Need more information...So, now we have "some"...
Motor size... "motor is a briggs 12hp flathead"
Tire size... "tire sizes front 5inchs rear 6inchs".."and the tires a go cart racing "...
Trans or transaxel... and a tranaxel
Class your racing... S/P class
Type of Track, length... the track is oval dirt and i think its a 100ft straightaways
So it sounds like you want to set up for a basic dirt track in the S/P class, running a 12 hp briggs and a trans axel...
An importane concideration is your tire and wheel choices...tire circumfrence IS part of the gearing equation...So you'll need to be set in that...unfortunatly, in the S/P class you can NOT run go cart tires, and will need an 8" minimum rear rim...
That will put you about 15"-16" in tire size...
With the "transaxel", the gearing comes from the trans you have and the pully setup...SO...
Still need to know what the gear ratio is of the trans axel you plan on running...is it a 12:1 or a 9:1...? that will make a difference in the pully choice...
You will also need to set up a "Jackshaft" to get belt power "up" from engine to the reset axel height and some pully/gearing adjustment can be made there as well...
