The formula is to divide the J/S In by the Engine and divide Axle by the J/S Out and multiply the two to get the final ratio.
Engine = Clutch Sprocket.
J/S In = 20, 24 or 28 tooth input sprocket.
J/S Out = 14 thru 17 or 20 tooth output sprocket.
Axle = Rear axle sprocket.
For ordering purposes to determine the JS In & Out gears put your desired clutch and rear gear teeth in the proper box and change the JS In gear and JS out gear until you get the desired final drive ratio.
All sprockets are #35 chain.
J/S In Sprockets
24 tooth are primarily for Karts
28 tooth are primarily for Quarter Midgets.