the manual that I remember.

Terrontress

I don't believe it to be fact. Unless it was a misprint but even still, the op should not do it.

And I don't need a website to tell me not to decelerate on a bend. Anyone who actually thinks about what they're doing while driving would know. Maybe devitt has only driven Lincoln Town Cars or something else that's like driving a pillow

here.from.day.1

Just to the posters who said that coasting can save on fuel consumption, when you coast (in gear btw, never tried in neutral) yes the MPG goes up but as you coast you lose speed and then to get back to the speed you were cruising at you would need accelerate harder (bringing the MPG way down) than if you hadn't coasted, thus cancelling out any fuel saved, no?

--amadeus--

milltown wrote: »

Just for the sake of being pedantic, and for the benefit of Snyper, Amadeus and Vtec, who are all wrong in their own little ways:

Wow, someone even more pedantic than me!

Of course you're right - the layshaft will still be spinning at engine speed, but that's getting a bit arcane and technical for this discussion isn't it? For the purposes of simplicity there is no connection between engine and wheels when the car is in neutral and the fact that they (and by extension different gearbox elements) are spinning at different speeds is not going to cause any damage, which is the point I was trying to make.

I'm afraid I'll disagree with you on the amount of wear that riding the clutch causes. It can and does damage the clutch pad, both through excessive wear of the friction coating and through the excessive temperature that can build up within a heavilly slipped clutch ("cooking the clutch") which also damages the coatings. Again you are right on the damage it will cause to the release bearing which is not intended for continual use - it's bad full stop!

I can't see any reason why somoeone would coast in nuetral in free flowing traffic, driving in the right gear and maintaining a constant speed will be better than accelerating, coasting and accelerating (as well as being safer). But rolling to a halt in city driving isn't dangerous.

And just to prove that I am equally pedantic (;)) you shouldn't "accelerate around a bend". It's better to be "slow in, fast out", brake on the approach and accelerate only from the apex of the bend. In normal driving holding a constant throttle will keep the car balanced and is the most "sensible" way to drive.

Terrontress

To be even more pedantic, maintaining constant speed is accelerating relative to the car's natural state.