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Rona_Drifter
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Location:
Sunny Coast
Registered:
March 2005

Re: Double clutching?

Sun, 14 August 2005 11:12

white86 wrote on Sun, 14 August 2005 15:20

ok boys and girls... let's get this straight

Flat shifting is changing up gears without touching the CLUTCH. To do this you very often have to momentarily lift the throttle a slight amount. This can be seen in V8 Supercars for instance, where the Motec computer actually cuts the ignition for a split second during an upchange, so that the driver can leave his foot flat on the throttle too.

Double clutching in a synchro car is pointless on upchanges! You actually want the revs to drop slightly to match the next higher gear, hence lifting the throttle.

Downshifts are a different story however. The heel-and-toe technique is used to blip the throttle to raise revs to match the next lower gear. This is done in racing/quick driving situations so that when the clutch is released you don't experience a small amount of compression lock (ie. cruise along at 40km/h in 3rd, change down to second and side-step off the clutch - the back wheels will chirp).

However, can I just make the definition between double-clutching and heel-and-toeing clear? Both of these practices refer to changing DOWN gears, ie 4th to 3rd.

DOUBLE CLUTCH - Driving in 4th gear. Throttle completely lifted. Clutch in. Shift to neutral. Clutch out. Blip the throttle. Clutch in. Shift to 3rd. Clutch out.

HEEL AND TOE - Driving in 4th gear. Right foot presses the brake peddle with toes. Clutch in. Shift through neutral directly to third gear while rotating the right foot and tapping the throttle with the heel/side. Then immediately lift the left foot of the clutch. This whole process is sort of a fluid motion. Can also be done without the braking, ie to shift down to go up a hill.

Both of these techniques aim to ease the box into gear and reduce driveline stresses/associated compression lock by matching engine revs to the lower gear. By this I mean that driving at 60km/h in 4th gear, engine revs might be at 2500 rpm. However, at 60km/h in 3rd gear, the engine might be pulling 3500rpm. Therefore the blipping of the throttle in both techniques aims to raise engine revs by this amount (as loss in road speed is negligable). Doing so stops the engine from being forced to speed up while the clutch is being released. In a racing situation, heel-and-toeing allows very quick downshifts, and you don't have to worry about slowly letting the clutch out to avoid lock

Ah yes, finally someone who knows what they're talking about. The only times anyone should ever double clutch is:
1. When ya syncro's r rooted
2. Your driving a truck with a dog box
and even then its only realy when changing DOWN because that puts the most load on ya mesh.

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