XTR SMRT97 pro level rotors are both high performance & lightweight&44; using the proven Shimano Centre-Lock system giving increased strength & security with an easy set-up Precision cut & drilled heat treated stainless steel braking surface improves pad clearing in muddy conditions while aiding cooling under high load Large 4-arm alloy spider is a highly rigid & lightweight support for the rotor surface Super polished braking surface gives excellent braking performance For rear use in conjunction with XTR M975 front calliper Average weight 105 grams