I blew a tire recently and had $700 damage to the TT. The service manager explained to me how to tell when the tires need changing. He said when a tire is good, the tread is flat across the tire. When the tread across the tire is no longer flat across the tire, but is showing a curve across the tire, the belts in the tire a separating and the tire need changing before a blowout occurs. We checked the tires on my TT and sure enough, the new tire I purchased to replace the blowout was flat and the other three were curved. The TT is in storage for the winter, but in the spring it will go to the tire store for a change of tires to Maxxi's before anything else gets done.