Renthal 257-520-13GP Ultralight 13 Tooth Front Sprocket When looking to replace your front sprocket, Renthal front sprockets are an easy choice because of their strength and inexpensive price tag. Also known as "chainwheels", Renthal front sprockets are precision manufactured to withstand the rigors of supercross, motocross, and enduro racing. Renthal Front Sprockets are made out of 655M13 nickel-chrome-molybdenum alloy steel. What does that mean to you? Ultimate strength and hardness. Self-cleaning mud grooves prevent the build up of dirt.