I understand that the maximum psi located on the tire is not where you want to inflate it to and that the optimum tire pressure is located in the manual. My problem is that in my 1999 Honda Accord manual it says that the tires that should be on my car is the 89H and they should be inflated to 30 psi, but the tires I have on my car are 91H. Is my optimum tire pressure supposed to be 30 psi even though the tires are not what they are supposed to be, and if it isn‘t, then how do I find out what the correct tire pressure should be?
If the size of the tire is the same, it's 30 psi.
It's still 30 psi. The pressure on the tire is max pressure, including the pressure you will get from heat, which raises the tires air pressure.
This is because the tires originally fitted to your vehicle were built to the Passenger Metric sizing standard and are P195/65R15 89H while the replacement tires you have now were built to European Metric sizing standards (size 195/65R15 91H). Notice no P at the beginning of the size description and the different load index of 91 instead of 89. Dimensionally these tires are identical and interchangable but the way the load capacity (how much weight they can support) is figured is slightly different. At 30 psi for example the load capacity of the P195/65R15 89H is 1,190 pounds while for the 195/65R15 91H it is 1,179 pounds. This 11 pound difference in this case is not enough to get excited about so you can use the same inflation pressure without worry. Good question and a sharp eye. Most people would not have noticed the difference. ***EDIT*** Your welcome and I mean it. Very few people would have seen that difference and had enough sense to ask. It was an excellent question.
