After growing steadily for the past 20 years, the number of recognized diameters and aspect ratios of radial car tires available to U.S. consumers has shrunk.
According to the Tire & Rim Association (TRA), the number of diameter/aspect ratio designations fell by 21 this year, to 249, as small rim diameter, high aspect-ratio sizes are being phased out.
The decline of 21 is a net figure, derived from 27 rim diameter designations phased out and six new ones introduced, including the first 21-inch size. The TRA yearbook added one 22- and one 23-inch size last year.
The trend is most noticeable in the 13- and 14-inch categories, where the number of fitments available is down by eight and 12, respectively. At the other end of the scale, there are four new 18- and one new 20-inch sizes.
Nearly half of the sizes listed by TRA are 17-inch and greater.
Broken down by aspect ratios, the sizes disappearing are in the 50-series and higher. Gains were made in the 45-series (up three) and 40-series (up one).
Nearly half of the size designations by aspect ratio are now 55-series or lower.
Prior to this year, the number of size designations had grown more than fourfold in 20 years-to 270 from 61 in 1983.
The TRA data reflect size popularity statistics from the Rubber manufacturers Association, which show six 16- and two 17-inch sizes among the 10 most frequently mounted original equipment sizes and six 15- and one 16-inch sizes among the 10 most popular replacement market tires.
The TRA is the U.S. standardizing body for the tire, rim, valve and allied parts industry. Founded in 1903, the association said its primary purpose is to establish and promulgate interchangeability standards for tires, rims, valves and allied parts.
The TRA issues standards for tires, rims, tubes, valves and flaps for passenger cars, motorcycles, bicycles, trucks, buses, mobile homes, trailers, aircraft, earthmoving, road building, mining, logging, agricultural, industrial and other vehicles.