Ary,
Thank you for sharing this valuable information. I never considered there would be gear compatibility issues with Slot.It gears. It does make perfect sense that you cannot maintain a pinion pitch by varying tooth count in a same diameter gear. If you machine the crown hub to eliminate the ridge, it would be possible to run a 10 tooth 6.5mm pinion with any Slot.It crown gear, but since gear modification is not legal, we couldn’t race with that combo.
Jim J.