I see this from a different perspective to all of you. I pump my tires (700x28) to about 120 psi and over a period of about a month or two they slowly go down to about 90 psi. If I let them get lower than that there is a risk of rim damage if I hit a pot hole or manhole cover with an edge. Now - if I only pump them to 90 psi I would have to re-inflate them every week at least. So it seems to me the maximum pressure is all about how long you want between re-inflation. On the other hand, the minimum pressure is all about how good the roads are. You could get home on 40 psi if the pavement is quite good and you ride carefully.