Please don't spread misinformation. Ply rating was for older bias ply tires that used cotton plies as part of their construction. Today's tires use better materials and a load range rating.Ply rating is the # of plys under the tread, not the sidewall.
Here's a quote from TireBuyer.com:
These days, tire ply rating is more commonly expressed as “load range.” The days of cotton layers or plies forming the internal construction of tires are long gone, so the ply rating no longer has a direct connection to a tire’s construction and number of layers. With modern tire engineering and materials it's possible to create greater tire strength and capacity without adding layers.
Here's a quote from Tire Rack:
Today's load range/ply ratings do not count the actual number of body ply layers used to make up the tire's internal structure, but indicate an equivalent strength compared to early bias ply tires. Most radial passenger tires have one or two body plies, and light truck tires, even those with heavy-duty ratings (10-, 12- or 14-ply rated), actually have only two or three fabric plies, or one steel body ply.