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Tires/Old OEM 6 Ply vs. New 10 Ply inflation...

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Question
Hi Mr. Smith,

I bought a used '83 Chevy Suburban, 4WD, 3/4 Ton, Silverado trim level. I'm fixing it up —new motor , tranny overhaul, transfer case, tires, etc...

The previous owner lifted the truck 3-4 inches.  He installed expensive LT305/70/R16 mudder tires on the truck.  I hate all this — tires drift on paved roads, whole rig seemed juvenile and dangerous to me.  Sidewalls were bulging out of the wheel too.  I use 4WD ONLY because I live in the middle of nowhere and we do get stuck sometimes out here.  My house is miles from the nearest paved road.  In any case, I decided to return to "bone stock".

I had the tire size specified by GM installed at a local dealer:  LT235/85/R16.  The tire dealer recommends 55-60 psi inflation.  The tire placard does not.  It specifies a lower inflation — in the 40's, depending upon load and so forth.  I asked the boss at the tire dealer about this and he said "they", (General Motors) probably specified a tire with fewer plys, so I should choose higher inflation of 55.  Max inflation for the new tire is 80 psi.

The OEM tire was a 6 ply tire.  The new ones are 10 ply.

Is the guy at the tire store right?

Also, I'm knocking out the lift kit and using some frnt. springs from a 70 Suburban to level it all out to factory stance.  Anything I ought to know about how tire will impact this?

Thanks in advance for your help!

Paul

Answer
Paul,

First, please check your vehicle tire placard again.  Tire Guides says the placard should say 44 psi front / 80 psi rear.

Assuming this is correct (and it makes sense to me), then the vehicle originally came with Load Range E tires (10 Ply Rating).

But this doesn't answer your question - except that the question is now moot.  The load carrying characteristics of a tire is the same regardless of the Load Range (Ply Rating).  In the question you posed, the Load Range E tire would be inflated to the same as the Load Range C.  

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Barry Smith

Expertise

I have over 30 years experience in the design, manufacturing, and testing of tires. I have served as the technical advisor to the "800" number. I have authored or co-authored many publications - usually without credit. I can answer almost any technical question, but please don`t ask me to compare brands. I probably have prejudices because of my work experience.

Experience

Member SAE (Society of Automotive Engineers) Member Tire Society (Tire Technical Organization) SCCA Regional Competiton License holder Authored many training manuals on tires, their care and use.

Organizations
SAE (Society of Automotive Engineers) SCCA (Sports Car Club of America) Tire Society

Publications
You may want to visit my web site: http://www.barrystiretech.com/index.html

Education/Credentials
I am a graduate of the University of Dayton, Dayton, OH - BME, 1971 I attended graduate school at the University of Akron - but did not complete my PhD - something I regret.

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