I was reading about MWERKS 135 project car. I was suprised to hear that they changed tires to Yokahama S-drive summers and found the grip decreased compared to the stock runflats. They said the runflats did a good job of getting traction off the line compared to the new tires. However, the ride quality was improved. Here's the link:
http://www.mwerks.com/artman2/publis...-_Part_2.shtml