Michelin Desert Racing Front Tire - 90/90R-21/Blackwall Excellent durability, even in high temperatures. DOT-compliant, so you dont have to trailer your bike to the trails. Exceptional stability under braking, with strong lean-angle grip when accelerating. Rear casing engineered to reduce operating temperature and improve tire life. Front tire load index and speed rating 54R, Rear tire load index and speed rating 70R. Michelin size 90/90x21 = 80/100x21 Conventional sizing. Michelin tire size 140/80x18 = 120/100x18 Conventional sizing.