I just realised the importance of a good setup on this game. It's unbelievable, the difference you can get from setting up your car properly is insane. I shaved 6 seconds of my lap time round Laguna Seca with this setup

So this is the setup I'm currently using for my Nissan 350 Fairlady. Its power is 478kW weighing 1151kg and is RWD, so no drivetrain change.
Tire Pressure Front = 2.07 bar
Rear = 2.07 bar
Gearing Final drive = 4.11
Alignment Camber Front = -0.5
Rear = -0.5
Toe Front = 0.0
Rear = 0.0
Front caster = 5.0
Anti-Roll bars Front = 6.57
Rear = 4.30
Springs Stiffness Front = 111.88 kgf/mm
Rear = 74.66 kgf/mm
Ride Height (this varies hugely between cars, so adjust accordingly with everything else) Front = 8.9 cm
Rear = 8.9 cm
Damping Rebound Stiffness Front = 13.0
Rear = 8.7
Bump Stiffness Front = 6.5
Rear = 4.3
Aero Front = Default
Rear = Default
Braking Balance = 50% front
Pressure = 100%
Differential (rear) Acceleration = 80%
Deceleration = 63%