i have been using this tune on mine and it seems to suit me well. There may be better tunes out there, but it seems to handle like a dream for me.
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nissan xanavi nismo z (super gt) '06:
body/chassis | aerodynamic adjustment
down-force: 40 / 65
transmission | gear ratio
top speed: 200 +/- mph (depending on track)
drive-train | lsd
initial torque: 0 / 10
acceleration sensitivity: 0 / 46
braking sensitivity: 0 / 15
suspension | suspension
ride height adjustment (mm): -9 / -7
spring rate (kgf/mm): 12.4 / 13.2
dampers (extension): 5 / 7
dampers (compression): 4 / 5
anti-roll bars: 6 / 4
suspension | wheel alignment
camber angle: 1.7 / 1.3
toe angle: -0.04 / +0.14
brakes
brake balance: 4 / 5
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most of this stuff depends on driving style. I also have all optional upgrades added, use racing soft & abs 1 only.
Good luck.