Ultra - Light ULHP - 32 straight vane rotors provide an excellent balance of efficient cooling and lower rotating mass on hard braking dirt tracks or rear axle service on pavement cars. UL rotors are cast from premium grade, long grain carbon iron for long wear, high thermal stability, and resistance to distortion. ULHP - 32 rotors offered the added performance and smoother operation of precision turned faces with less than .001 variation in flatness, parallelism, or run - out.