Originally Posted by
sosidge
75T/48 is the same diameter as the kit 100T/64.
One point to consider is that any pinion over 30T/48 won't slide easily onto the motor without bumping the top deck on the way, so it's worth basing your spur choice on that.
Thanks.
So the smaller spur is better. That way it is less likely to run into that problem. As long as you can get the desired gear ratio.