I do a fair amount of woods and trail riding to get to my practice track, and I noticed my '07 450 seemed to be geared a bit high in second gear. I seemed to be stuck between 1st and 2nd in the technical trail stuff. I decided to swap to a 51T Renthal, and I am very happy with the results, I was a bit concerned I would loose my beloved smooth power low to mid from this swap, but on the MX track, while I did gain some snap, the power is completely controllable and smooth. Great upgrade for $55 !!