Engine Braking

DaMonk

Hi, i recently remapped my VW and am very conscious of trying to keep the clutch in one piece! just wondering if cycling down through the gears when stopping is bad for the clutch and would I be better off coasting to save the clutch?

HungryJoey

What engine did you have remapped that has you so worried? Why not just have an uprated clutch put in if you are that worried about the extra power harming the OE clutch.

2 Espressi

You're not going to do much damage to the clutch as long as you let the revs drop fairly low before downshifting, and rev matching:

wrote:

REV MATCHING is a driving technique for shifting a manual transmission smoothly. One simply memorizes approximately how many RPMs different the various gears are from one another at the same speed, and then matches the engine's revs with the gear they are shifting in to. When upshifting, you just let the revs drop and slip into gear. When downshifting, you tap the throttle (or stomp on it depending on how long it takes to rev up.) This is often referred to as 'blipping' it. This works easily primarily because of the syncromesh gears in your transmission; if your transmission does not have them, this is very, very difficult to do without grinding. Even so, it takes the right touch.

For example, in one car the gears might all be approximately 1,000 RPM apart at the same speed. When downshifting from third to second, for example, you would apply accelerator pressure to raise the engine RPMs by 1,000 (say, from 3,000 to 4,000) and make your shift. You can then use engine braking to reduce your speed.

This practice results in reduced brake wear, less of a lurch when shifting from a higher gear to a lower one, less clutch slippage when shifting from a lower gear to a higher one, and a smoother shift without having to slip the clutch so much.

In auto racing, one often uses the more advanced form of this activity, heel-toeing (Alternately heel-toe braking or heel-toe downshifting) in which one's heel is on the brake pedal, decelerating, while the toe is on the gas pedal, accelerating. This allows the use of both the brakes and the engine to perform braking.

Mr.David

Hi,

When I learned to drive I was taught to cycle down through the gears and combine engine braking and hydraulic breaking! However, I now work for Jaguar and have since done a few advanced driving courses. The instructors teach you not to cycle instead to brake down to the point at which the car feels as if it will soon cut out and then clutch and change to the next gear you need. i.e. Brake from 60mph (5th gear) down to 20mph (still 5th) clutch and change to 2nd for the corner.

This saves the clutch (less use) and allows you to have both hands on the wheel for control and 100% concentration on the road ahead. Engine braking is just a throwback to the days of huge trucks with brakes that were insufficient. Modern cars do not require engine braking.

Hope that helps!!

Mr.David

Regarding Rev matching, the easiest way to try it is not to let the accel out when downchanging. i.e. travelling at 35mph in 4th, with your foot on the accelerator (not gaining momentum just staying constant) clutch in and change gear swiftly (keeping foot on throttle the whole time). This has the effect of blipping the revs to match the required revs for the lower gear. Its much smoother once you get the hang of it.

Once you have mastered that you can try powershifting i.e. changing gear without clutching at all, it only requires you to match revs carefully. Its faster (was employed by rally drivers for instance) and does not damage the car as long as done well.

Alanstrainor

Always wondered about power shifting, too afraid to try it though.

green-blood

good lord lads, MECHANICAL SYMPATHY

or if you prefer WALLET SYMPATHY

Engine brekaing is all well and good, and if you can match your revs correctly go ahead, but breaks are for breaking... consider the replacemtn cost of new pads vs the cost of a new clutch... can you heel and toe??

ditto "powershifting"...on the road... when woudl that ever be neccessary (other than after a spot of engine brekaing that eh, breaks your clutch)

Zube

Mr.David wrote: »

The instructors teach you not to cycle instead to brake down to the point at which the car feels as if it will soon cut out and then clutch and change to the next gear you need.

That's what my driving instructor told me (20+ years ago), as brake pads are cheaper than clutches. However, he also told me to use all the gears on the test, as testers believed in it. Don't know what current tester thinking is.

Mr.David

As far as I know in Ireland you still should cycle down for the test but in UK they have changed it. Typical. One of the many ridiculous things they teach you!!

peasant

DaMonk wrote: »

Hi, i recently remapped my VW and am very conscious of trying to keep the clutch in one piece! just wondering if cycling down through the gears when stopping is bad for the clutch and would I be better off coasting to save the clutch?

The fact that your engine was remapped has no influence on engine braking ...after all, you're not on the gas when engine braking, so the increased power makes no difference.

What's going to kill your clutch quicker is all the heavy acceleration, now that ou have more ooomph to play with.

DaMonk

peasant wrote: »

The fact that your engine was remapped has no influence on engine braking ...after all, you're not on the gas when engine braking, so the increased power makes no difference.

