Question about car Backlash
09-01-2005, 05:30 AM
#21
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When it comes to synchros and rev matching, the thing to keep in mind is that there are really 3 sections of the driveline that can turn at different speeds, not 2.
First you have the engine, it will spin at a certain speed.
Second, you have the clutch and input shaft into the tranny.
Third, you have the output shaft of the tranny which goes to the differential and wheels.
It's the second part that comes in to real play here.
Ok, double clutch rev-matching:
Engine is spinning at 5k rpm, you clutch in --- section 1 drops RPMs, sections 2 and 3 still linked and spinning at same speed.
You shift into neutral and clutch out --- section one continues to shave off RPMs, section 2 spins down to section 1's speed. Section 3 continues loosing only as much speed as the car does since it's attached to the wheels.
You rev the engine -- Sections 1 and 2 gain RPMs. Here you're attempting to match speed between sections 1/2 and section 3 given the new gearing ratio.
You clutch in and switch to next gear --- At this point, if you rev-matched correctly, the section 2's RPMs will match section 3's RPMs (as adjusted for the gear ratio) and the synchros will get minimal use.
You clutch out and continue accellerating --- The clutch did most of the work, thus preserving your synchros.
First you have the engine, it will spin at a certain speed.
Second, you have the clutch and input shaft into the tranny.
Third, you have the output shaft of the tranny which goes to the differential and wheels.
It's the second part that comes in to real play here.
Ok, double clutch rev-matching:
Engine is spinning at 5k rpm, you clutch in --- section 1 drops RPMs, sections 2 and 3 still linked and spinning at same speed.
You shift into neutral and clutch out --- section one continues to shave off RPMs, section 2 spins down to section 1's speed. Section 3 continues loosing only as much speed as the car does since it's attached to the wheels.
You rev the engine -- Sections 1 and 2 gain RPMs. Here you're attempting to match speed between sections 1/2 and section 3 given the new gearing ratio.
You clutch in and switch to next gear --- At this point, if you rev-matched correctly, the section 2's RPMs will match section 3's RPMs (as adjusted for the gear ratio) and the synchros will get minimal use.
You clutch out and continue accellerating --- The clutch did most of the work, thus preserving your synchros.
09-01-2005, 05:38 AM
#22
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For comparison:
Single clutch shifting (normal):
You clutch in --- Same as above, section 1 drops RPMs, sections 2 and 3 still linked and spinning at same speed.
Shift into neutral --- Sections 1, 2, and 3 now all spinning at different speeds.
Shift to next higher gear --- Sections 2 and 3 now need to be mated. However, because of different gearing and slight but different RPM reductions, 2 and 3 need to have their speeds synchronized. The synchros do this, synchronizing section 2's RPM to section 3's.
Clutch out --- Rev matching here will only preserve your clutch and make the transition smoother (less shock to driveline) because all you're doing is trying to get section 1's speed to match sections 2 and 3's speed. The synchros have already done all the work of mating 2 and 3. Now, keep in mind, this is what they were designed for, but they will wear.
Single clutch shifting (normal):
You clutch in --- Same as above, section 1 drops RPMs, sections 2 and 3 still linked and spinning at same speed.
Shift into neutral --- Sections 1, 2, and 3 now all spinning at different speeds.
Shift to next higher gear --- Sections 2 and 3 now need to be mated. However, because of different gearing and slight but different RPM reductions, 2 and 3 need to have their speeds synchronized. The synchros do this, synchronizing section 2's RPM to section 3's.
Clutch out --- Rev matching here will only preserve your clutch and make the transition smoother (less shock to driveline) because all you're doing is trying to get section 1's speed to match sections 2 and 3's speed. The synchros have already done all the work of mating 2 and 3. Now, keep in mind, this is what they were designed for, but they will wear.
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