Maybe you'll want to try using a bigger belt size and adding a tensioner to keep it tensioned properly (you can even make the tensioner adjustable!). Timing belts typically don't have lacing options like Conveyor Belts do because they are typically used in high RPM situations, but there are probably some options out there, but I'd doubt how reliable they'll be.
As far as most robots that use treads,
BRECOflex is undoubtedly the most popular choice for robots using treads to drive, Superflex Blue is one I'd recommend. Most teams go with Roughtop/Wedgetop Conveyor Belt Tread from McMaster-Carr when putting tread on their wheels. BRECOflex has a document on treads for robots on their site,
here.