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Author Topic: Is it better to use the engine to decelerate?  (Read 9049 times)

Offline Geezer

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Re: Is it better to use the engine to decelerate?
« Reply #25 on: 27/04/2012 20:37:39 »
"Actually, that would reduce your stopping distance if you could ever get the tires to spin backwards - it would work like a dragster in reverse."
No it would not spinning the wheels would lead to reduced adhesion the best braking effect is acheived when the wheels are are still rotating at a rate appropriate for the speed of the vehicle.




That's true when only a braking force is being applied, but when the wheels are spinning in the opposite direction, you are applying a thrust in a direction opposite to the direction of travel. It works like a reverse thruster of sorts. (It probably would make the vehicle incredibly unstable too!)
« Last Edit: 27/04/2012 21:59:45 by Geezer »
 

Offline CZARCAR

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Re: Is it better to use the engine to decelerate?
« Reply #26 on: 28/04/2012 15:15:22 »
does the engine/tranny fluids experience a beneficial overflush due to downgearing?
 

Offline CycleGuy

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Re: Is it better to use the engine to decelerate?
« Reply #27 on: 04/08/2015 03:03:54 »
"Actually, that would reduce your stopping distance if you could ever get the tires to spin backwards - it would work like a dragster in reverse."
No it would not spinning the wheels would lead to reduced adhesion the best braking effect is acheived when the wheels are are still rotating at a rate appropriate for the speed of the vehicle.

Actually, the best traction is achieved with some wheel slippage. Racers use this knowledge all the time. The problem is, after you reach this maximum traction:wheel slippage ratio, the traction falls off, which puts you into a slide (in a turn) or just smokes your tires (in straight line acceleration) or puts you into a skid (when braking). The trick is to ride as close as possible to the ideal ratio, without going over it.
newbielink:http://physics.stackexchange.com/questions/5838/why-does-a-tire-produce-more-traction-when-sliding-slightly [nonactive]
« Last Edit: 04/08/2015 03:12:59 by CycleGuy »
 

Offline wolfekeeper

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Re: Is it better to use the engine to decelerate?
« Reply #28 on: 05/08/2015 18:10:04 »
When I am driving my car and approach traffic lights when they are red, I often change down gears and allow the engine to 'do the braking' hence preserving my brakes. However, when changing down gears and subsequently slowing down the RPM (revolutions per minute) increase, though I am not pressing the accelerator. Will this still increase my fuel consumption, eventhough I am slowing down.
Should I avoid doing this practice and just apply the brakes earlier and wear them out sooner?

On virtually all modern cars, revving the engine up like this uses NO fuel at all; there's a fuel cut off that kicks in when you have your foot off the accelerator and when the revs are just above idle.

If you're slowing down, what you should do is keep the highest gear you can so as to keep the revs above about 1000 rpm and start slowing as early as possible.

It's surprising how much fuel you will save doing this-it can improve your mpg by maybe 3 or 4.

Using the brakes usually means your foot isn't on the accelerator, so the same thing applies, however the fuel cut-off will be happening for a shorter time.

You can even do this with automatics, if you use the gear selector, but I wouldn't recommend you try it if there's someone behind you or on a bend; braking can be a bit abrupt!
 

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Re: Is it better to use the engine to decelerate?
« Reply #28 on: 05/08/2015 18:10:04 »

 

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