Commercial Truck and Bus Tire Sizes: Common Sizes and Their Dimensions

A commercial truck or bus tire size such as 295/75R22.5 describes three things: the nominal section width in millimetres (295 mm), the aspect ratio, which is sidewall height as a percentage of width (75%), and the rim diameter in inches (22.5 in). The R means radial construction. From these numbers you can calculate sidewall height, overall diameter and circumference. Other figures on the sidewall, such as 146/143L, are not dimensions. They are performance ratings for load capacity and speed. Inch-based sizes such as 11R22.5 have no aspect ratio in the marking, so their overall diameter must be taken from the manufacturer's data.

How do you read the numbers on a truck or bus tire sidewall?

Read a commercial tire size marking from left to right. Width comes first, then the profile (if shown), then the construction letter, then the rim diameter. After the size come the load index and speed symbol. The size designation tells you the tire's geometry. The service description tells you what the tire is rated to carry and how fast it may run.

1. Find the size designation. It is the largest group of numbers, for example 295/75R22.5, 11R22.5 or 445/50R22.5.
2. Identify the width. A three-digit number (295) is the section width in millimetres. A one- or two-digit number (11) is a nominal width in inches.
3. Check for an aspect ratio. A number after the slash (75) is the sidewall height as a percentage of the section width. If there is no slash, the size uses the older numeric format.
4. Read the construction letter. R means radial. A dash, as in 10.00-20, indicates bias construction.
5. Read the rim diameter. The last number of the size (22.5, 24.5, 19.5, 20) is the wheel diameter in inches that the tire is designed to fit.
6. Read the service description. Figures such as 146/143L give the load index for single and dual mounting, followed by the speed symbol.

Metric size designations (for example 295/75R22.5)

A metric commercial tire size gives the section width in millimetres and the aspect ratio as a percentage. In 295/75R22.5, the tire is nominally 295 mm wide. The sidewall is nominally 75% of 295 mm, which is 221.25 mm. The tire mounts on a 22.5-inch rim. Because both width and ratio are stated, you can calculate the nominal overall diameter directly from the marking. Metric sizes dominate in Europe and are also widely used in North America.

Numeric (inch) size designations (for example 11R22.5 and 11R24.5)

A numeric commercial tire size such as 11R22.5 gives a nominal section width of 11 inches, radial construction and a 22.5-inch rim diameter. It does not state an aspect ratio. Sizes in this format have a taller profile than most modern metric low-profile sizes, but you cannot calculate their exact overall diameter from the marking alone. In manufacturers' published data, 11R22.5 tires are typically a little over 41 inches in overall diameter, and 11R24.5 tires about 43 inches. The exact figure varies by brand and tread pattern.

Wide-base single sizes (for example 445/50R22.5)

A wide-base single tire uses the same metric format but with a very large width and a low aspect ratio. Sizes such as 445/50R22.5 and 455/55R22.5 are designed to replace a pair of dual tires on one axle end. The marking is read exactly like any metric size. The practical difference is that one tire carries the load that two tires carried before, which affects wheel choice, offset and load rating.

Older tube-type sizes (for example 11.00R20 and 10.00-20)

Sizes with a decimal width and a whole-number rim diameter, such as 11.00R20 or 10.00-20, are older designations. They are often associated with tube-type tires on multi-piece rims. The first number is a nominal width in inches, and the last number is the rim diameter in inches. The half-inch rim diameters used on most modern truck and bus tires (19.5, 22.5 and 24.5) belong to the 15° drop-centre tubeless rim system. A 22.5-inch tire and a 20-inch tire are therefore not interchangeable on the same wheel.

Which sidewall markings are dimensions and which are performance ratings?

Only the size designation describes the tire's dimensions. Load index, speed symbol, load range and ply rating describe what the tire can do, not how big it is. Two tires of the same size can carry very different loads. The table below separates the main types of marking on a commercial tire sidewall.

