RENTHAL REAR SPROCKET 42 TOOTH CBR600 F4i CBR RC51 Renthal Ultralight rear chainwheels are manufactured to exteremly tight tolerences from a special material developed to withstand the rigours of Supercross, Motocross and Enduro. The 7075 T6 aluminium alloy rear chainwheels are 66% lighter than steel, yet incredibly durable. Their advanced tooth profile, concentricity and accuracy of fit provide maximum power transfer and long-life. Renthals combination of a very high strength base material and an exceptionally hardwearing surface result in significantly increased chainwheel life