I need more gearing info!

[Big Wig]

I finally got my gearing where I like it on my XXX-T (on my track anyway): Stock 88 tooth spur and 16t pinion. Well, I'm having a problem with pebbles getting in and wrecking my spur gear! The only other spur I have for this truck is an 84 tooth - what pinion should I run to get close to the previous 88, 16 gearing? AND, how do I figure such a thing out?

thanks
Jay

[Nairb]

It should be 15/84. At this ratio, 4 spur teeth are equivalent to 1 pinion tooth.

[kojak61]

http://www.webphix.com/rcsite/default.asp
try the gear ratio finder on this site. Punch in the gear ratio you are using now and it will tell you all the combonations that you can use.