I've replaced mine with the tires that fit the Smart car! Kumho Solus KH 16 175/55 R 15 Fronts, Kumho ECSTA AST 225/50 R 15 Rear. Will be replacing my wife's ST tires with these soon as well. Have had constant problems with the stock tires, found they would actually change shape when they warm up (even in cold weather) and the affect was as if they had gone out of balance. Even used large amounts of ceramic balance beads and they were still bad. No problems at all with the new Kumhos, 1,800+ miles on them so far.