I weighed mine and the tire/wheel combo is 5 lbs less than my stockers, and I have the same as MikeR. Plus add the less rotating mass into the equation from 19" to 17". I think that's a big difference. I've noticed at the track they gave me more room for error. Before when I launched too hard and spun more, I could lose up to 1 whole second. Now when I spin instead of hooking up, I lose the most about 2 tenths because they grab faster. That's a huge difference in my book.