What's going to kill your clutch quicker is all the heavy acceleration, now that ou have more ooomph to play with.

I know that ya. Just wondering if I'm wearing my clutch needlessly by engine breaking when I could just be breaking normally. Engine breaking is a habit by now and I hate coasting but since my clutch is going to get worn more due to remapping I'm trying to keep all other wear at a minimum.

On a side note, is it better or worse for the clutch to come off it faster when accelerating gears? From 1st for instance?

peasant

there's a golden middle between shiftiing down all the gears and coasting ...only changing gears when necessary,as described further above.

What really wears a clutch is slippage ...so be careful only to stomp back on the gas when the clutch has fully engaged when changing up.

I wouldn't worry too much about matching engine speed and gearbox speed ...that's what syncromesh is for.

Dirty_Diesel

DaMonk wrote: »

Hi, i recently remapped my VW and am very conscious of trying to keep the clutch in one piece!

I dont know what engine you have but when I remapped my PD130 passat I was told to never floor it below 1900rpm in 4th/5th/6th or the torque will wreck the clutch. My brother bought the car off me and didn't heed my advice. After a few months he had to fork out €1000 for a new clutch :mad:

DaMonk

peasant wrote: »

there's a golden middle between shiftiing down all the gears and coasting ...only changing gears when necessary,as described further above.

What really wears a clutch is slippage ...so be careful only to stomp back on the gas when the clutch has fully engaged when changing up.

I wouldn't worry too much about matching engine speed and gearbox speed ...that's what syncromesh is for.

Ya I was a bit confused as to what slippng is exactly. Am I right in saying that its accelerating while having the clutch not fully let out?

peasant

DaMonk wrote: »

Ya I was a bit confused as to what slippng is exactly. Am I right in saying that its accelerating while having the clutch not fully let out?

yepp ..that would be it.

Also, if the engine is too strong for the clutch, applying full power from the beginning would cause the clutch to slip all by itself, you've got to ease it into it, especially with a diesel that has all that low down torque.

Biro

The savings on the clutch by coasting when slowing down will be so minimal that the fuel you'd save by engine breaking might be a bigger saving. In any case coasting might only save 1000 miles on a clutch over 100,000, meaning that chances are you'll have to replace it one way or another at some point.

mickdw

The idea of slowing down on the brakes to a point where you cannot slow down anymore without stalling before changing down is a bad idea. It means you are using a lowest rpm at any given speed but as far as car control is concerned, Id certainly like to have a little revs/power available to balance the car with.

Esel

mickdw wrote: »

The idea of slowing down on the brakes to a point where you cannot slow down anymore without stalling before changing down is a bad idea. It means you are using a lowest rpm at any given speed but as far as car control is concerned, Id certainly like to have a little revs/power available to balance the car with.

It's not for when you are slowing down, it's for when you know you are coming to a stop.

ianobrien

I remember reading in a tuning guide (admittedly it was for classic Ford engines) and they were on about clutches.

They said that the strength of a clutch is due to the clamping forces of the springs on the friction forces in the clutch being stronger than the torque produced by the engine. When the engine is producing more power than originally designed, and when the torque is more that the clamping forces in the clutch springs on the friction surfaces, clutch slip results.

Oh, the clutch spring provide the force that keeps the clutch plates together. It's the friction between these plates that makes the clutch work

When the clutch is worn, the level of friction between the clutch plate & flywheel is reduced. Eventually, the level of friction is so low that the torque produced by the engine is more that the friction can handle, meaning a slipping clutch and it's time to change.

So, to make the clutch last, you minimise the wear on the friction surfaces. To do that, basically make sure that the clutch pedal is fully out before you stamp on the loud pedal, no grand prix starts and pressing the clutch doesn't wear out the clutch friction surfaces, it wears the clutch release bearing.

cyclopath2001

Interesting thread. I never understood so much about what goes on under the hood.

My driving instructor educated me in engine braking, his rationale was that you were more in control of the car than when using brakes alone. He also insisted that I tap (press) lightly on the brake pedal (no...not morse code, just engage the brake light to warn others that I'm slowing down).

Nothing annoys me more than someone dragging a car through a turn while in too high a gear.

I think the wear & tear thing depends on how gentle you are on the pedal and listening to the revs. But, I'm no advanced driver.

Mr.David

Its somewhat down to personal preference. I often brake down from 5th to 3rd for instance. Coasting should definitely be avoided and it actually uses more fuel than leaving the gear engaged and taking the boot off the throttle. Being in control of the car means having 2 hands on the wheel as much as possible in my opinion but whatever you are comfortable with. Regarding clutch wear as a rule of thumb, if its smooth its not wearing if its jerky it is!

