Every 03 Cobra I've seen at the dealers has always been missing the nubs on the rear tires. All of the front tires have the nubs. At first I thought that maybe rear wheel drive cars stress the rear tires and wear the nubs but then I checked out a couple of other non-Cobra Mustangs and the rear tires had nubs on them. I even saw one 03 with only four miles on it with no nubs on the rear tires. I think the loaders are still doing giant burnouts on the 03 Cobras.