You guys have helped me out before...i know if you have 31'' tires you should use 33 teeth...32'' tires you should use 32 teeth..what if you have 31 1/2 tall tires which one should i order my speed shows 4-5 miles slower than gps reads...so when i'm going 60 mph..im really going 65 mph on gps.....thank's for reading this post...