Tires: Load Range Change, light truck applications, inflation pressure

Question

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The text above is a follow-up to ...

-----Question-----
I have a Silverado 1500 with the 265/75/16 load range C tires.  I was wondering what kind of tire life and ride quality would I get if the truck's tires were switched to load range D or E?  Will the extra capacity in the tire equal to a longer tire life or would I just be wasting my money for something that my truck does not need?
-----Answer-----
Woody,

There is a concern here that we need to clear up first - and that is the load carrying capacity of the Load Range C tires.

There are several versions of Silverados and they have different tires (and different load carrying capacities).  But the tire that originally came on the vehicle will be listed on a label - commonly called the placard - which on GM trucks, if I remember correctly, is located on the driver's door.  The inflation pressure will be listed there as well.

Would you please check that and respond back with both the original tire size and the inflation pressure?  Be sure to include the letters that are there, like "LT" or "P".  Those letters change the way the tire is designed, particularly regarding load carrying capacity.  It's that change that has me concerned.

The tire size as listed on the door label is p265/75R16.  The inflation pressure is 35psi and the speed rating is an S.  I like the LT rated tires because they seemed to handle towing and hauling better than the P rated tires.  The P rated tires had a lot of sidewall flexing that translated into a squish ride.  

Answer
Woody,

I was afraid of that!!!

A P265/75R16 has a maximum load carrying capacity of 2601 # at 35 psi.  However, for Light Truck applications, P metric tires are supposed to be derated 10%.  That means the load carrying capacity is reduced to 2341 #.

An LT265/75R16 Load Range C has a load carrying capacity of 2470 # at 50 psi.  This means that you should be running 50 psi.

I know what you are thinking...."It's the same size!"

Actually, no, it isn't.  LT tires are the little brothers of the over the road truck tires - you know, the 18 wheeler stuff.  

So an LT tire gets it's longevity from the increased inflation pressure.  Plus all the tire manufacturers do their durability test at these load and pressures.  

What I am trying to say is that there is a certain risk associated with using 35 psi.  Sure the risk is low, but I want you to be aware that it is there because sometimes that results are tragic.

OK, enough of the melodramatic!!

Let me now answer your question.

For practical purposes, going from a Load Range C to a D or an E is just a matter of gaining the ability to use more inflation pressure so you can carry more load.  If you don't use more inflation pressure, you won't experience any improvment in tread life.

But using more inflation pressure does improve tread wear and tire durability.  So if you want this type of improvement - more pressure.