Quote:
Originally Posted by ksa8907
The pressure rating on the side of the tire is more to do with what type of car the tire is going to go on rather than anything different with the tire construction. Different sizes of the same model tire will have different ratings.
High mileage tires will almost always be "aa-a" or "a-b" tires because of the tread compound.
My opinion? Of the 4 cars i have increased tire pressure on, i never kept them above 45 psi cold. The impact on fuel economy and treadwear is minimal above 38 psi.
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There are parts of this post which are right on, but there are parts that aren't.
First, the max pressure listed on the sidewall of a tire is not a rating. It is merely a statement about what the max usage pressure for that tire is. Kind of an advisory not to exceed that value.
The max pressure listed on the sidewall is not directly connected to the construction, except to say that the speed rating test requires certain pressures to be run, so the tire will reflect that and because higher speed rating require cap plies, there is a loose correlation. For example, V and higher speed rated tires are tested at 51 psi, so they will say 51 psi max, and in order to pass the test, a V speed rated tire generally needs 2 cap plies. However, there are some T rated tires with a max of 51 psi, and T speed rated tires are tested at 35 psi and don't require a cap ply to pass the test.
Tire models tend to have the same UTQG ratings and max pressures regardless of tire size, but there are some exceptions. For example, some lines of tires are original equipment lines and each tire is designed to the specs for the car it is being supplied to - and no 2 specs are the same.
High mileage tires tend not to be high temperature rating tires (that is high speed rated). You won't see many 600 and higher rated tires with AA temperature ratings.
And one last comment. If you ask the tire manufacturers for a pressure recommendation, they will point to the vehicle placard, regardless of the tire line. Put another way, what is written on the sidewall of a tire does not affect what a tire manufacturer recommends for usage pressure.