Mar 19, 2007 update to the Mazda STS2 Miata project car

Learning from your mistakes

Wow, what happened? One minute we are starting the new season right where we finished last season with a National Tour win at Dixie, and the next minute we are mired deep in the field with an ill-handling car in San Diego. Here’s how it all happened and what we are doing about it.

A week prior to San Diego, we hauled up to Dallas for a test day on a smallish grippy concrete lot. We continued playing with staggered tire setups and found that running the Falken RT-615 in the 205/50-15 size on the front gave us better times than running the 205/40-16 in that position. The car had more grip up front and lost little of its responsiveness. We used the 16” size in the rear for all runs for better gearing and progressive breakaway. Given those results, we used the same setup for the Tour stop in San Diego.

At the Friday Test & Tune at San Diego, the handling was excellent with good balance in the sweepers and good stability in the transitions. Of course, the T&T is held on a different lot than the actual event with a tighter course. The lot used for the Tour at Qualcomm stadium is very unique in that there is a huge hill across which about 80% of the course runs. Every turn ends up having some sort of camber change which alters the characteristics tremendously. The surface itself is fairly unique with old, well worn asphalt that has a lot of exposed aggregate. The aggregate stones, though, are polished from wear. This puts a premium on adhesive grip favoring R-compounds and wider tire widths.

The other unique aspect of San Diego at this time of year is the weather. A cool, damp “marine layer” typically hovers near the coast moving inland as the winds pick up. This can at times keep it quite cool during the day.

The locals, of course, know all of this. Their cars are setup for it and they make sure to have co-drivers to keep some heat in the tires (contrary to some tribal wisdom, our experience is that stone cold Falkens do not work well). They also have the experience of running up and down the hills of Qualcomm, where only a limited number of overall course design flows can be accommodated due to light poles and Jersey walls. See where this is going?

Running 5th heat, we assumed that it would be warm and a co-driver would not be needed. Wrong! Instead, the event ran long each day, and it was quite chilly when our turn to run came. The first day, the car was almost undriveable with major stability problems every time we touched the throttle. Maxing out the front shock rebound and minimizing the rear helped a bunch the first day, but we still had to deal with cold tires. For the second day, we brought tire blankets to at least maintain some heat between runs. We also disconnected the rear sway bar (stock 12mm). This helped some more but was not nearly enough as we ended up way back midpack.

Disappointed in our on-track performance, we still had lots of fun with the comraderie of the STS2 crowd. Sharing setup info, we learned that both of the front-running cars were running the same sway bars and front springs we were, but used 25% less spring rate in the rear (350 vs 450). They also were on relatively full-tread tires which may have heated up faster and been able to get more mechanical grip on the exposed aggregate of the racing surface. For sure, we were out-driven, perhaps because of local lot/course experience and probably just shear talent. Or maybe we just had a bad weekend.

One of the things we teach in our autocross schools is to revel in your mistakes and misfortune because that’s how you improve. If you can’t recognize or admit errors, you’ll never make changes for the better. So that’s the attitude we take as we store away this information and look ahead to next week at El Toro in Irvine, CA. With three run sessions in the Pro Solo format, we’ll have plenty of time to determine whether the problems were a one-time deal or whether something in our program needs to be adjusted.

On a side note, Bridgestone had a major presence at the San Diego Tour, bringing out their 18-wheeler race support vehicle. We spent some quality time with some of their folks who let us know that they are planning to release two new sizes of their autocross and drift-proven RE-01R that will be of major interest to the STS and STS2 crowd. One is a 205/45-16 which is about 23” tall and 7.6” wide (tread), which are similar dimensions to the 205/50-15 Falken. Also, they will have a 195/50-15 with the same overall specs as the 205/40-16 Falken (22.5” tall, 7.2” tread). In addition, they plan to have support at one other National Tour and at the Solo Nationals. All of this is great news for the sport and we look forward to testing some samples of these new tires in the upcoming weeks.

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