For drivable fun, I use this setting:
(NTSC 1.2, normal tire)
Nissan Skyline GT '99 Calsonic
deep forest lap time: 1.05.xxx
Suspension
-Spring Rate: 20.0 / 20.0
-Ride Height: 65 / 65
-Bound: 10 / 10
-Rebound: 10 / 10
-Camber: 0.0 / 0.0
-Toe: 0.00 / 0.00
-Stabilizers: 1 / 1
Transmission: Default
Downforce : 0.78 / 0.99
LSD
-Initial: 1 / 1
-Acceleration: 1 / 10
-Deceleration: 1 / 1
Nissan R390 GT1 '98
deep forest lap time: 1.05.xxx
Suspension
-Spring Rate: 20.0 / 16.0
-Ride Height: 55 / 55
-Bound: 10 / 10
-Rebound: 10 / 10
-Camber: 0.0 / 0.0
-Toe: 0.00 / 0.00
-Stabilizers: 1 / 1
Transmission: Default
Downforce : 0.78 / 0.99
LSD
-Initial: 1
-Acceleration: 25
-Deceleration: 1
Toyota GT-ONE Road Version
Nissan R390 GT1 '98
deep forest lap time: 1.01.xxx
Suspension
-Spring Rate: 20.0 / 16.0
-Ride Height: 55 / 55
-Bound: 4 / 4
-Rebound: 4 / 4
-Camber: 0.0 / 0.0
-Toe: 0.00 / 0.00
-Stabilizers: 1 / 1
Transmission:
move final drive to 5.500 then move auto setting to 20
Downforce : 0.52 / 0.85
LSD
-Initial: 1
-Acceleration: 25
-Deceleration: 10