Can anyone please advise as to what the tyre pressure should be for 18" RS8's with a 225/40/18 tyre on them, i was recommended that the pressure be 30PSI but when parking the car (half on kerb and half off) the side of the car that's on road the tyres look like they're flat, is this purely because of the weight of the car or because the tyre pressure is too low?? Any advice would be welcomed, thanks...