Originally Posted by Darth Lefty

The roller you see under the back pulley is not a tensioner. I think it's just there to capture the belt... the C-Drive website shows some bikes set up without it. Tension is set with screws going to brackets in the dropout slots, and as it came from the factory it is quite tight (spec is 20 kg tension according to the manual). The C-Drive website also shows some bikes set up without the dropout tensioners but I imagine that's a pain in the butt for the mechanic.

The only lash I felt was the action of the brake itself. So far as how well I can modulate the brake, I can't say. I'm still on the learning curve, I think I haven't had a coaster brake bike since I was nine or ten. I don't know what the elongation of a drive belt normally is but I would believe it's similar or even less than a chain. Kevlar elongation at the breaking point is only a few percent and I imagine other fibers that they might use have similar properties.