There's some interesting reading on sprockets at the F650 faq site: http://faq.f650.com/FAQs/SprocketsOtherSizesFAQ.htm One suggestion for people contemplating a 46T or 48T rear is to try 47, if such is available. 47 is a prime number, so that should even out wear a little and also reduce sprocket flex (if this is an issue, I don't know) and vibration. The stock R 43T is also prime:thumbsup: 13 is prime too, which is great for the stock front. There's some info on the linked page about small front sprockets, with a very telling graph. 12T is getting pretty high up on the vibration curve. 13T is bad enough. I've been thinking about a 14T front sprocket. It looks like it might reduce vibration a little, being a little larger. I'd like to leave the size of the rear sprocket alone, since I like the speeds where the max engine torque comes out with 14/42. WR250X speed in mph at 8000 rpm (approx. the max torque output): Gear 13T 14T 1.......21..23 2.......28..30 3.......41..44 4.......52..55 5.......61..65 6.......69..75 Also since 13T>14T is about an 8% change, I hope my speedo is very close to correct without a speedohealer:) Theoretical top speed at the rev-limited 11200 rpm with 14/42 is 112 mph, exactly 1 mph for each 100 rpm. If acceleration is too bad, I can go to 43T or higher. Or I could lose weight. Each additional tooth is 2.4% (44/43). 290lb + 220lb = 510lb. 510x2.4% = 12 lbs per tooth:D EDIT: Wow, looking at the table now, it looks like first gear is too high - out of line with the others. I would like 1.......16..17. How hard is it to change one gear?