Quote:
Originally Posted by anticubus
Take a 1 -> 2 shift at 4000RPM before we account for final drive:
1st gear output is ~14400RPM (~3.6 x 4000RPM)
2nd gear output is decoupled. 2nd gear input is spinning at 4000RPM, so the output gear that the fork will mesh to select is spinning at ~8400RPM. Adding in the connection to the wheels, you need to account for the engine speed that matches the rotation of the wheels after final drive, and that's the sweet spot for each rev-match up or down.
That's a 6000RPM output speed drop, and not only that, but the selector fork will have all the momentum from 1st gear output spinning it at 14400RPM as it gets slid over the 2nd gear synchro and against the mesh teeth spinning at 8400RPM.
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First off, thank you. Let's talk about the gear ratios. That 3.6-to-1 ratio is 3.6 revolutions of the input shaft for every single of the output.
input 4000 -> output 4000/3.6 = 1111 (ish) RPM. Follow down for the rest of the gears.
That doesn't invalidate your observations overall, especially the whirring sound you hear and resistance felt when downshifting into second and especially first. The reason that sound is important is because for any shift, the input shaft is being driven by the output via the syncro clutch. The lower the gear, the greater the mechanical
disadvantage through which the syncro clutch must drive the input. The viscous drag of the gear oil is amplified in the lower gears, and the syncro clutches in this transmission are as compact as possible for a conventional gearbox. There's more to it. The layout of the gearbox with respect to what the 1-2 syncro clutches must drive also plays into the picture.