Tires: tire pressure, bf goodrich mud terrains, tire placard

Question
QUESTION: what psi level should i inflate 255/85/R16 bf goodrich mud terrains tires on my 2001 chevy silverado 1500 4x4 ext cab short bed?

ANSWER: Ryan,

Here is my standard response to inflation pressure questions:

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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 I am not a fan of the reverse.

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 copyright 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.

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Ordinarily, I would look up your vehicle in a book called Tire Guides, that summarizes the vehicle tire placard information for US sold vehicles.  But trucks and vans come in so many configurations and the placard tire sizes and pressure vary with them, that I ALWAYS ask folks to look at the placard.  It is the only true way I can be sure the info is correct.  Needless to say, I will look up that info in Tire Guides to see if it makes sense.

So what does your vehicle placard say for tires size and pressure?

---------- FOLLOW-UP ----------

QUESTION: hey, thanks for your response.  the placard on the door recommends 265/75R16 with rims 16x7/6.5J  at 35psi cold,  which i had on previously.

the tires i put on are BF Mud Terrains T/A with specs of LT 255/85R16  119/116 Q M+S  max load 65psi cold.  same rims.  these tires fit with no rubbing and no lift on the truck body or suspension.

the placard on the door does not specify LT or P or C.

need to know what psi to set these mud terrains at for maximum performance everyday road driving.  thanks

i don't have an owner's manual that might have recommended pressures for alternate tire sizes.

Answer
Ryan,

My experience says that all GM trucks have a "P" or an "LT" in front of the tire size on the placard.  Nevertheless, it's obvious the original tire was a "P".

The load carrying capacity of a P265/75R16 at 35 psi is 2601 # - and since this is a truck application, the load carrying capacity has to be derated 10% to 2365#.

In order to carry the same load, an LT255/85R16 needs to use 47 psi - and that's why I am not a fan of replacing P metric tires with LT's.