DaMonk

Mr.David wrote: »

Its somewhat down to personal preference. I often brake down from 5th to 3rd for instance. Coasting should definitely be avoided and it actually uses more fuel than leaving the gear engaged and taking the boot off the throttle. Being in control of the car means having 2 hands on the wheel as much as possible in my opinion but whatever you are comfortable with. Regarding clutch wear as a rule of thumb, if its smooth its not wearing if its jerky it is!

Is this true because I thought by pressing the go accelerator before the clutch is released is slipping and thats smoother than waiting to take your foot off the clutch fully?

mickdw

esel wrote: »

It's not for when you are slowing down, it's for when you know you are coming to a stop.

Thats still no way to be driving. You are always more in control of the car with some power available. Fair enough you are intending to stop but if you do this down through all the gears from speed, it is possible that on occasion you may have to take evasive action of some kind before you stop the car and then you need the car to be responsive. Also if you do this when coming to a stop it will become habit and you would probably start to drive continuously in that manner thus ruining your driving style. I would challenge any instructer (advanced or not) who recommended that.

ianobrien

mickdw wrote: »

Thats still no way to be driving. You are always more in control of the car with some power available. Fair enough you are intending to stop but if you do this down through all the gears from speed, it is possible that on occasion you may have to take evasive action of some kind before you stop the car and then you need the car to be responsive. Also if you do this when coming to a stop it will become habit and you would probably start to drive continuously in that manner thus ruining your driving style. I would challenge any instructer (advanced or not) who recommended that.

I'd agree with that. Having some power available is handy for when the back steps out on a greasy road:D

(Yes, before I get shot here about speeding, poor driving, etc, I do like driving, and regularly have the back of a 05 Almera out sideways and not from the handbrake. I blame the wet roads and crap tyres, rather than the speed! And yes, it's only on quiet roads and private lanes I do it, not the main road)

peasant

ianobrien wrote: »

I'd agree with that. Having some power available is handy for when the back steps out on a greasy road:D

(Yes, before I get shot here about speeding, poor driving, etc, I do like driving, and regularly have the back of a 05 Almera out sideways and not from the handbrake. I blame the wet roads and crap tyres, rather than the speed! And yes, it's only on quiet roads and private lanes I do it, not the main road)

two things wrong with this post

a) last time I checked the almera was FWD

b) it's miles off topic

Zube

mickdw wrote: »

You are always more in control of the car with some power available.

That's the conventional wisdom the Irish testers are looking for.

Does the same logic apply when cruising along? Do you hang on to 3rd at 60 in case you need a burst of power? No, you drive in the lowest appropriate gear. Whipping through all five or six gears on the way down to a stop is just a pointless ingrained habit.

Honey-ec

Intersting article on engine vs hydraulic breaking here: http://www.straightdope.com/classics/a980227.html

Eddie Cunningham also addressed it in his column in the Indo a few years back - his advice was "Gears to go, brakes to slow" - snappy, eh?

Esel

Mr.David wrote: »

Being in control of the car means having 2 hands on the wheel as much as possible....

Ergo, automatic gearbox!

echo hotel

Mr.David wrote: »

Regarding Rev matching, the easiest way to try it is not to let the accel out when downchanging. i.e. travelling at 35mph in 4th, with your foot on the accelerator (not gaining momentum just staying constant) clutch in and change gear swiftly (keeping foot on throttle the whole time). This has the effect of blipping the revs to match the required revs for the lower gear. Its much smoother once you get the hang of it.

Once you have mastered that you can try powershifting i.e. changing gear without clutching at all, it only requires you to match revs carefully. Its faster (was employed by rally drivers for instance) and does not damage the car as long as done well.

ruins the syncronising rings in the box if you screw up though then you'll never get gear

ianobrien

peasant wrote: »

two things wrong with this post

a) last time I checked the almera was FWD

b) it's miles off topic

1. lift off oversteer and left foot braking will put an almera sideways in the wet 2. The advantage of having some power left in the was mentioned for control. I also said power was handy for controlling slides 3. If you want to see an almera sideways, pm me and we'll meet up and I'll show you how it's done

echo hotel

DaMonk wrote: »

I know that ya. Just wondering if I'm wearing my clutch needlessly by engine breaking when I could just be breaking normally. Engine breaking is a habit by now and I hate coasting but since my clutch is going to get worn more due to remapping I'm trying to keep all other wear at a minimum.

On a side note, is it better or worse for the clutch to come off it faster when accelerating gears? From 1st for instance?

the less your foot is on the pedal the less you're goin to wear the clutch also when not using the clutch make sure your foot isn't resting on the pedal as there is a few millimeters of play to protect the release bearing any preasure on the pedal will cause this to wear quicker