The major reason manufactures recomend a certain psi is that it gives the most comfortable ride. This is probably why certain luxury vehicles come off the lot with under inflated tires. The dealer wants to sell a car so they lower the psi.

They could compensate for the ride by improving the suspension, but if I were to build a car and I wanted to make money why would I put a lot of money into a suspension when I can just lower the recomended PSI by 5 PSI? Financialy it doesn't make sense.

BTW, hydroplaning goes down with over inflated tires, stoping distance shortens in all instances except stopping in the snow. These are things most people make wrong assumptions about.

My hydroponics experiment

You ever notice how hard it is to lip read cartoon characters?
"Crazy is what the sane call Delta Flyer"