The 39s obviously don't grip as well as a semi slick track based tire but the ku39s are seriously good especially when you consider the 888s are almost four times as expensive when you factor in how long they last. I expect to get about 10,000 miles out of them whereas my 888s were shot by 5,000.
Very progressive breakaway and great feel and feedback from the tire. On a dry track they gave very good grip and were good in braking as well. Only done a few 100 road miles on them, already thought i feel that I will almost certainly be buying them again as they tick the box for my track and road use.

