Tires: Air pressure, gmc classic, inflation pressure

Question
QUESTION: I need to know what tire pressure to run in my tires.
I have a 2007 GMC classic 3500 dually

The door sticker says LT 215/85R16 E
70 psi in the front
65 psi in the rear

The tires on the truck are LT 225/75R E

Do I use the tire pressure rated on the door?
Did GM ever put 17” tires on a 2007?
It has factory wheels, I am the second owner so I do not know if the wheels or tires were ever changed as the truck has 40,000 miles.

Thanks for your time,
Mark

ANSWER: Mark,

From a load carrying capacity point of view, an LT225/75R16 is equivalent to an LT215/85R16, so you would use the pressure listed in the vehicle tire placard.

However, you may have another problem.  The dual spacing for LT215/85R16 is 9.9" where an LT225/75R16 requires 10.2".  I know that doesn't sound like a lot, but if the duals "kiss", you might get a failure - very bad.  So you need to check this.

GM did NOT put 17" tires on 2007 Classic 2500 or 3500's  (old body style).  17" were optional on the new body style only in 2007.

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

QUESTION: Sorry I left out one important thing. the current tires on the truck are 17" wheels. I do tow a 5th wheel, with the truck setting empty there looks to be plenty room between the rear tires.

Thanks for your time,
Mark

Answer
Mar,

That was indeed an important bit of information.

While the 17" tires have an ever so slightly higher load carrying capacity, and therefore could use a slightly lower inflation pressure in order to carry the same load, it is only a psi or 2.

But there is a school of thought that says that if you have enough load carrying capacity, it is better to match the original inflation pressure so the suspension reacts as intended - and that's where I would go.

And the fifth wheel thing:  You need to check to see if you are towing within the capability of the truck.  If you are, then the vehicle tire placard is appropriate.  If not, you need a bigger truck.

So