38″ is good. 36″ is a better goal using the 36.5″ New Concept nose if you can find one. L-4 and/or L-3 as others have stated is the best place to start for pipe. I highly recommend the Hoosiers in the R60 compound and the 4.5/10.5-6 size on all four corners. That tire set up is what won the WKA sprint class on day 2 at Daytona last month (he wasn’t running Yamaha though). You don’t really need the wider tire on the rear unless your chassis is just really hard on tires.