At what point are the shifting synchros actually engaged? Is it when you actually shift or when you release the clutch?

If it is when you release the clutch, than does it matter if one depresses the clutch, shifts, rev match, release the clutch vs. clutch, rev match, shift, release?

Furthermore, how would this compare to downshifting to 2nd at 50 mph and just slowly releasing the clutch to allow everything to slowing rev up to speed? (I know this is a slow technique and not appropriate for racing)

Isn't the purpose of rev matching to improve the "smoothness" of your shifting and reduce wear on the synchros? or have I had one too many hurricaines

 

The synchros work when you are moving the shfter from one gear to the next. Their job is bring the shaft speed up to where it needs to be for the gears to engage each other.

By rev matching, you bring the speed of the shaft up to where it will be when the gears engage. The way you do this is by double clutching. If you are good at this, you can eliminate or reduce the wear on the synchros.

You can also "rev match" by blipping the thottle while downshifting so that the engine is at the same speed when you release the clutch. This still uses the synchros, unless you double clutch, but make the braking/turning/acceleration our of a turn much smoother and quicker.

A good driver who can do double clutching well will have much less wear on his transmission than the person who shifts and slowly lets out his clutch. The latter will will wear a clutch out faster, while the former will reduce wear on the clutch disk as well as the synchros.

Look at this link: http://www.howstuffworks.com/transmission4.htm

 

thanks