I'd like to address a part of the post by homer's van: "Too much pressure also can cause premature center wear, but I don't know the break point." My experience with this issue is that it is a non-issue: it is almost impossible to stretch the belt unevenly on a modern, belted radial, as one would have to do in order to apply uneven pressure to the tread area, thereby wearing the center of the tread more than the edges. Uneven tread wear, as a result of over-inflation, was a phenomenon in the bias-ply and early, fabric-belted radials days. I believe that is is possible to run the tires at the maximum rated pressure (usually 44+ psi) without uneven wear...if you can stand the harsh ride. UNDER-inflation, however, WILL cause tread wear similar to what we used to see in the old days: premature wear on the edge areas of the tires. But this doesn't happen so much because of uneven pressure on the tread surface (again, the belts on modern tires remain basically, diametrically stable until the inflation pressure falls into the danger zone), but because the tread surface "rolls" under with increased slip angle, transferring load to the edge area and even up, into the sidewall in sufficiently severe cases. Under-inflation is ALWAYS the bogeyman to be avoided. Over-inflation will effect ride and handling (handling, especially when pressures are significantly higher on one end of the vehicle than the other), but is a rather "safe" condition, at least until one does the old "inflate it by eye", like the old bias-ply days, and gets the pressure WAY up...like over 45 - 50 psi.