Tire Definitions
Aspect Ratios
Truck tires sizes starting in 8, 9, 10, 11 and 12 are standard profile tubeless with the tire body width in inches. Standard profile tires have an aspect ratio of 88 percent. The height of the tire from rim to tread will be 88 percent of the width. An 11 R22.5 tire will be approxi-mately 11 inches wide and 9.5 inches high. Low profile tires show the width in millimeters and the aspect ratio. A 275/80R22.5 tire is 275 millimeters wide and 220 millimeters high (an 80% aspect ratio). Typical low aspect truck tire ratios are 70 percent, 75 percent and 80 percent. Tube-type tires are given widths as 9.00, 10.00 or 11.00, as in 1000R20, pro-nounced "ten hundred R twenty." Tires requiring inner tubes have an aspect ratio of 98 percent.
Tire Load Ranges
The final letter in the tire size is the load range, which indicates how much weight the tire can carry.
Load Range F - 12 ply -
for 17.5 tires and certain 19.5 tires
(more recent 19.5 tires are now made as 14ply)
Load Range G -14 ply -
the most common load range for 22.5, and 24.5 tire sizes
Load Range H -16 ply -
used more for higher weight applications in 22.5 and 24.5 sizes
i.e. motor homes, dump trucks, tow trucks, logging trucks
Load Range J - 18 ply -
used primarily for buses and larger RVs
Load Range L - 20 ply --
used mostly for Super-Singles, and Wide Base commercial
applications such as mobile cranes, concrete ready mix trucks,
firetrucks and heavy rescue towing trucks.
Generally speaking,
a 14 ply tire can carry 6,100 pounds of weight at 100 PSI.
a 16 ply tire can carry 6,700 pounds of weight at 105 PSI
a 18 ply tires can carry 7,100 pounds of weight at 110 PSI
a 20 ply tire can carry 12,000 pounds of weight at 120 PSI
Wheels
All wheel sizes are the wheel diameter in inches. Wheels with half-inch sizing are single piece for tubeless tires.
Common tire sizes for commercial vehicles are 19.5, 22.5 and 24.5 inches. Whole number sizes indicate multi-piece wheels that require an inner tube.
Most common tube wheel sizes are 20, 22 and 24 inches.
Truck wheels also come in several widths; a tire size chart should be consulted to match the tire size and wheel width.
A Brief History
Modern tubeless, radial commercial tires have become standard only since the late 1980s.
Before then, the most common sizes were 10.00-20 (Pronounced "Ten Hundred Twenty) and 10.00-22. (Pronounced "Ten Hundred Twenty Two) The tubeless radial equivalents of these tires are 11R22.5 and 11R24.5. The low-profile tires became common in the late 1990s on highway trucks. The low profile tires offer less weight -- meaning better fuel mileage, and are about 1" lower in height, meaning the vehicle has a lower center of gravity for better handling and control.
