- Aspect ratio
- The sidewall height as a percent of the section width, the second number in a size like 265/70R17.
- Backspacing
- The distance from the wheel’s mounting face to its inner edge.
- DOT code
- The tire identification number; its last four digits are the week and year of manufacture.
- Flotation size
- A size written in inches as height × width R wheel, like 33x12.50R15.
- Load index
- A number after the size that stands for the maximum load one tire can carry.
- LT
- Light truck. LT sizes, like LT285/75R16, are built for heavier loads.
- Minus sizing
- Fitting a smaller wheel and a taller-sidewall tire, often for winter tires.
- Offset
- The distance in millimetres from the wheel’s centerline to its mounting face. Positive offset sits the wheel further in.
- Overall diameter
- The full height of the tire: wheel diameter plus two sidewalls.
- P-metric
- A passenger-car size marked with P, like P265/70R17.
- Plus sizing
- Fitting a larger wheel and a lower-profile tire so the overall diameter stays close to stock.
- Revolutions per mile
- How many times the tire turns in one mile: 63,360 inches ÷ circumference.
- Section width
- The width of the tire in millimetres, sidewall to sidewall, the first number in a metric size.
- Sidewall
- The side of the tire between the tread and the wheel. Sidewall height = width × aspect ratio.
- Speed rating
- A letter after the load index for the maximum speed the tire is rated for in testing.
- ST
- Special trailer. ST tires are for trailers only.
Tire size glossary
Plain-English definitions of aspect ratio, section width, sidewall, overall diameter, plus sizing, offset, backspacing, load index and speed rating.