I also noticed a definite improvement in handling and braking with higher pressure (42/40 psi).

An interesting article on how handling, resistance to hydroplaning, and tire wear all improve with higher tire pressure is Driving Under Pressure.

A good demonstration for EVOC instructors is to have students drive a high-speed course in a vehicle with 32 to 35 psi. Then have them run the same course with 44 to 50 psi in the tires. The student will experience a marked difference in performance.

 

The tire pressure is directly related to the load on the tires. If you have more weight, then you need more pressure. if you have less weight you need less pressure. there is a standard chart that will tell you what size tire can handle what load at what pressure. This is independent of the brand of tire. Then each brand will put a maximum pressure they feel is safe for the tire on the sidewall.

The true way to determine if you have your tires inflated properly is to "paint the tread" and drive forward and see if you have a nice uniform and flat contact patch. if the center is not in contact, they are underinflated, if only the center is in contact, they are over inflated.

I personally like mine at 45 PSI.

 

Well... that's not entirely accurate. The speed of rotation will deform the tire surface as well. Going 2mph will paint a different story then going 65mph.

 

Yes, but it will get you close. We are not talking about top fuel tire that are designed to grow, but tires that are designed to stay stable as much as possible. In addition, with the stiff sidewalls on current radial tires, a severly underinflated tire can still look inflated.

 

not likely on such a tall profile tire. maybe a 45 or 55 profile tire can still remain looking inflated. but a 70? i don't think so.

 

I have a small air tank here at home. Later at night when we got the new car home, I aired each of the tires to 40 psi cold. This car steers better than any I have every owned. My car came with michlins. I'm sure it helps the mpg some. The tires seem to ride quiet and smooth even at that pressure.