Yes, the treads are cosmetic. they dont move. Some weight of course but otherwise not a factor. Think the losses in the gear box, and the relatively light weight design of the gearbox is the primary problem right now.
Question: Does the tank get to a usable speed with the parts you are using right now? Or does it strip the gears and stop moving? What is the turning radius with the parts you are using right now?
And btw: the book wikinomics is an excellent read about design collaboration like this group is doing...in your copious spare time, consider reading