When you get up to 18,19 and above diameter wheels with short tire sidewalls, you need more pressure. It doesn't take much deflection to take out the edge of the wheel rim that has a tire with low air. Stiffness is your friend and your wallet will thank you. On front wheel drive cars, with normally about 60% of their weight on the front tires, I normally run about +4 lbs on the front and +2 on the rear. This will also improve your steering response slightly due to less tire deflection on turn in.