i have the 17 on mine. thought about 18 but i dont want to lose any oomph. plus with the 17 you can still pass the 120 mark on the speedo

Frank

(Former)05 BA tbike pipes, ai removed, Freak, mikuni hsr 42's, 904, ported/polished head, 1mm oversized valves NOW-2010 silver and black tbird