This method certainly works to smooth out the low-rpm shifts, but I was under the impression that rolling onto the throttle while releasing the clutch was bad for the clutch? Please correct me if I am wrong.
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Originally Posted by jphughan
The RPMs at which you shift determine how much (if any) throttle you should be adding before the clutch engages. The reason for this is that the rate at which RPMs fall while the clutch is in is pretty constant through the rev range, but the difference between RPMs between gears at a given speed increases as you go higher in the rev band.
So for example, at 40 MPH in 1st gear you're probably turning 8400 RPM, and at the same speed in 2nd gear you're turning maybe 6400 (not sure about that, but it'll work for the example). That means that there's a 2000 RPM difference. So as long as you can complete your shift in the amount of time it takes for the engine to lose 2000 RPM, you're good without applying any throttle during the shift.
But let's say you shift at 15 MPH. In 1st gear, that might mean you're turning 2500 RPM, and in 2nd gear that might be 2000 RPM. That's only a 500 RPM difference, but given that the shift itself takes about the same amount of time, the engine will fall below the optimal engagement RPM in that amount of time, so you need to add some throttle prior to clutch engagement there to slow down their fall or even bring them back up to where they need to be for a smooth shift. Think of it as rev-matching on an upshift.
Generally speaking, the higher up in the rev range you shift, the less throttle you need because the more time you have to shift due to the higher differences between RPMs in the gears.
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