I'm running 32 psi (cold) all the way around and have averaged a bit over 28mph overall over the past 800 miles. I was thinking of pumping the tires up to 40 or so and seeing what that does to mileage. So...what are y'all running?
Poor tradeoff, tires for gas. Also can a safety issue on several grounds (see Ford Explorer rollovers for example). Do not exceed the tire pressure max listed on the tire. What will work is to purchase the low rolling resistance tires coming on the market. These tires can be hard compounds so you will loose some traction in dry conditions, lots in wet conditions, and all in snow and ice conditions. Having lived 10 years in DC you really don't get any real snow or ice so that is not a problem.
With all of the legal out of the way, it is important to keep the tp up to spec for your vehicle. The gains of increasing tp are small but the losses for low pressure are great. Diminishing returns problem. Running the smallest tallest tire (real retro look) you can find will help but probably more from tire dia then anything else. You will lose ride and handling somewhat.
I think mine are at 35 cold and when hot can get up to 38. This is how I got them from the dealer and haven't changed a thing on them yet. The TPM's haven't yelled at me either, do i'm just going with it being correct.
I checked my tire pressure one day when I came out from work and the tires sitting toward the sun was 2# more in pressure. My wifes uncle told us he replaced his air w/ nitrogen and it made a huge difference, so I contimplating changing also. I know from being around racing it makes a difference.