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Mazda MX-5 Miata: Project STR Faces Tough Competition Jul 13, 2011

Our lead project drivers, Chris Harvey and John Rogers, recently pointed the red Mazda MX-5 toward Toledo, Ohio, for the Tire Rack SCCA National Tour. The event site is one of the best you’ll find east of the Mississippi, with lots of room, smooth concrete and high grip. The two-day, combine- time event featured 50-second courses that were fast and relatively wide open. Our onboard Race Technology data logger showed that nearly 40 percent of each run was spent at full throttle—about double what we find at most events.

Our car has displayed a tendency toward power-on oversteer at nearly every venue it’s run in the past year and a half—until now. On day one of the championships, the story for us was massive understeer. The rear end was locked down in transitions and would not slide, no matter how much we provoked it. This ultimately limited how early we could get back to the throttle, killing our speed at the end of each straight. The rev-happy Honda S2000 CR of Geoff Walker showed everyone in the 23-car STR field just how quickly the course could be completed, leaving Chris and John in fifth and eighth place, respectively.

Car balance improved on day two thanks to the now-rubbered-in course as well as adjustments to our KW Clubsport coil-overs and driving style. Rogers was able to post the third-fastest STR class time of the day, with Harvey just a 10th of a second behind.

While sorting out the mystery understeer issue was somewhat frustrating, we realized two things. One, we now have some tuning tools in our toolbox to solve future handling issues. Two, this is not Lincoln, Nebraska, where the National Championship event will be held only weeks from now. We’ll be sure to read through our logbook from prior trips out to Lincoln and figure out how to optimize the car for that location.

Comments

jaball77:
What kind of alignment are you guys running on the car? My car has a slight tendency to understeer as well, even with 0.3 degrees LESS camber in the rear (-1.9 front, -1.6 rear, 0 toe F&R). I'm guessing it has something to do with the massive amount of camber the 5-link gains as it compresses… There's a camber curve over on Miata.net somewhere… Next time I get it aligned I'm going to try for a 0.5 degree difference front to rear and see if that helps… Jason Ball
Jul 14, 2011 12:39 p.m.
WoodyatTTR:
Jason: We have a similar difference in negative camber front/rear as you do. For us, this was the only event in nearly 2 years we have had this sort of steady-state understeer. So we won't chase our tails over it. Most often we have good transition balance, decent steady-state with just a hint of safe understeer, followed by power-on oversteer. We used the compression adjustment at the rear and some rebound in the front to free up our car in transition. We changed how we drove to keep the car transitioning as often as possible - by trailbraking into the turn and getting back to the gas (even a little) as soon as possible. This minimized the time spent coasting steady-state at the apex. Even with the settings we used to free up the car it wasn't challenged in fast transitions.
Jul 16, 2011 8:21 a.m.
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