Fresh off installing the new OS Giken limited slip differential it was time to return to where our wheelspin issues first surfaced – Grissom Aeroplex in Peru, Indiana for the 2011 Great Lakes Divisional Championship. It was at this event last year that we discovered wheelspin with the OEM limited slip differential. So we thought it only fitting to head back to the grippy concrete to test out the new LSD.
With the new differential in place we noticed an immediate change in the feel of the car, with improved stability and traction from the Hankook Ventus R-S3 tires at the rear of the car. Slaloms felt more stable, and we were able to get back to the throttle sooner and harder than before. The change did bring with it moderate understeer during initial turn in and high-speed power-on sweepers. Team drivers Chris Harvey and John Rogers didn’t let this get in the way as they held down the class lead after day one, with just 0.050 seconds separating the two drivers with Rogers out in front.
We tried changing the rear anti-roll bar setting, but found it unsettled the rear of the car during corner exit acceleration. So to help get the rear of the car more involved in turning the car during initial turn in and power-on sweepers we decided to install stiffer rear springs. A Sunday morning swap of the rear springs on our KW Clubsport coil-overs in the paddock took about an hour, which turned out to be time well-spent. Both drivers felt the change, noting better initial turn in as the higher rear spring rates moved some work from the front to the rear of the car. Power-on understeer was virtually eliminated, with transitional balance still very stable. With both drivers adapting to the change, day two runs came down to fractions of a second to decide the winner. Harvey took advantage of a rerun to pass Rogers for the day, but it wasn’t enough to erase the deficit from day one. When the dust settled only 0.012 seconds separated the two drivers with Rogers taking the win.
Our next stop will be the Tire Rack SCCA Pro Solo Finale and Solo National Championship events in Lincoln, Nebraska just three short weeks from now. There we will put all of our work on the Mazda MX-5 project car to the test.