Unfortunately, the KPR S2000’s timing chain tensioner decided that it had had enough, so we ended the day early to avoid a complete failure. The positive side is that we just so happened to do testing during a Redline Time Attack event, and the Zestinos were good enough for a first place win in Street Rear Wheel Drive class!
Since we weren’t able to test as much as I wanted to due to the S2000’s TCT, we went back for another test after replacing it. This time we chose to test at Buttonwillow Raceway in the 13CW configuration. Willow Springs was great to test high-speed cornering grip and behavior, which the Zestinos really excelled in. However, I wanted to test the behavior of the tires on a samplimg of the lower speed corners that Buttonwillow Raceway has to offer. I knew this was going to be another tough test for the tires, since the weather was scheduled to be even more extreme than it was at Willow Springs, with the peak ambient temperature at 108 degrees.
Clint Boisdeau drove the KPR S2000 for the first two morning sessions while I had to drive my Civic racecar for other (non-related) testing, and his thoughts on the tires’ behavior were consistent with mine. I drove the S2000 after lunch, which was in the extreme heat. I don’t think any tire would have been happy at 108 degrees outside temperature, and the Zestinos were considerably less happy on the second day of beating. As a soft compound tire, they are intended to excel greatly during their first few heat cycles. However, despite abusing them in the heat and regardless of being beyond their prime grip, the Gredge 07RS’s never felt sloppy or overly greasy. They are still usable for track day seat time or testing, however they just obviously aren’t as fast after their prime, as is to be expected.
My opinion of the Gredge 07RS is that they are a very competitive street tire for road course track driving in a rapidly growing market demanding the fastest and highest overall grip tires. Time attack drivers that are in a class that require street tires can use them for ultimate peak performance, but be sure to have an emphasis on getting the hot lap done in the first session for the “sweet spot” on these tires. True time attack built cars generally only last 1 to 3 laps maximum, so this is not a tall task to ask from time attack drivers. I think these tires would be great for competitive autocross drivers as well, where tires see quick and intensified heat cycles. These tires would make excellent drifting tires, of course, but that is why they are already established in that market. With several options available for high limit street performance tires, I would rate the Gredge 07RS towards the top in overall fastest peak performance.