Quote:
Originally Posted by GTR34
Hmm, I see. Well the shifting method seems to make sense, but is double clutching required or could I just rev match?
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They are two complimentary entities. Since I'm never sure just what people know and don't know, I'll explain. Rev matching is basically what it sounds like and is done after you actually get into the new gear you are shifting to. Once you have already shifted to the new gear, you either wait for the engine to slow down to the correct rpm it would need to be for the next gear before letting the clutch out in an upshift, or blipping the throttle to raise the revs to near the required amount for the next gear before letting the clutch out in a downshift. You are taking that extra second to make your clutch last a lot longer by working the throttle to put the engine where it needs to be for the new gear rather than just making the clutch force the engine to the speed it needs to be in. It becomes more important for clutch life the higher the rpm range you are working at, as let's say hypothetically you are in 3rd at 1500 rpm and you want to downshift to 2nd. The engine will only have to speed up to maybe 2200 rpm to match the shift. Not too terrible to ask the clutch to do that. If you are in 3rd at 3000 and want to downshift into 2nd, the engine will have to be something like 5000 rpm...a lot more work for the clutch! Just use the throttle to kick the engine up to around 5000 rpm while the clutch is in and you are shifting into 2nd, so that when you release the clutch, the engine is already at the rpm it needs to be. You will actually have to overshoot the rpm mark a little to allow for any latencies involved in your execution, plus I find it easier to overshoot the mark and just catch the matched rev as the engine slows down rather than try to shoot up to the mark exactly or even catch the mark on the way up the rpm. Your clutch will thank you.
Double clutching is how you actually get into the new gear without beating on the synchros (or if the synchros are shot, or the gearbox is non-synchronized). It is only required for downshifting. So say you are rolling along in 4th gear at 2000 rpm and someone is sucking at life driving 10 under the limit in front of you and you need to pass. In order to be in 2nd at the current road speed, let's say the engine needs to be at 4500 rpm. So think about what needs to happen in order to not work the synchros... the transmission input shaft has to be somehow sped up to around 4500 rpm before 2nd can engage. Without this technique, the synchros are the ones doing that work and it is a lot of work on these cars as mentioned before. What you do is let off the gas and put the clutch in just like for a regular shift, drop the stick into neutral, kick the engine revs up to around the target rpm while releasing the clutch again to speed up the driveshaft/input shaft, push the clutch right back in and push the stick into 2nd (or whatever gear you're shifting to), and then rev match to engage the clutch in the new gear. The part you do in neutral happens very fast once you get the hang of it. You are basically kicking the revs up while letting the clutch out and then right back in, making the timing such that the clutch is engaged at the same split second the revs are near the target, and then shifting immediately after the you push the clutch in so as to not allow the driveshaft to slow down again. When everything is timed correctly, the stick will go into the lower gear with minimum effort. Once you learn the gear spacings and practice the technique, it is nearly as fast as a regular downshift. It's much easier to show than to explain.
Now you can also help the synchros in upshifting by just applying light pressure to the stick once you push the clutch in and let the revs drop, and once the input shaft speed matches, the stick will just drop into gear. That's the same shifting feeling you want in a properly executed double clutch downshift.