mkirsch wrote:
valhalla360 wrote:
The ABCD... is an old system based on how many nylon plies the tire is made from...
I'd have to go back and look to verify, but I don't think that the OEM 245/75R16 tires off Dad's 1989 Chevy C2500 Scottsdale have an LT designation or an ABCDE load range rating. They just say "10 ply rating."
So ply rating was how it started. Then at some point in the 80's or 90's they must have adopted the LT-ABCDE system. Later on they started this load index/speed rating deal. Now pickup truck tires have ALL THREE which makes it confusing. IF you're not up on the legacy nomenclature you and the customer are talking two different languages.
Here's a copy of a page from the 1970 Tire and Rim Association Yearbook that has Load Range and Not Ply Rating:
Barry's Tire Tech: 1970 TRA, page 2-04The TRA yearbook from 1960 still uses PR, so somewhere in the 1960's is when they started using Load Ranges.
And according to Tire Guides, your 1989 C2500 will show an LT245/75R16 Load Range C or D and it had Load Range on the placard and the tire. Nowadays, you can only get Load Range E's in an LT245/75R16, but that's OK because the load carrying capacity of a Load Range E at the same pressure as a LR C or D is the same.
