Hello, I’ve been enjoying reading your blog for several weeks now and wanted to add a bit on truck tire ratings from the perspective of somebody who used to own a small tire shop in truck country (rural Alaska). The whole thing with rating a tire by the number of plies dates back to the days of bias ply tires when the tires actually were load rated according to the number of plies. That system has been obsolete for years with the advent of radial tires, which are not constructed the same way to achieve the same strength. The letter load ranges are usually equated with the old ply ratings by tire salesmen (i.e. “C” equals a “6” ply rating, etc.) in order to explain the load ratings in terms that their customers will be familiar with.
Nearly all radial tires have 4 plies in the tread area, and 2 plies in the sidewall, no matter what their load rating. The heavier duty tires will have thicker and stronger plies in the higher load ratings, although the number of plies will generally remain the same. A few tires specifically designed for off road use will have a 3rd sidewall ply for extra reinforcement against rock cuts; the two that I am aware of are the BF Goodrich Mud Terrain, and the Goodyear Wrangler MT-R. My brother and I run MT-Rs on our Jeeps and have no complaints about them.- Del R.
Letter Re: Six Versus Eight Plies for SUV and Light Truck Tires
