My Cannondale has disc mounts, but came with rim brakes, so we decided to add a rear disc brake this year. I bought a set of Avid mechanicals and a disc rotor adapter that threads on the non-drive side of the rear hub. The brake and rotor don't come close to lining up. Are there different thickness rotor adapters available? Shims? Has anyone tried this? I contacted Cannondale, but they were of no help.