car talk says double clutching is bad?

[Beach Bum]

i think i fucked shit up in my passat from clutchless shifting too much

Synchros. They're not made to mitigate that kind of force.

[Tbolt]

i think i fucked shit up in my passat from clutchless shifting too much

[wolfgangstbd]

:giggle:i was double cluching today jsut because of this thread

[87e30]

Fair enough. You're a quick double clutcher. ;)

You're left calf must be huge!

I'll stick to my good 'ol rev matching.

[Wh33lhop]

Video sucks.

[Danny]

Video sucks.

[Wh33lhop]

Went out for a quick drive to make sure I wasn't smoking crack. It's pretty close.

[nando]

it probably is, but I'll stick to heel/toe for track driving. :p

actually been trying DCing a little bit, there's a railroad crossing I like to slow down for. I can DC down into 4th and 3rd pretty smooth, but since I have to hit the brakes to slow down enough for the crossing (20mph in 2nd) I heel/toe for 2nd.

[Wh33lhop]

I'd like to ride with your DCing that's as fast as rev matching.

Rev matching = push clutch, tap gas, move shift, release clutch

DCing = push clutch, move shift, release clutch, tap gas, push clutch, move shift, release clutch.

Unless I'm missing something DCing is not as fast...

When you get good at it, it's all one fluid motion and it's pretty quick.

[87e30]

thanks :)

the smoothness comes in the form of the actual gear lever sliding into a lower gear easily with no reaction from the car in any way. I don't like that ounce more of effort required to use the synchros to get into gear, so i double clutch. it doesn't take much longer to do than basic rev-matching, you just have to do a little dance with your left foot.

no problemo.

I'd like to ride with your DCing that's as fast as rev matching.

Rev matching = push clutch, tap gas, move shift, release clutch

DCing = push clutch, move shift, release clutch, tap gas, push clutch, move shift, release clutch.

Unless I'm missing something DCing is not as fast...

[Wh33lhop]

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.

The only extra wear you are putting on the clutch is when you're using the clutch to spin the input shaft. I'm not exactly sure what the moment of inertia the input shaft has, but suffice it to say it's under 1% of the comparable equivalent moment of inertia the entire car would have in first gear. You are saying a clutch that's designed to start a 3000lb car from a rest hundreds of thousands of times before it wears out is going to be worn by a 15lb 12" disc and a 5lb 1" diameter input shaft? Get real. That is beyond negligible, I don't care how much more you have to rotationally accelerate the input shaft than the car.

And as for the throwout bearing, that is worn more based on how long and to what extent the clutch is depressed, not on how many times. Think about it.

You want to state that double clutching is unnecessary since synchros will last forever? Fine, not only are we on the same page, but I agree with you. But what you are posting is immaterial.

[z31maniac]

my zf320 has 95k miles on it, and the clutch has about 15k miles on it w/ a lightweight flywheel.

I was talking about mine.

[txtorquemade]

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.

Kinda think I agree with that. From a purely physics standpoint, it makes sense. :);)

[Wh33lhop]

there isn't much point in downshifting past 2nd really. You get overrun fuel cut down to ~1500rpm with the stock computer, which is slow enough in 2nd gear that you're almost stopped anyway.

the only time I ever needed 1st for a corner was an extremely tight autox, which was very rare. I hated doing it too, although it surprised me a bit when it just slipped right into gear. Otherwise, yah, you're just beating up on your car for no good reason..

To each his own. Not all of us have high compression 2.8 strokers that put out any torque below 3500rpm though. :p

[nando]

First gear turns, downshifting for a stop light and thinking you're awesome, etc.

there isn't much point in downshifting past 2nd really. You get overrun fuel cut down to ~1500rpm with the stock computer, which is slow enough in 2nd gear that you're almost stopped anyway.

the only time I ever needed 1st for a corner was an extremely tight autox, which was very rare. I hated doing it too, although it surprised me a bit when it just slipped right into gear. Otherwise, yah, you're just beating up on your car for no good reason..