[RedDevil]

The relation between tire pressure and rolling resistance has been thoroughly investigated in this thread: http://ecomodder.com/forum/showthrea...tire-2721.html

Audi advices the tire pressure it feels gets its cars sold best. Which usually means compromising handling and grip for 'comfort'. If economy were their sole concern the figures would be double what they are now.

Honda does that too. My Insight needs 8 PSI on top of the OEM pressure to get rid of sidewind sensibility and other nasties. Road noise increased a bit, but so did cornering speed and general car control. I feel so much safer now.

One consideration to make is the max tire pressure as stated on the tire sidewall. The tire was designed to handle that pressure, but not above.

When you raise the pressure on used tires do it gradually, especially if you are not certain that the tire has never been damaged before.
Check the tires for deformation immediately after airing up and again after some use.
Hitting a kerb or a pothole with a soft tire can damage the carcass; riding a flat tire on the rim does that too. Those tires may blow when you raise the pressure; ironically, it was low pressure, not high pressure, that did the initial damage.
They would fail in the long run even at low pressure.