When I first changed to PR2's with a 50 series rear tire and put on the CS-One, I finally had the confidence to let 'er rip to 170 indicated on GPS in 5th gear outside of Hemet, Ca.. A little disconcerting was the Gen II windshield when it was furiously flapping around. After a return run in the opposite direction, I couldn't muster over 165, so there must have been a wind factor also. This year with a 55 series rear tire outside of Searchlight, Nevada, the bike wouldn't pull past 165 in 5th, so I imagine this is pretty much the limits. It gets to 140 in 4th very quickly though, and this engine sings a beautiful opera at 10 grand.