April 22, 2012

Problem Solving At Porsche NCR

Porsche NCR Club, lined up in grid
Ben and I had planned on running with Porsche North Country Region (NCR) to work out some of the kinks I've been experiencing. This was my first time running with this club at Devens, and it wasn't too bad. I saw a few members from the Renegade Miata Club, but most were unfamiliar faces to me.
Ready to run against some Porsches
Except for the start, the course was pretty fun and straight-forward, with some interesting elements. The weather held long off enough for Ben and I to get some morning runs in. Once the rain began to really come down, our runs were throw-aways at that point. Given how cold and rainy it got, we left after our afternoon worker assignments. I was happy regardless in that Ben got to drive the car as it is now, and got some time to really contemplate what could be changed. There are some results posted over at NCR, but Ben and I only got to take half our morning runs, and skipped out on the afternoon runs.
Ben tearing it up on his second run
For those that missed yesterday's post, the issues we are hoping to solve is that the car essentially can't make up it's mind. The car will begin to oversteer, then suddenly understeer, and then oversteer again. It is as if the front tires can't grip, or don't have enough time to fully grip, where as the rear tires over-power the front tires. When we adjust the shocks a few clicks, the car's behavior dramatically changes (Ohlin DFV shocks allow you to adjust both rebound and compression).
Diving into the sweeper
Below is my current alignment and suspension specifics.
  • Front Camber    -2.5
  • Rear Camber    -2.6
  • Front Toe    .05 out
  • Rear Toe    .03 in
  • Caster    5.0
  • Front Springs    730lb. (13k)
  • Rear Springs    450lb. (8k)
  • Shocks    Monotube, Aluminum-Bodied, Custom-Valved, 30-Clicks of Compression and Rebound Adjustment
  • Front Swaybar    32mm (Full Stiff)
  • Rear Swaybar    19mm (Full Soft)
  • Wheels    18 x 10 +38
  • Tires    285/30/18

Ben and I have some ideas has an idea that may solve some of the issues. Ben is thinking to go with stiffer rear springs, stock or no rear swaybar, and less static rear camber. To verify his theory would work, he suggests lowering the front ride height to change the rake of the front and rear roll centers. I agree with trying less rear camber, but to also stiffen the rear swaybar, keep the rear shocks on the softer side, and to only adjust the fronts. I could always just soften the front-end instead and try that.
Ben Wagstaff himself, with his "Eddie Bauer Edition" Miata
Either way, these are some of the upcoming changes I plan to be fiddling with. Big thanks to Ben for taking the time to help me out with the setup for the car. For now, check out Ben's 2nd morning run (which we were told at the event it was the fastest time of the day!), followed by my second and last run. Stay tuned!


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