Front Sprocket: smaller for better acceleration/bigger for more top end. Rear Sprocket: Smaller for more top end, bigger for more acceleration. If you ran an A55 motor with a 40 tooth rear sprocket you would probably be able to pop wheelies, but you would top out at like 20mph. What are you trying to achieve? Top speed A55 the biggest ratio you can go is 28front, 20 rear. That will require mod of the case, and a grind on the rear wheel. Hope this helped