Originally Posted by
goin2drt
Sorry. Coming from 21.5 now going to 17.5 and was looking for actual gearing suggestions, pinion and spur. Sorry not clear.
You'll certainly need something smaller than the kit spur. This gear chart here shows what will mesh:
http://abram.eu.org/gear_tc6.php
I'd start with your 21.5 gearing and increase the FDR by 0.5 to 1.0.