May 21, 2007 update to the Mazda STS2 Miata project car

Another notch on the gun at Texas Tour

Gridded up and ready to go in Houston

This past weekend in Houston brought us our third STS2 National Tour victory this year. It also gave us an opportunity to test and compare the performance of the two new sizes of our Bridgestone Potenza RE-01R tires.

Before the event, we visited our friends at Soulspeed to mount up the 195/50-15 tires and then took them to a local parking lot to run some circles and put a heat cycle on them. The 205/45-16 tires that we ran on in our initial test session at Mineral Wells, and then competed on at Walnut Ridge were barely showing any wear despite having some 40 laps on them. We used the Test and Tune course at the Tour on Friday to do out comparisons. It consisted of a slalom with 63’ spacing, a crossover, a huge sweeper with camber changes, back through a crossover, and then a series of large offsets into the finish. This gave a good mix of transitional elements, steady state cornering, and acceleration zones.

After spending two hours on the course instructing others at the Cone Clinic, we were quite familiar with the layout. Given that, out first four runs on the 16” tires were extremely consistent, all at 26.6 seconds. Next we mounted up the 15’s and went back out to turn 26.7, 26.5, 26.3 & 26.4. Noting the better results, we went back to the 16’s to bracket the test and turned 26.4, 26.5 & 26.6. The 15’s were certainly no worse than the 16’s, and looked to be slightly faster. That said, the 15’s were fresher so there may have been an influence there. One good piece of news is that the two sizes had similar steering feel, so it will be easy to swap back and forth depending on desired gearing.

With testing done, it was on to the competition. The courses each day had a good mix of large sweepers, and transitional elements. Given the lower-grip surface, we had to disconnect our rear sway bar to stabilize the car and put power down. After the adjustment, the car was a dream to drive. Not only were we able to take the STS2 win by quite a large margin (3 seconds), we beat a strong STS class for a change. In fact, we finished 4th overall on the PAX index.

Next up is the Huntsville National Tour in two weeks.

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