What rim are running right now? It ought to pull a 28-32" bar just fine wearing a 7-pin rim and under 28" is purely 8 pin territory. If you're wanting to speed the chain up, relative to the engine RPM (drop in overdrive for an analogy) then you want to go higher in tooth count, to slow the chain down you want t go smaller. If it helps, thin about a 10+ speed bicycle, only in this case the rear sprocket is the bar-tip sprocket, and the rim is the front crank-set. This is assuming that you have a bone-stock saw in good health. Give it a M.M. or a woods-port ad you might stick with an 8-pin for 28" and less depending on the wood you're cutting.