BSCC 2018-7 10212018

Had originally planned to put the Evo away for the season, as the last event had been the track day I did on 7/7 – however, the more I had thought about it, the push that the car was experiencing had been nagging me. The car physically will tend to push due to most of the mass being on the front of the car, but the more I drove the M3, the more I wanted to figure out how to better balance the Evo. As my suspension set up was pretty loose, the next thing I wanted to look at was the differential. The Cusco 1.5-way that I had been running for a while had always felt very tight, but the more I evaluated my setup, the more I felt this was the cause of some of my understeer – particularly for turn-in, where the 1.5-way would attempt to lock the rear wheels.

I have decided to swap the rear differential from the Cusco to an OS Giken. It is the same 1.5-way, with 38/25 ramps (vs the Cusco’s 55/20), so technically on decel it should promote more understeer. However, after speaking with the OSG team, they convinced me that the negative preload springs in their differential would force the diff “open,” which is what you want when you turn-in. Before swapping in the new diff, I decided to have one last event in the old setup, so that I could pay close attention to any differences between the diffs for the next event I get.

The Evo actually felt really good the first few runs. I did make one setup change, which was that I ran the shocks softer, at 10/5 vs the usual 6/5 or 5/5. I believe this did make a difference, but in exchange the car had a lot more roll in the front, which did impact my driving the harder I pushed I ran the first few runs in Snow, then Gravel, then Tarmac, and each mode did make a difference. However, by the end of the runs, with hot tires and me driving harder, the car did start to push again. The first runs, the car would rotate beautifully on throttle lift, and by the end of the runs that was all gone. I think a lot of my push has to do with these tires, but I’m going to continue trying to optimize my setup on these.

Regarding the diff, I’m not sure how much they contributed to the understeer on throttle off, but I did notice how aggressive they tried to lock on part throttle. The sensation of the rear attempting to lock is difficult to describe, and while I wouldn’t say it caused too much understeer, there is some unnatural effect from it that I think the OSG, with milder ramp angles on acceleration, can fix. I am hoping any off throttle understeer will also be completely eliminated with the negative preload springs – otherwise, I had originally wanted to run the 1.1-way diff with almost no locking on braking.

Regarding my driving itself, I managed to find more time by slowing down less in one area of the transition, right at 25s. I also tried to carry a little more speed in the slaloms, and need to work on consistent speed in slalom vs on/off throttle. The course itself was insane, with two areas requiring 3rd gear in this car, with some very risque braking zones, and one Z06 ending up spinning off and needing a tow. Otherwise, my two fastest times had cones on them, and I really needed those runs to help me win BSCC this year, which was one of the goals. Likely it will boil down to the last event, where I may be testing out a new differential – we shall see!

Things to work on (Evo):

  • Think through runs, where I can gain time, where I need to back off
  • Smoother throttle application, even for the Evo, as I can feel the diff attempting to lock
  • Carry more speed into slaloms & maintain speed vs on/off throttle

Notes (Evo):

  • 0.5 tank
  • Camber at -3.3, -1.9 rear,  0 toe front 0 toe rear
  • 35psi all around (RT615k+)
  • ACD (Aggressive): Tarmac, Dampers 10/5 F/R, RSB on stiff
  • 2018 Runs: 33 (6 on RS4s, 30 (+7) on RT615k+)

2018 Run Count: 81 (+7 Evo)

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