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Opentracking.com recently purchased 4 of the new Kumho V10 road course tires. (2) 275/40-17 and (2) 315/35/-17. The 275's were purchased for the front of our Z06 and the 315's were purchased for the rear. The first thing we noticed was how the tires looked like the Hoosiers. No tread pattern except for the two Hoosier like inboard grooves. The other thing we noticed was how the outside edges rolled over dramatically. Meaning the outside edges are very rounded on the Kumho V10 while the Hooseiers appear to have a slightly sharper radius on the transition to the side wall. Seems like this takes away from the actual contact patch of teh V10's but it also seems like it may reduce the cording on the outside edges that seem so common on the Hoosiers.
Since our 315 rear Hoosiers finished their life during our last track event at Buttonwillow Raceway...we mounted up the new Kumho V10's and hit the track with Hoosiers on the front and the Kumho V10's on the back. The cold tire pressure was 30 psi. About halfway through the track session the rear of the car became very unstable. The car felt loose and unpredictable. The rear V10 tires felt like they were sloppy and slow to react. They felt like they needed more air pressure but when we came in from the track we found the psi had risen to more than 38 psi. We noticed that the Hoosier side wall was stamped with a max psi of 44 while the Kumho's were marked with a max psi of 51 psi. So after considering the sloppy slow reacting characteristic we thought maybe...just maybe they want higher psi than the Hoosiers. We added more air....about 5 psi. This made the tires behavior even worse. It was now time to use the low tire pressure concepts that we previously learned when running the Kumho Victoracer's many years ago. We targeted hot measurements at 29 psi for the rear and 32 for the front. Lowering the psi transformed these tires into stellar performers. They felt terrific at the lower pressures. The difference was so dramatic that it was hard to believe they were the same tire. Our conclusion was that the tires face was rounding outward under the initial higher psi levels. Thus we theorize that the tire face had a crown effect with the higher psi. We suspect that the tires were running on a high center when the psi was at 38 psi and above. Having lowered the psi.......... the tires became stable and consistent. They stayed this way through the entire session and stuck like glue. We ran the tires for 1.5 days at the track and found them very rewarding and very competitive to the Hoosiers. Considering the tires are significantly less expensive than the Hoosiers and considering the high level of performance.......we plan to buy more. Plus according to Kumho technical support....you can drive them to the track. That is something you can't do with the Hoosiers. We can't wait to mount the fronts to see how our Z06 feels with V10's on both ends of the car. Stay tuned to our website for the update on having V10's on the front and the rear of our Z06. President Opentracking.com |
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