Merou

ok so after reading the article on Driver's Edge on downshift I understand how it's done (don't get me wrong, I still can't do it), but I'm still not sure I understand *why* it's done... First: you only double clutch when downshifting, right? And when you're downshifting not to slow down, but to have more pick-up, right? Now what I understand that the point is to bring the rpm up to match the wheels' revs, but why double-clutch? Can't you up the throttle when the clutch is down the first time? Or does it not really matter on cars with modern sychronizers? Speaking of - are synchronizers a mechanic or electronic piece of equipment? How does it wear?
Lots of questions huh? =)

Rennen

....did the rev-matching for you. Double-clutching is not necessary but many people do it anyway. Many do it because they have learned to do it that way and like to drive that way. I think it really still helps in racing, however, to smoothly transition between gears w/o knocking off speed when approaching a turn.

evan

regardless of rpms... useful in all sorts of everyday driving, and I DC on most downshifts. Of course, it is particularly splendid for 6th-to-4th or 6th-to-3rd downshifts when you need some serious acceleration. :-)

smallTTs

Double-clutching ususally is only when down shifting, unless it's an non-synchronized gerbox.

You are attempting to get the gears in the trans. spinning at the correct rpm to match driveshaft speed. By shifting into neutral (first clutching) then enganing the clutch, the engine can then speed up the gears when you blip it. The second clutching then disengages the engine from all those spinning gears, which are slowing down rapidly(!), so you can select lower gear, and re-engage the clutch.

Synchros are mechanical bits on the transmission shafts which when they touch just before gears mesh, smoothly mate the two gears so the one not under drive loads speeds up (downshifting) or slows down (upshifting) to the same rpm as the one under load so gear teeth mesh smoothly. This negates the requirement to double clutch.

These synchros do a great job, and unless the driver is very precise, double-clutching doesn't do much, if any good. It could even make the synchros work harder.

Just blipping the engine when clutch is disengaged during a (single-clutching) downshift just makes the clutch engagement smoother, not the gear engagement.

IMO, fun to practice, but not really very useful. Others will have the opposite opinion.

My $.02

Rennen

I agree and do it quite often myself.

Merou

very helpful, thanks!