Hi All,
This tire pressure thing has been an ongoing debate between the AAA and Cleanmpg. Wayne Gerdes pointed out that Police driving instructors recommend setting the pressure at cold max sidewall pressure, as whitevette recommends. He references a police driving training website,
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Michelin has an article which has been on some tire store websites, that demonstrates that higher tire pressures are superior for aqua-planing resistance.
And of course the more the side-wall flex, the more its going to heat up and the more its gong disipate rolling resistance. Just take a piece of stiff rubber tubing and flex it 45 degrees 20 times, feel the temp at the flex point, then do it again at 90 degrees, warmer. And one of the conclusions of the Explorer tire blow-out roll overs was that the placard pressure - 28 PSI (Yikes!) was too low for safe operation of the tires.
Most of the hypermilers in Prius' are running 42/40 at least, and some are up around 50 psi. I run 44/42 right now, and am closing in on a 68 mpg tank (at 68.6 right now, 550 miles into the tank). 44 PSI is the sidewall rating of the Michelin Hydroedge tires on my car.