Thats a good question. I always wondered why they have a spread for racing oils but aparently start up wear is significant. In fact, up to 50% of most wear is at start up according to what Amsoil just posted on their pre-oiler data sheet. For me, I'd only go as far as the 5w-40 which is a 35pt spread. For racing I'd rather use a solid 10w-30.