Friend of mine went to Aus for a few month and was working with a performance tyre company. On track days they'd bring their mobile truck down and I think it was Michellin but not too sure, but he said that they stocked a prototype tyre that when the tyres were worn down, the customers weren't allowed to keep them because of the technology and secrets used to build them!!! They'd special bags in the truck that the used tyre was placed in and sealed and then returned to the factory!