MMC will sell you a heavy steel rear sprocket for a fairly sizeable sum of money and it will last well. There is an alternative with the Supermax poly overlay, an American company. Information on www.supermax.net or you can email vyvyanross@yahoo.com Several M3W's have run for many miles successfully with these sprockets. There was another sprocket manufactured somewhere in Europe but I don't think they are currently available, so that is the off the shelf choice at the moment.