I was under the impression that with the stock gearing, the speedo was pretty darn accurate. I put on a 14t front sprocket and went for a ride with a GPS to test. As I expected, the speedo was off and read high, but by about 9% and not 7% like I expected. I never measured the stock speedo with GPS, but I'm guessing it reads about 2% high. That's still pretty accurate, but not dead on like I expected.