Tires: Recommended tire inflation pressure, tire placard, cooper discoverer

Question
What is the recommended tire inflation pressure for a Cooper Discoverer A/T 31X10.50 R15 LT tire?

Answer
Jim,

Recommended inflation pressures depend on a lot of things - among them are the load on the tire, the tire size, the conditions a tire will be operated in etc.  

The load on the tire is mostly about the vehicle it is on.  Any particular vehicle can accommodate a variety of tire sizes - and each size might require a different pressure.  In theory, this would make the pressure recommendation very difficult to do.  However, they've made it easy:

On every vehicle sold in the US, there is a sticker – commonly called the tire placard - that lists the original tire size and the proper pressure for that size.  The placard is usually located on a doorpost or in the glove box – but sometimes it is located in the trunk or on the fuel filler door.

BTW, it doesn't matter who makes the tire or what pressure is listed on the tire's sidewall, if the tire size is the same as the placard, then the pressure listed on placard is also appropriate.

One word of caution:  Some trucks use tires with the letters "LT" in front of the tire size - and some trucks use tires with the letter "P" in front of the tire size - and some trucks use tires with the letter "C" after the tire size.  You should not use "P"'s in place of "LT"'s and vice versa.

Tires where the letter “C” is behind the tire size require special care to insure that the proper tire is used.  These tires are built to a European style tire sizing system.  They are equivalent to “LT” sizing and “LT” tires can be used in their place – although you generally will not find an equivalent.  Consult a tire dealer and be sure you point out the “C” behind the size.

You should be sure the pressure on the sidewall equals or exceeds that pressure on the placard.  If you do this the issue about the letter "C" in the sidewall will take care of itself (which is not true with "LT"'s vs "P"'s.)

If you are using a tire size that is different than what is listed on the placard, then the pressure has to be recalculated.  The calculation is not difficult, but it requires tire load tables which are not allowed to be published in the Internet because of copywrite laws.  However, I have a copy and would be glad to do the calculation, but the starting point is the vehicle placard: Tire size and inflation pressure.  I will also need to know the new tire size.