OK Steve , its like this . The bike's performance /acceleration really quickens. I stated that I thought it could reduce the quarter mile time by 1/2 second. I was not joking . BUT , the fuel mileage is reduced and revs are up everywhere I ride it. I take a lot of trips and my normal cruising speeds have the revs up 300 to 400 rpm . BUT , if you are looking for a performance enhancement this is it ! It hustles through the gears . The speedo reads way high though , 62-63 reads 70mph. Raphi is the only member I know who is running a 17T full time. You can PM him. I have not seen Raphi around lately.