I am not sure about the new compound on the new RT615K model, but the RT615 models were not that great as far as tire wear or traction. I have ran them on my car for the last 1.5 years but would like for something else. I also would recommend an extra set of tires/wheels for the track and one for street.
1990 Nissan 300ZX Twin Turbo 1989 Nissan 240SX Coupe www.JaMallz.com