Hey C4S,
Firstly, in my opinion the guys from F&F were talking crap... (or maybe there is a reason i am completely unaware of?)
Nowadays cars have syncromesh's on all forward gears, so this makes it pointless to double clutch. Let me try and explain why -
Let me just say once again i am going to simplfy all the processes so the concept can be clearly understood.
Lets say we have 4 main rotating parts
1 - Clutch
2 - Input axle to gear box (between clutch and gearbox)
3 - Output axle from gearbox
4 - the actual gear selector cog(s) (this is the simplified part). When u select a gear all you are doing is moving this "part" around, allowing it to make contact with different gears of different sizes, hence giving different gear ratios.
This is a diagram (just try and realize that the opening on the TOP where the gearlever is connected is connected to a lever in the gearbox that moves around the "moving part"
Lets do a hypothetical upshift from 1st to 2nd without doubleclutching (in a car with a syncromeshed gearbox -ie any car in the last 10++ years)
You are in 1st gear, the engine is at 5,000Rpm, you press the clutch and almost simultaneously release the accelerator.
Shift the gearstick into Neutral, and then continue to push it into second. (where the engine will only be revving at 2,500Rpm)
(Now the part that u are shifting in the gearbox was spinning really fast when u were in first and is still freewheeling very fast in neutral, so when u are pushing into 2nd this is where a syncro comes in....it is like a mini-clutch or think of it as a "Cushion" on the gear that basically gets the moveable peice spinning at the same speed so that when you push into 2nd gear it slides in without any problem.
Hope that was clear!
If you got that it should be quite simple to understand double clutching now - (remember u want to double clutch when there are no syncros)
ok, so you are doing the same 1st to 2nd upshift using dblcltching..
You are in 1st gear, the engine is at 5,000Rpm, you press the clutch and almost simultaneously release the accelerator.
Shift the gearstick into Neutral, and THEN RELEASE THE CLUTCH (this completes 1 "clutching").
By releasing the clutch and having stepped off the accelerator, now the engine is spinning at 2,500rpm which is similar to what is will be revving at in 2nd gear at this speed (u are controlling engine revs). Since the clutch is not pressed and the car is in neutral the "moveable peice" spins at a speed relative to that of the engine.
then PRESS THE CLUTCH AGAIN (2nd clutching) and continue to push it into second. (where the engine will only be revving at 2,500Rpm, which is the speed that the "moveable peice" is aldready spinning at!
Thats basically the basics of it!
As you can now see...double clutching in modern cars is just a waste of time (i cant think of a reason to.....) except sometimes when u are going a bit fast in 2nd and u try and put the car in 1st and it doesnt slot in (i assume u guys know what i am talking abt?) then u just leave it in neutral..leave the clutch...revv the engine...press the clutch and it slots straight into 1st!..there...you just double clutched. I guess in this scenario the syncros were just having a hard time bringing the "moving peice" up to speed??
Im sorry i didnt explain the way the gearbox works in any detail..but it is complicated...so find a good site with pics and.wait...here..this seems to be a great one.....
Howstuffworks "How Manual Transmissions Work"
check out the whole site...you will learn a lot...and they have some awesomely helpful flash animations to explain things.
Gearbox's are truly amazing peices of engineering! just try in your mind to create one...even if you aldready know how they work and its still incredibly tough!
cheers.....
Rehaan.