From Daytona to Autocross, Part 2 of 2

After competing in the SCCA Match Tour, I (Kenton Koch) learned a lot about the world of Autocross. I was not fully prepared, but will be the next time I head out to the parking lot.

The good news:
The results were much better than expected in my RX-8! I managed to finish second on Saturday to Ron Bauer in the 2016 MX-5 he has been developing with Mazda Motorsports. But on Sunday, I was able to run the fastest run of the weekend against the tough competition. It wasn’t without the help of the autocross community. They were all very kind and more than willing to offer their advice and lend tools where needed. Although I brought everything I thought I needed, I still spent half the time borrowing tools because I either did not bring them to grid or at all.

Items I brought:
•    Tool box with essential wrenches, breaker bar, torque wrench, and sockets
•    Tire pressure gauge
•    Cheap Harbor Freight hand pump (that broke the first time I used it)
•    Oil (RX-8s need this)
•    Jack and Jack stands

Items I will bring next time:
•    Chalk to mark tires to check for tire roll over
•    Water sprayer to spray oil coolers
•    Proper bike tire pump
•    Temperature gun to check ground temperature

Autocross taught me more about setting tire pressures than I would’ve expected. Tire pressures are very important, used as a tuning tool to help balance the car. Since runs are very short (usually under or circa one minute), the tires need to get up to pressure quickly. I learned there is a fine line between having too much pressure and too little, especially with a heavier car like the RX-8 running on a soft tire as the BFG Rival S. If the pressure is too high, then the tire over heats and loses overall grip; but if the pressure is too low, then the tire folds over and again loses overall grip. Pressures also rise and fall quickly given the temperature of the asphalt.

For most of the weekend temperatures remained consistent, which allowed me to find a sweet spot for pressures and an understanding of where to set the pressures to land in the optimal range during runs. However, it warmed up quite a bit Sunday afternoon and I didn’t take that into consideration. The tire pressures ended up way too high by the end of my run, causing the car to be very tail happy. Now I know to pay closer attention to air temperature and track temperature next time. I also plan to speak with the tire engineer behind the Rival S to learn more about this tire. I have experience with BFGs, both on my street car and in the Mazda MX-5 Cup in 2013/14. They make great tires and are great people. Some say the Bridgestone RE71 is the tire to beat, but this last weekend’s Match Tour showed otherwise with the BFG Rival S taking the top 2 steps.

As far as the handling of the car goes, I have some things I want to try to help make the car a bit better. I was struggling with entry stability, mid corner push, exit push, and push induced oversteer. To help resolve these issues, I plan to do the following:

•    Add a stiffer front bar to help with tire roll over, entry stability, slalom stability, and higher mid corner grip.

•    Stiffen the rear damping to help with entry stability and possibly help with mid corner rotation by helping eliminate lateral roll in the rear. This can also help prevent front tire roll over by slowing down longitudinal weight transfer to the front in an effort to keep weight off the front while braking and turning. My current setup is full stiff in the front and 75% in the rear, so this will make it full stiff all the way around.

•    New OEM rear springs to replace the possibly worn out, original springs with 100k miles. If they are worn out, my goal in doing this is to help with mid corner rotation and power down push.

I think this will help get a couple extra tenths and allow me to mess with tire pressures again to possibly gain overall grip. If I eliminate tire roll over, I might be able to drop the tire pressures another pound or so, but I will not know until I test it and see for myself. I like to try different setups and make adjustments to understand how various components affect the overall handling of the car. I have always been very interested in vehicle dynamics, having studied it for countless hours and experimented just as much. Hopefully everything I learned this past weekend will help me beat the new ND Mazda MX-5 in the next autocross! I will be back out there, but most likely for regional events until the next Pro Solo comes around. Fortunately, competition is great here!

Related Content: From Daytona to Autocross, Part 1 of 2