Originally Posted by
Syscrush
This is surprising to me - I think you'd flex the frame and crank arms more than you'd stretch that belt under pedal power. Maybe there's a bit of deformation of the rubber around the teeth while the carbon inside stays intact.
I don't think those belts flex (stretch) or deform either. Perhaps it was not set up properly on the bike. Unlike chains, which need to have some slack in them, those belts need to be setup fairly tight so they feel like rubber bands. I've got belts on my two Harleys, and they provide a very responsive drivetrain.