The tracks are fiber reinforced plastic, but I have replaced them with a set of metal tracks from http://www.rcpanzer.de. There is nothing wrong with the kit tracks I just wanted a set of metal tracks.
The wheels have brass bushings, not ball bearings. Works fine, no problems.
Upgrades!!!! PLENTY. http://www.backyardarmor.com have new suspensions for the Tigers, they also have aluminum barrels and metal tracks, and the kits them self.
http://www.customrcmodels.com have reduction gearboxes, GREAT stuff.
I had a problem with the gun elevating mechanism, but I got around that with some micro switches. It would be difficult to give you the details here, but if you are lucky you can find it rcpanzer.de.