These direct replacement shoes are lined with Carbon Kevlar material that is both bonded and riveted for added strength. Carbon Kevlar material provides superior stopping capability combined with a very drum friendly nature. We believe the R4 compound to be one of the best all-around compounds for “Full Race” competition use. Optimum operating range is 450F to 1200F. This compound “beds-in” quickly so you can concentrate on driving at speed almost immediately. Also available in a High Performance Street and Autocross R4S compound. The “S” compound is very fade resistant and is good for autocrossing, some driver’s schools, solo events, and rallies.