nderwater PowerDork
8/10/11 10:17 a.m.

Congrats! What were the pre/post spring rates?

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John "Woody" Rogers
John "Woody" Rogers
8/10/11 11:04 a.m.

Fresh off installing the OS Giken Super Lock Limited Slip Differential, we returned to where our wheelspin issues first surfaced—the Grissom Aeroplex in Peru, Indiana—for the 2011 Great Lakes Divisional Championship. We discovered wheelspin while the car was equipped with the OEM limited-slip differential at last year's event, 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. Both stability and traction at the rear of the car were improved. 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. They held down the class lead after day one, with just 0.050 second separating first-place Rogers from his teammate.

We tried changing the rear anti-roll bar setting, but found that it unsettled the rear of the car during corner exit acceleration. To help get the rear of the car more involved 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, and transitional balance remained very stable.

Both drivers adapted to the change on day two, and deciding the winner became a matter of fractions of a second. 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 second separated the two drivers. Rogers took the win.

Our next stop will be the Tire Rack SCCA Pro Solo Finale and Solo National Championship events in Lincoln, Nebraska, just a few weeks from now. There, all of our work on the Mazda MX-5 project car will be put to the test.

RexSeven UberDork
8/10/11 4:24 p.m.

Cool! Glad to hear the OS Giken LSD is working well. I'm considering getting one for my turbo FC at some point.

Per Schroeder
Per Schroeder PowerDork
8/12/11 8:26 a.m.

For Sunday’s competition runs, we removed the 70 n/mm (400 lbs/in) rear springs and replaced them with 80 n/mm (457 lbs/in). At the front of the car, we are running 100 n/mm (571 lbs/in) springs and a Hotchkis 27mm front anti-roll bar.

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