car talk says double clutching is bad?

[daniel]

i've been double clutching for a few years now... then i hear that it is actually bad for the car to do so from the car talk guys. here i thought i was saving the clutch from unnecessary wear. i figured downshifting (say from 3rd to 2nd) then letting the clutch out to get that lurch feeling was just extra, unneeded wear on the clutch.

discuss.

[gtdragon980]

i never really understood the point in double clutching....and doesn't rev-matching eliminate that lurch when downshifting?

[meidlin]

Double Clutch:

Masturbating with one hand while intentionally cutting off oxygen to the brain with the other hand for the purpose of sexual gratification. See also Auto Erotic Asphyxiation.

... Wait, What?

[nando]

learn how to rev match, you don't drive a 1960s pickup with no synchros in the transmission.

[Hick]

helps with worn out syncros

[BenM]

What?

Double clutching doesn't have anything to do with prematurely wearing the clutch. It is a technique used when driving older cars that do not have synchros (say a 1948 Ford F5). Double clutching on a newer car with perfectly good synchros is silly.

edit- nando beat me to it. :P

[TDE30]

learn how to rev match

This.

[daniel]

i never really understood the point in double clutching....and doesn't rev-matching eliminate that lurch when downshifting?

revmatching eliminates the lurch but puts wear on the synchros. there is something extremely satisfying about doubleclutching and effortlessly slipping into a lower gear with no resistance.

i don't think ill ever stop doubleclutching since it is just naturally what i do now, but i wanted to hear what others thought about the idea. the car talk guys specifically said it wears out the clutch faster, which doesn't make sense to me.

[nando]

Well there's no harm in doing it, but as far as saving the synchros, I'm not sure it's needed unless they are already bad. I have 260k on my getrag 260 and all the synchros are fine, I know there are lots of others who could say the same.

I think knowing both methods would be beneficial. If you ever do any HPDEs, you'll want to know how to rev match. Just last week I was watching a video of an E30 with a seriously built engine, but the driver was just letting out the clutch to downshift and nearly spinning out on ever corner entry.. yikes!

[Wh33lhop]

revmatching eliminates the lurch but puts wear on the synchros. there is something extremely satisfying about doubleclutching and effortlessly slipping into a lower gear with no resistance.

i don't think ill ever stop doubleclutching since it is just naturally what i do now, but i wanted to hear what others thought about the idea. the car talk guys specifically said it wears out the clutch faster, which doesn't make sense to me.

I do it too, effortless downshifts are very satisfying. I've found, though, that it's easier to rev match smoother lurch-wise than it is to double-clutch, just because the object of a double clutch is to match the revs in neutral (then perform the second clutch, clutch in, complete the shift, clutch out--more time for revs to drop) whereas in rev-matching you tend to have the revs matched right as you're releasing the clutch.

It's also nice to be able to double-clutch into first, just to be a jackass coming to stoplights :p

[Hallen]

I would suspect you are doing putting more wear in both the throw out bearing and the clutch by double clutching. In double clutching, you are engaging the clutch twice during each shift. The clutch and the flywheel will be spinning at different rates and every time the clutch squishes up against the flywheel, you are going to get wear.

Rev matching is the ticket. If you minimize the speed difference between the clutch and the flywheel and you minimize the length of time the clutch spends spinning against the flywheel, the less wear you are going to have. Think about it: you burn a clutch up by trying to feather the clutch while accelerating. You get more wear by doing that than you do if you rapidly engage the clutch causing a bit of a jerk (which can be eliminated with good rev matching). But the clutch spins less so you are doing as much to it. Anyway, that's just my take on it.

[Wh33lhop]

I think knowing both methods would be beneficial. If you ever do any HPDEs, you'll want to know how to rev match. Just last week I was watching a video of an E30 with a seriously built engine, but the driver was just letting out the clutch to downshift and nearly spinning out on ever corner entry.. yikes!

The phrase you are looking for is heel-toe :p

There's a video of an engineer test driving the E92 M3 around some track chirping the tires on every downshift. I cringed.

Or there's this tool:



Fucking ugliest S38 swapped E30 on the planet whose owners abuses a slipping clutch and can't even heel-toe.

[nando]

The phrase you are looking for is heel-toe :p

that's the common name for it, but since I don't actually use my heel, rev matching is a better term. It's more like pinky toe/ball of foot. ;)

[delfin]

Can someone explain exactly what double clutching is?

[daniel]

Can someone explain exactly what double clutching is?

car in 3rd gear, 3000 RPM. push clutch in, shift into neutral. release clutch, which matches the transmission speed with the engine speed. rev up to 4000RPM, push clutch in, and smoothly, creamily slip the shift lever into 2nd gear, then let the clutch out.

its all about knowing the RPMs in each gear for a given speed so you can shift between gears and adjust the RPMs accordingly.

btw if you ever want to drive without the clutch, you do a similar thing, except you don't use the clutch.