Rev Matching & the mistakes made

[cmaguire]

I don't put any more significant strain on the clutch during down-shifting than it gets from a brisk pull-away, and the wear is to the friction material only as opposed to the less desirable strain put on gearbox/clutch if dumping it. And this only happens if slowing from speed anyway, when the clutch is in a queue of items up for wear-and-tear whatever you do. When the vehicle goes to meet its maker, having a pristine clutch isn't likely to give me much satisfaction either, although the mileage I get out of my clutches is perhaps higher than might be expected given the speeds the vehicles do.

[dvenman]

cmaguire said:

the wear is to the friction material only as opposed to the less desirable strain put on gearbox/clutch

The point of rev matching being to reduce wear on the friction surfaces as well while changing, and getting a really consistent gear change quality.

[cmaguire]

dvenman said:

The point of rev matching being to reduce wear on the friction surfaces as well while changing, and getting a really consistent gear change quality.

Is that the only point then? Why bother, it won't speed you up (and may slow the whole process down) and a synchromesh gearbox isn't a sequential straight box.

[waremark]

cmaguire said:

Is that the only point then? Why bother, it won't speed you up (and may slow the whole process down) and a synchromesh gearbox isn't a sequential straight box.

No, it is also worth doing for the satisfaction. It is extremely satisfying every time the clutch comes up with no change in revs and no physical sensation. If that's not something you enjoy, why wouldn't you choose a paddle shift car?

[Dr Jekyll]

waremark said:

cmaguire said:

Is that the only point then? Why bother, it won't speed you up (and may slow the whole process down) and a synchromesh gearbox isn't a sequential straight box.

No, it is also worth doing for the satisfaction. It is extremely satisfying every time the clutch comes up with no change in revs and no physical sensation. If that's not something you enjoy, why wouldn't you choose a paddle shift car?

It's also more comfortable for the passengers.

[akirk]

Dr Jekyll said:

waremark said:

cmaguire said:

Is that the only point then? Why bother, it won't speed you up (and may slow the whole process down) and a synchromesh gearbox isn't a sequential straight box.

No, it is also worth doing for the satisfaction. It is extremely satisfying every time the clutch comes up with no change in revs and no physical sensation. If that's not something you enjoy, why wouldn't you choose a paddle shift car?

It's also more comfortable for the passengers.

def. this - and of course it can depend on the car - the M5 has a very light flywheel, so, not rev matching leads to a jolt through the drivetrain / car which is very disturbing - in other cars, like the octavia scout I had previously, far less noticeable...

[Young1]

Thanks for all your help! Just a quick clarification here: Am I doing anything bad by changing down and then whilst foot is on clutch squeezing the accelerator WHILST lifting the clutch? No surprise that it speeds off a little bit initially (over revving it slightly i reckon) but other than that the change itself feels smooth.

[dvenman]

Young1 said:

Thanks for all your help! Just a quick clarification here: Am I doing anything bad by changing down and then whilst foot is on clutch squeezing the accelerator WHILST lifting the clutch? No surprise that it speeds off a little bit initially (over revving it slightly i reckon) but other than that the change itself feels smooth.

I wouldn't say so, and you can refine it over time by getting the engine and road RPM matched as close as possible - but if you extend the aim of the game to be that your passengers couldn't detect a gear change except by the fact your hand moves and there's a small RPM increase then you may find that also goes away.

[IcedKiwi]

One thing I also found helped was trying to make sure my foot was on the accelerator before pushing in the clutch. The revs won't fall as soon as you push in the clutch now and you therefore have less revs to make up, use a smaller throttle input and maybe not overshoot as much.

[dvenman]

IcedKiwi said:

make sure my foot was on the accelerator before pushing in the clutch

Forgot to say, and IK has reminded me - if you keep your foot still on the gas pedal during the gear change, and make the gear lever movement a 1 - 2 count then bring the clutch up, the revs will rise to pretty much where they need to be. If you rush the process you'll need to move the right foot a little.

[Young1]

Awesome thanks for that!

[mph999]

dvenman said:

Forgot to say, and IK has reminded me - if you keep your foot still on the gas pedal during the gear change, and make the gear lever movement a 1 - 2 count then bring the clutch up, the revs will rise to pretty much where they need to be. If you rush the process you'll need to move the right foot a little.

Only works on the flat, try that going uphill and you'll bounce of the limiter ...

It is however, a good way of getting a rough idea of how it works.

[dvenman]

mph999 said:

try that going uphill and you'll bounce of the limiter ...

Never experienced that, my car doesn't know it's going uphill or not and if the gear change is complete before there's an appreciable deceleration I've always found it works the same.

Downhill - slightly different matter as the car will tend to accelerate and you need to cater for that.

[waremark]

dvenman said:

mph999 said:

try that going uphill and you'll bounce of the limiter ...

Never experienced that, my car doesn't know it's going uphill or not and if the gear change is complete before there's an appreciable deceleration I've always found it works the same.

Downhill - slightly different matter as the car will tend to accelerate and you need to cater for that.

I'm with mph999 on this. If you don't have to have your foot further down when going uphill I would like to know what you are driving. Actually, I think even on the flat you have to lift your right foot a little if you don't want the revs to flare too high, and the lift is greater uphill.

[dvenman]

waremark said:

I'm with mph999 on this. If you don't have to have your foot further down when going uphill I would like to know what you are driving. Actually, I think even on the flat you have to lift your right foot a little if you don't want the revs to flare too high, and the lift is greater uphill.

I'll have to give it a try - but I'm currently not driving because of a shoulder operation. Stuck with public transport...and boy, some bus drivers could really do with lessons in smoothness.

[mph999]

waremark said:

dvenman said:

mph999 said:

try that going uphill and you'll bounce of the limiter ...

Never experienced that, my car doesn't know it's going uphill or not and if the gear change is complete before there's an appreciable deceleration I've always found it works the same.

Downhill - slightly different matter as the car will tend to accelerate and you need to cater for that.

I'm with mph999 on this. If you don't have to have your foot further down when going uphill I would like to know what you are driving. Actually, I think even on the flat you have to lift your right foot a little if you don't want the revs to flare too high, and the lift is greater uphill.

Depends what you are driving - it's not a method I like personally as it is too hit and miss.

As the gears are ratios, the amount of blip you need between say 4th and 3rd differs at different speeds :

For example (I'm making these numbers up to make it easy)

If the ratio between 3rd and 4th is 2:1

Speed revs 4th revs 3rd
60mph 3000 6000
30mph 1500 3000

The difference in revs between 4th and 3rd at 60mph is 3000, whereas at 30mph it is only 1500.
OK, these numbers are totally made up just to make it easy to see - but for the same two gears, the amount of 'blip' you need changes depending on the speed you are doing. I've found that for a given pair of gears it works well at some road speeds, and not others.

[Pica-Pica]

I can double declitch, but as others have said, modern cars (my 19 year old E36) can handle this quite well with regards to clutch and synchro wear quite well over their lifetime.

I have a ZF8 Auto now, but in my last years with the manual I loved to practice completely clutchless gear changes. Then you have to rev-match pretty well to, (a) enable a load free move OUT of gear, and (b) avoid the synchro baulking the move INTO the next gear.