Maybe they didn't change, maybe cars are faster, more power, driving harder etc. The RR's I've had on the miata look to "wear" 1/2 as fast as they did on the CMC car, after 2 weekends there is a ton of tread left, the HC fall off I don't know yet, but I can only imagine the lower power and weight doesn't take as much as a toll on the tire staying fast. The guy that ran a blistering 1.24.x in a 125hp miata at MSRC was on older tires fyi.