Fiberglass belts (coated with PTFE) do not track well on systems using crown rollers. The lack of stretch in the belt material, when running on a crowned roll results in a very tight belt center, and loose, wavy edges.
Kevlar belts (coated with PTFE) have more stretch than fiberglass belts, but the amount of stretch is still quite low. Therefore tracking a Kevlar PTFE belt is possible, using only crowned rollers as the tracking mechanism.
To succeed, the system should have good roller alignment and take up rollers that can be used to manually adjust the tracking. The amount of crown should also be kept to a minimum.