Originally Posted by UseTheEarth
Dealer or Factory put 28-29 PSI
Sticker on Driver Side door opening says 33 PSI
Tires say 44 PSI MAX
I just put 37 PSI in. Is that dangerous?
If not let's see if I improve from 41.3 MPG!
You will be fine
. I've had my I2 since May of 2009. I've gradually increased the tire pressure from factory to 36, 38, 40, and 41 PSI. I find that the ride and mileage is quite good at 39-40 PSI, so I keep them at that pressure.
The max sidewall is 44 PSI. This is the maximum pressure at which the factory recommends tires before bulging begins to occur. It is NOT the max pressure before explosion. Anyway, you need to take into account that the pressure inside the tire will increase due to the ideal gas law (pV = nRT). That is, the pressure times the volume is equal to two constants times the temperature. Since the volume remains the same but temperature increases due to road friction (heating up the air inside the tire), the pressure also increases to balance the equation.
That said, I'd imagine the pressure to increase a few PSI after sustained highway driving, but haven't done any calculations to quantify the amount. It won't be a huge amount though (just a few PSI), so inflating to about 40 PSI is fine.
Modern tires are steel-belted tires. You are safe to run up to the max sidewall, but take off a few PSI to allow for increased pressure due to heat. Your ride will get more bumpy, but fuel economy will increase. In fact, it is better to run the pressure higher than the factory recommended in some cases, otherwise you will see increased wear on the outer edges of the tires due to sagging in the center.