[benton0311]

I picked up the habit of double clutching a little over a decade ago when I had a WRX with crappy synchros. I used to rev match before that but I've been double clutching my downshifts for so long that I do it subconsciously and I have have a hard time going back to just rev matching.

My question is: does double clutching accelerate clutch wear appreciably since the clutch is engaged twice or is it mitigated by the smooth/low-load engagement of the clutch with each engagement? I understand that double clutching is completely unnecessary on a car with healthy synchros but I'm wondering if it can be detrimental to clutch life.

I found an old thread related to the topic but it addressed more how to double clutch with heel and toe and the relevance of the technique.

[HouseN54]

Race Wars?

[The HACK]

Double clutching wears on the throw-out bearings but saves the synchros. Replacing the throw-out bearing is almost STANDARD on replacing the clutch, and if your t.o. bearing should ever fail before the clutch, replacing it cost around $500 in labor. Replacing the synchros? Cost you a metric sh*t ton more (in fact, it would be cheaper to buy a re-built transmission).

Rev matching is far more important to extend the life of the drive-train though. To do it and do it right, you should double clutch AND rev match. However, neither the synchros nor the t.o. bearing is a common wear and tear item, the synchros should last the life of your car and the t.o. bearing is basically replaced every time the clutch is replaced...Makes double clutching to save the synchros moot. I had an E30 318is with 350,000+ miles on the original transmission and a 2nd set of clutch when I let it go, and I'm sure the previous owner never bothered to double clutch and neither did I...The synchro seems fine and the t.o. bearing never failed before the clutch replacement.

The only problem with double clutching for track use, is that if you're not familiar with it and can basically do it in a split second, you'll be de-coupling the drivetrain needlessly long, and the idea for track use is your drive train should be connected for as long as you can/want.

[benton0311]

The second clutch out is rev matched so there would be smooth engagement there. It makes sense that the throw out bearing would wear faster but I wouldn't think it would fail before the disc was due to be replaced (either the disc would be worn out or close enough that it would be time for a new clutch anyway).

I guess the real question is whether the double clutch engagement causes double the wear to the disc or if the extra engagement doesn't cause appreciable wear since the transmission is in neutral and isn't under much load.

If it causes double the wear to the disc, then it would be something that I'll need to make a conscious effort to stop doing which will take some effort since I've been doing it for so long.

[CJ421]

I double clutch downshift as well (except heel-toe on track - I only rev-match) and it would be news to me if doing so produced excess wear. You might ask the gearheads over at StandardShift.com forums or search around there a bit. In my time there, I didn't read about any downsides to double clutching on modern transmissions. Modern synchros have supposedly eliminated the benefit of double clutching vs. rev-match only but - the synchros are definitely used less in a double clutch downshift; you can tell by how easily the gears engage vs. simply rev matching.

[LaserPower]

I just don't see the need for double clutching at all. When downshifting, under braking you can just heel and toe (E90 gas and brake pedals are so well positioned there should not be any difficulty to heel and toe even under very light braking). When not under braking you can just blip the throttle to bring up the RPM at the same time as gear change to rev match. Pressing and releasing clutch twice is just a waste of time. Unless you want to shift really slowly. But why would you shift really slowly...?

[chris82]

Originally Posted by CJ421

I double clutch downshift as well (except heel-toe on track - I only rev-match) and it would be news to me if doing so produced excess wear. You might ask the gearheads over at StandardShift.com forums or search around there a bit. In my time there, I didn't read about any downsides to double clutching on modern transmissions. Modern synchros have supposedly eliminated the benefit of double clutching vs. rev-match only but - the synchros are definitely used less in a double clutch downshift; you can tell by how easily the gears engage vs. simply rev matching.

I bet it's easy to do with that rev-hanging turbo'd engine too

[CJ421]

Originally Posted by chris82

I bet it's easy to do with that rev-hanging turbo'd engine too

Don't even get me started on rev-hang with this car ...