Tire size decoder
Type a size from the sidewall. Works for semi-truck, farm, OTR (loader, grader, dump truck), skid steer and forklift tires.
How tire sizes are written
Metric — 295/75R22.5: section width in mm / aspect ratio (sidewall height as % of width), construction (R = radial, B = belted bias, - or D = bias), rim diameter in inches. Overall diameter follows from the numbers.
Inch width — 11R22.5, 18.4-38, 23.5-25: nominal section width in inches, construction, rim diameter. The aspect ratio is not in the name, so the exact diameter comes from the manufacturer's data book.
Low section — 11L-15: the L means a lower sidewall than a standard size of the same width; common on implements.
Flotation — 31x10.50R15: overall diameter × section width, both in inches, then rim.
Press-on (forklift cushion) — 21x7x15: overall diameter × width × inside (band) diameter, in inches.
Prefixes: IF / VF on farm tires = Increased / Very High Flexion (more load at the same pressure, or the same load at lower pressure); LT = light truck; ST = special trailer.
Load index and speed symbol (e.g. 146/143L) follow the size: two load indexes on truck tires = single / dual mounting; L = 120 km/h (75 mph).