I wouldn't even get close to 40 PSI if I were you. The tires microbounce and don't really make contact with the road. The handling will be crap. Even with new suspension over inflating the tires prevents the tires from maintaining contact with the road. They microboumce and chatter over every little crack. You send shockwaves through the shocks cavitate the oil and just beat up the car without having real traction. It doesn't really affect your feel economy anyway and just destroys the ride. In the suspension world we have a saying: stiff shocks soft tires.
Looking at the video posted in post #40, that is exactly the wear pattern I've seen myself when trying higher pressures. Does the tire look inflated like a balloon? No, it is perfectly flat, right? If you look at the first section of tread from the middle and outside regions of the tires you can two if not three millimeters of the tread at the first section of tread from the middle and, on the outside, it looks like it never has even contacted the pavement ever. One other observation is that tire would not have been legal for quite some time after the middle of the tire wore to 1.6 mm (1/16") and for me, it would take a year and a half to wear away that amount of rubber. On this tire, it might have been only a third to a half of that time given only the middle of the tire (as evidenced) has any real contact with the pavement.
When I was putting 42 PSI in the front and 40 PSI in the rear, I had a flat tire from a sharp stone. I think the tires at these pressures are too hard. Some folks here suggest 42/40 PSI with an aim to get a higher gas mileage per gallon. Ever since I had a flat tire, I am sticking to 35 PSI as stated on the door. I do think 35 PSI gives tires more flexibility than 42/40 PSI, make tires less prone to flats, and gives you less bumpy ride.
