Originally posted by sigma:
How does downshifting burn more fuel? Just because revs go up doesn't mean you're burning more gas -- there's load on the engine from the wheels that's making it rev, not combustion of fuel.



Huh ? Fuel is burnt accordingly to how many rpm. That's why you'll have worse gas mileage if you try to drive in too high a gear at too low a speed.

Anyway, re: double clutching, here's a good explanation:

Quote:


When you double clutch on the downshift you are revmatching, but that does not mean that revmatching is double clutching.


Revmatching

1. Clutch in
2. Blip Throttle
4. Downshift
3. Clutch out

This is the most common (n00b) way of revmatching on the downshift. Your synchros still have to accellerate the layshaft to the speed of the output shaft, hence synchro wear is no different than just waiting for RPMs to drop and then downshifting. Essentially you are accellerating the rotating speed of the engine so that when you engage the clutch they will be moving the same speed. It is slower than double clutching, but less advanced and will let you get used to blipping the throttle while braking. Done correctly this method eliminated brake bias due to engine braking and reduces clutch wear since you are at no time dragging it.

Double Clutch Revmatching

1. Clutch in
2. Shift to Neutral
3. Clutch out
4. Blip Throttle
5. Clutch in
6. Downshift
7. Clutch out

This method allows for a much faster downshift as you do not have to rely on the synchromeshes to accellerate the layshaft to the speed of the output shaft. The lever literally falls into place with a feather's touch as layshaft and output shaft are perfectly matched. Virtually no synchro or clutch wear, and your downshift will be nearly instantanious once you get used to dancing all over your pedals.

Read my earlier post for a better description of Double Clutching.