[Hauki]

*warning - long post!*

Once aftermarket wheels/tyres go on, the door jam sticker is as much use as a one-legged man at an arse-kicking party.

But even with stock tyres on I would be inclined to run at max psi or as near to max as you deem comfortable.

Wiki'd:
"Should a low pressure tire be forced to perform an evasive maneuver, the tire wall will be more pliable than had it been of a higher pressure, and thus it will "roll" under the wheel. This increases the entire roll movement of the car, and diminishes tire contact area on the negative side of the vector. Thus only half the tire is in contact with the road, and the tire may deform to such an extent that the side wall on the positive vector side becomes in contact with the road. The probability of failing in the emergency maneuver is thus increased.

Further, with low tire pressure—due to the side wall being more pliable—the tire will absorb more of the irregular forces from normal driving, and with this constant bending of the side wall as it absorbs the contours of the road, it heats up the tire wall to possibly dangerous temperatures, as well as degrades the steel wire reinforcement; this often leads to side wall blow-outs. In an extreme case of this phenomenon, the vehicle may drive into a pot-hole, or a hard elevation in the road. Due to the low tire pressure, the side wall at the contact area will temporarily collapse, thereby wedging the tire between the wheel and road, resulting in a tire laceration and blow-out, as well as a damaged wheel.

High tire pressures are more inclined to keep its shape during any encounter, and will thus transmit the forces of the road to the suspension, rather than being damaged itself. This allows for an increased reaction speed, and "feel" the driver perceives of the road. Modern tire designs allow for minimal tire contact surface deformity during high pressures, and as a result the traditional wear on the center of the tire due to reasonably high pressures is only known to very old or poorly designed tires."

My opinion on this is,
Bridgestone, Dunlop, Pirelli etc spend a damn sight longer testing tyres tolerances and flex at varying pressures than the car manufacturer. So if the sidewall says it is safe up to 50PSI, then you can be damn sure it is safe up to 50PSI. They will have pressure tested these in multiple different temperatures, humidty & conditions. Max pressure means exactly that, the max pressure the tyre can go to whilst retaining all its design characteristics and effectiveness. IT IS NOT the max pressure the tyre will inflate too, you will probably get 100PSI into a standard tyre!

IMHO, max sidewall pressure is optimum pressure. To think your cars handling is going to be dangerous inflating your tyres above the pressure stated on the door jam sticker is quite frankly, ludicrous. As stated, this is designed more for comfort than anything else. And I would suspect in some auto manufacturers, this is to hide a multitude of sins in the cars chassis/suspension so it is purposeful set to 32 or whatever to hide these flaws.