Originally Posted by HellFire

I am of the mind that the speed needs to be taken into consideration when making the factory recommendations. As are the tire experts evidently. Most of us are going to be fine at that. However, it has been my understanding that performance tires need to be tuned to their speed. The manufaturers are recommending pressures for average speeds and general purposes. Increasing tire deflection by using a lower pressure than the tire can handle improves ride quality by allowing the tire to flex when it encounters irregularities in the road. With that said, the flex of the tire also heats up the tire. Just like bending a piece of metal repeatedly heats it up, rubber is no different. The more you flex the metal, the hotter and more fragile it becomes. Tires are no different(albeit not nearly as extreme with the strength loss and heat production because it was designed to flex easily). At speeds 3 times the average driving speed, it is going to flex even more than 3x because of additional force and friction at speeds etc. My car came to me with 42 lbs of pressure in each tire and I drove it that way for a few thousand miles myself. It will ride like a go-kart and rattle your teath, but it has not worn my tires unevenly at that pressure(mostly 80 MPH highway). Remember this is a wide tire and a wider radial tire typically needs more pressure to keep that center from bulging in anyway. Also the pressure on the sidewalls from air is always the same as that on the treads. Centrifugal force tugging on the center of the treads however is increased dramatically as speeds increase. The higher the overall air pressure is, the less centrifugal force place a part on tire deformation. After all, the ratio of pressure left and right on the sidewalls vs up and down on the treads is the same at low speeds or 0mph. As speed increases, the ratio of pressure on the treads vs the sidewalls increases. So, to keep this simple, I think of it as 3 main factors contolling deflection. Side pressure, outer pressure and centrifugal force. We cannot remove the centrifugal force without going slower and we cannot change either of the other two forces by themselves, so(at speed) our only option is to increase BOTH of the forces we can alter(by increasing air pressure), which lowers the % ratio centrifugal force plays in tire deformation. The chalk method works great for in town driving, but the tire acts differently at high speeds because of the other force not in play at low speed.
Please keep in mind that this is all my understanding and I am no expert. With that said however, there are only two things that affect my oppinion on anything. My own mind and the mind of experts in the field. The experts in tires can probably teach me a LOT about tires(and probably show me some errors in my above logic LOL). Much more so than the sticker on the door. Experts put that sticker on the door for a reason, but the average person doesn't know why they came to that number, when the tire can take both more and less pressure. So, if I am gonna drive my car in excess of the speeds for the area the car is sold in, I'm gonna trust my own understanding until I can find an expert. At that point, I must yield to their knowledge. So, why are we fighting the experts all the time? LOL I am guilty of it too, but I am being silly when I do. JMO