What is the adjustment on the factory Timkens again? If you set it on the tight end of the tolerance, I don't think there will be any problems when using disc brakes and with a floating caliper, there shouldn't be any problem at all. Now, are there floating calipers available for a rear disc upgrade? I don't know since I've never used a rear disc setup and really don't see a need for it unless you plan on hitting the road course with a vengeance or live in the mountains...