@spychic I've been riding on the Duro median HF903?4 tire for about 7 months now, I think the best compensation for the larger circumference is to go up two teeth in the rear sprocket. I went up one tooth but I feel like two tooth would better hit the powerband at highway speeds, and also provide more low-end grunt in first and 2nd gear. And the Doro definitely raises the back end a bit, but you can compensate by adding a 3/4 to 1" PVC spacer into the top of the fork tubes (search the NX250 posts for more instruction there), or I bought some CRF230L front fork Springs and cut them down to about 1" inch longer than stock Springs (also see other NX250 posts on the subject). Either option will raise the front end a bit to compensate, not to mention that the stock fork's notoriously soft so it's probably a good idea anyway. @arescec You might also want to check and make sure none of the little o-rings fell out of the carb when you were cleaning it last. I about lost a tiny o-ring on the idle mixture screw which shot out while I was blowing out the carb orifaces with compressed air.