Grassroots Motorsports
Issue link: http://grassrootsmotorsports.epubxp.com/i/501675
Grassroots Motorsports 122 FEATURE: STREET TIRE TEST Testing tires takes more than just tires. You need a car, timers, and mounting and balancing gear. For today's test, all tires were in the 205/50R15 size and mounted on the 15x8-inch 6UL wheels made by 949 Racing. Tires were unshaved. You can't effciently do a test like this without a small army. Kim Whitener worked the timers and recorded driver impressions, while Forrest Windecker at Texas Track Works handled the onsite mounting and balancing. After each set of runs, there was always a fresh set expertly mounted and waiting for us on the alter- nate wheels. Gerry Terranova then stepped in to get tires installed quickly during post-run driver interviews. The crew ran like a well-drilled military unit. Early Skirmishes Our frst hint of each tire's performance came on the skidpad. When testing tires, we frst run three laps in each direction to scrub off the mold release and awaken the cold rubber for duty. To determine optimal tire-pressure ranges, we then run each tire around the circle under maximum load for three laps at time. We start at 40 psi and then drop pressures by 4 psi until performance drops off. We then go back to the indicated optimal pressure and retest to confrm the data point. We measure performance strictly with a timer–no pyrometer–since we've found it provides more reliable results. We glean additional data from relative lap times between tires, a leading indicator of steady-state grip. Information about each tire's heat tolerance also emerges as they endure heavy loads for a solid 30 seconds at a time–no respite. We cool them as needed with a water sprayer. Once we have our ideal pressures, we move to the test course. For this day, we chose to do two-lap runs in sets of three for each driver. That put the total time in the typical 50-second autocross range, while allowing for split times to examine heat characteristics and mine for a fyer performance. The test course is fairly busy, so putting two blazing laps together is a challenge when drivers are running for hours. In addition to retesting a control tire at the end of the day, we also inserted it into the middle. This verifies that the course or driver isn't getting better throughout the long session, as can often be the case. We used the winner of our last test, the BFG g-Force Rival, as our control. Fire at will!