The basics of what your average...
The basics of what your average radial tire's sidewall is telling you. This is a metric measurement, except for the wheel size, since radials were first embraced in Europe because of their performance characteristics.
As the aspect ratios decreased (tires became shorter and wider), tire engineers determined that belts could be layered under the tread to provide better tread face integrity. These belts were originally constructed of rubber-permeated fiberglass mesh; we referred to them as fiberglass belts, then later steel mesh, which we refer to today as steel belts. Bias-ply tires were belted during the '60s, particularly on the lower-aspect-ratio performance tires, but for the most part we only correlate belted tires, more specifically the steel belted tire, with modern radials.
Coker goes on to tell us that bias-ply tires made today are far superior to those of yesteryear thanks to modern manufacturing and materials. And believe it or not, there are diehard bias-ply tire owners due to the fact that there isn't a radial tire that matches the look of them for restoration and period-style customs and hot rods. Our own Rob Fortier wouldn't be caught dead with radials on his '53 Chevy truck because the aesthetics of the tire are as important to its overall look as the right paint or upholstery job. The most common "big" decisions that need to be made when it comes to buying bias-ply tires are figuring out if you want a black or a whitewall tire, and if you choose the latter, how wide of a whitewall you want. Of course, Coker has just about all these bases covered for you.
If it were only that simple when it comes to choosing modern radial tires! Radial tires have more numbers and codes on their sidewalls than you can shake a tire iron at, but what do they all mean, and how do you know you are buying a "good" tire? Every tire carries a DOT (Department of Transportation) serial number (see pg. 28) and needs to meet certain requirements before it can legally be used on the highways, but what differentiates a cheap tire from the more expensive ones in a comparable size? Mostly the materials or rubber compounds they are made of. Different compounds make a tire softer or stickier, which gives it good traction but is prone to wear out quicker, where a "harder" tire could last longer but wouldn't offer the same performance characteristics when it comes to cornering, traction, and braking. There is a government rating system called UTQG, or Uniform Tire Quality Grading system, that oddly enough isn't required on all tires, just P235/75/R15 and smaller, and isn't strictly enforced for whatever reason. However, the UTQG system does help illustrate the differences in tire quality and is rated as follows: