I need some help guys. I have a 1999 355F1 Spider. It is running 18 inch HREs with Michelin Pilot 225 45 18s on the front and 265 35 18s on the rear. I took it out of the garage for a drive and the tire pressures were around 35psi. The tires have a max pressure rating of 51psi. I inflated them to 48 psi and the car feels a little out of control, like it slides a little. Doesn't feel confident. My question is, What is optimal? Any experience? Thanks fellas.