Using the gears to slow a car down Watch

PervyPete
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I'm trying to hypermile my diesel.

When I come off a motorway this is my procedure:

Indicate to come off, just before the slip road, cancel my cruise control (60mph) and let the car decelerate to 50 mph, then drop to 4th gear, let the car decelerate to 40 mph, then drop to 3rd gear, then when at 25 mph just coast to 0 mph.

Is it damaging my gearbox to use the gears rather than the brakes to slow the car down ?
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Camoxide
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slow down in fifth and then rev match for third gear

You don't want the action of putting it into gear slowing the car down.
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honeywhite
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(Original post by PervyPete)
I'm trying to hypermile my diesel.

When I come off a motorway this is my procedure:

Indicate to come off, just before the slip road, cancel my cruise control (60mph) and let the car decelerate to 50 mph, then drop to 4th gear, let the car decelerate to 40 mph, then drop to 3rd gear, then when at 25 mph just coast to 0 mph.

Is it damaging my gearbox to use the gears rather than the brakes to slow the car down ?
I wouldn't say it's damaging, but it does waste fuel. Still, braking with the brakes wears them down, and brakes are more expensive than fuel.
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Camoxide
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Brakes are cheap. You can get a set of front pads for like £50
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Alfissti
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Brakes are cheaper and easier to replace than a clutch
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ak_93
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just keeping it in 5th untill you need to acceleratae again (i.e, you get to the roundabout or w/e ) will be fine, and least wear on the clutch.

as long as you are in "a gear" and the accelerator is not pressed, the fuel supply to the engine is cut off.
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PervyPete
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(Original post by ak_93)
just keeping it in 5th untill you need to acceleratae again (i.e, you get to the roundabout or w/e ) will be fine, and least wear on the clutch.

as long as you are in "a gear" and the accelerator is not pressed, the fuel supply to the engine is cut off.
Second point is incorrect. 5th gear is geared to 3000k per 100 mph (diesel). If I try and cruise at 40 mph in 5th then the engine will use fuel to stop itself stalling, hence the drop to 4th to stop this happening
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PTMalewski
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Engine is a basic car brake.
In motorsport and correct normal driving engine should be connected with transmission as long as possible. It does not applies only in gentle driving during low speed deceleration when sometimes it's better not to shift lower than to 3rd gear.

(Original post by honeywhite)
I wouldn't say it's damaging, but it does waste fuel. Still, braking with the brakes wears them down, and brakes are more expensive than fuel.
As far as I know it doesn't. In gasoline engines, computer turns the injectors off during breaking with engine so it saves fuel. In diesel power is adjusted by percentage of fuel in the air, so there is very little or no fuel in the air during deceleration with engine.

(Original post by Alfissti)
Brakes are cheaper and easier to replace than a clutch
Use heel and toe technique- then the cluth does not suffer. You can do this in any car, only the foot moves are different depending of what kind of pedals do you have.

Car with pressed cluth or neutral gear is also very unstable and cannot be quickly controlled when something unexpected happens. Engine is a main brake and also a second steering system.
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Camoxide
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The engine will start to inject fuel once the revs hit about 1000. You can feel this when you let slow to a low speed in 5th and the revs will bump up slightly after dropping bellow 1000
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JC.
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All this ****e about clutches being cheaper to replace than brakes is a total red herring.

I always come down the box and I've never had to replace a clutch through my own driving style - including cars I've kept for 80k miles.
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PTMalewski
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(Original post by Camoxide)
The engine will start to inject fuel once the revs hit about 1000. You can feel this when you let slow to a low speed in 5th and the revs will bump up slightly after dropping bellow 1000
Correct, it's usually 1200rpms for gasoline. Actually, already some carburettor engines had deceleration fuel cut off.


(Original post by JC.)
All this ****e about clutches being cheaper to replace than brakes is a total red herring.
Quite agree

(Original post by JC.)
I always come down the box and I've never had to replace a clutch through my own driving style - including cars I've kept for 80k miles.
No suprise there. Modern cars such as Passat are designed to die after 125k miles, while older generations had no clear limit that would make repairs unprofitable, while lots of engines from 80ties could go over 312k miles without capital repair (if treated properly), and after that you could repair it with oversize parts.
Cluth should survive 100k miles at least.
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gbduo
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I always come down the gears sequentially and use engine braking. I just got 30k miles out of a set of brake pads and I'm still on the original clutch at 80k miles. A clutch only wears when it is slipping.

Not bad on a 300hp modified sports car...

So yes, engine brake, not only for fuel efficiency but you have more control and its more mechanically sympathetic.

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IntriguedUser
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I thought the ECU stopped fuel flow to the injectors if there's no load on the pedal and you're in gear, using the cars momentum to turn over the engine. Being in neutral means the engine has to use fuel to keep it idling.
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gbduo
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(Original post by IntriguedUser)
I thought the ECU stopped fuel flow to the injectors if there's no load on the pedal and you're in gear, using the cars momentum to turn over the engine. Being in neutral means the engine has to use fuel to keep it idling.
Yes, spot on.
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