well I'm not so sure that they are that much softer. Those Autcross specific tires have insanely stiff sidewalls which substantially increase the weight, which could explain the reduced straight line acceleration. But the reduction wasn't just marginal it was significant. Perhaps its something to do with tire temps as well. I noticed in between Autocross runs that car was susbtantially quicker out of first gear than when the car had to sit for a while and the tires got cold again.
I mounted my BBS RK (20 pounds) with Kuhmo Ecsta Supra's which were roughly the same weight as my Autocross wheels(12.5 pounds) with Falken Azenis. Both were about 40 pounds but the straightline acceleration of the BBS wheels was much much better. But those Kuhmo tires were absolutely a nightmare on the Autcross course. More like drifting tires
