Originally Posted by OverGeared

The stock spur is 48pitch as "over gear" had answered.
Your FDR (Final Drive Ratio) should be 4:1 if running a 17.5 Spec motor.

For the 80teeth 48pitch spur you can use a 38teeth 48pitch pinion gear, however, I doubt if the adjustment slots of the motor mount could accommodate the motor with the 38T pinion. That being the case, you might want to change the spur to 76teeth 48pitch and use a pinion of 36teeth to have a perfect gearing of 4:1. If the 76teeth spur is not available you can opt for the 75teeth 48pitch and still pair it with a 36T pinion gear.

Hope this helps.