Whats a mod1 pinion?
 

Need to buy some pinions for my revo conversion with stock tranny. Do I need 48 pitch or mod1?

Also, what size pinions are recommended for a 9xl on 5s? It has 38 tooth spur. Thanks!

Nitro spurs are mod 1 so you will require a mod 1 pinion
http://www.rc-monster.com/proddetail...1pinion&cat=40

Gearing info: http://www.scriptasylum.com/rc_speed/_top_speed.html