Marking	Example	Type	Plain-language meaning
Section width	295 or 11	Dimension (mm or in)	Nominal width of the inflated tire from sidewall to sidewall, excluding raised lettering
Aspect ratio	/75	Ratio (%)	Sidewall height as a percentage of section width; a lower number means a lower profile
Construction	R	Construction code	Radial construction; a dash indicates bias
Rim diameter	22.5	Dimension (in)	Diameter of the wheel the tire is designed to fit
Load index	146/143	Performance rating	Coded maximum load per tire: first figure for single mounting, second for dual mounting (146 = 3,000 kg; 143 = 2,725 kg)
Speed symbol	L	Performance rating	Coded maximum speed at the rated load (J = 100 km/h, K = 110 km/h, L = 120 km/h, M = 130 km/h)
Load range / ply rating	Load Range G (14 PR), H (16 PR)	Performance rating	North American strength classification linked to maximum load and inflation; not an actual count of plies
Maximum load and pressure	Max load single/dual at stated kPa or psi	Performance rating	Highest permitted load and the cold inflation pressure at which that load applies
Tubeless	TL or TUBELESS	Construction	Tire is designed to be used without an inner tube
Winter and traction markings	M+S, 3PMSF symbol	Use marking	Mud and snow designation; the three-peak mountain snowflake indicates a tire that has passed a snow traction test
Regrooving and retreading	REGROOVABLE, RETREADABLE	Use marking	Tire casing is designed to be regrooved or retreaded
DOT date code	2324	Production data	Week and year of manufacture (week 23 of 2024)

The load index is the figure most often confused with size. In 295/75R22.5 146/143L, the numbers 146 and 143 have nothing to do with width or diameter. They indicate that the tire may carry up to 3,000 kg when mounted as a single and up to 2,725 kg per tire when mounted as a dual. These limits apply only at the inflation pressure specified for that load.

How do you calculate sidewall height, overall diameter and circumference?

For a metric tire size, the nominal overall diameter equals the rim diameter plus two sidewall heights. Sidewall height is section width multiplied by the aspect ratio. Because the rim is measured in inches and the width in millimetres, convert one unit first. One inch equals 25.4 mm.

1. Calculate sidewall height: section width (mm) × aspect ratio ÷ 100.
2. Convert the rim diameter to millimetres: rim diameter (in) × 25.4.
3. Calculate overall diameter: rim diameter (mm) + 2 × sidewall height (mm).
4. Calculate circumference: overall diameter × π (about 3.1416).
5. Optional – revolutions per distance: 1,000,000 mm ÷ circumference gives revolutions per kilometre; 1,609,344 mm ÷ circumference gives revolutions per mile.

Worked example for 295/75R22.5:

• Sidewall height: 295 × 0.75 = 221.25 mm
• Rim diameter: 22.5 × 25.4 = 571.5 mm
• Overall diameter: 571.5 + (2 × 221.25) = 1,014 mm, which is about 39.9 in
• Circumference: 1,014 × 3.1416 ≈ 3,186 mm, or about 3.19 m
• Calculated revolutions: about 314 per kilometre, or about 505 per mile

These are nominal figures for an unloaded tire. They do not account for tread design, rim width, load or wear. Manufacturers publish measured revolutions per mile or per kilometre for each tire. Those published figures are usually somewhat higher than the simple calculation, because a loaded tire rolls on a smaller effective radius.

What are the standard tire sizes for trucks and buses?

There is no single standard truck tire size. Instead, size designations are standardised by tire and rim organisations such as ETRTO in Europe and the Tire and Rim Association in North America. A relatively small group of sizes covers most heavy truck, trailer and bus applications. The ten sizes below are frequently encountered on line-haul, regional, trailer and bus vehicles. They are listed by type, not ranked by sales, because their popularity differs by region and application.

10 common commercial tire sizes and their calculated dimensions

Size	Typical use	Sidewall height (calc.)	Overall diameter (calc.)	Circumference (calc.)	Revolutions per km (calc.)
295/75R22.5	Tractors and trailers, especially in North America	221.3 mm	1,014 mm (39.9 in)	3.19 m	314
11R22.5	Tractors and trailers, especially in North America	Not calculable from the marking	Manufacturer data, typically a little over 41 in	Manufacturer data	Manufacturer data
11R24.5	Tractors and trailers on 24.5-inch wheels, North America	Not calculable from the marking	Manufacturer data, typically about 43 in	Manufacturer data	Manufacturer data
285/75R24.5	Low-profile size on 24.5-inch wheels, North America	213.8 mm	1,050 mm (41.3 in)	3.30 m	303
315/80R22.5	Trucks, coaches and construction vehicles, especially in Europe	252 mm	1,076 mm (42.3 in)	3.38 m	296
295/80R22.5	Trucks and coaches, especially in Europe	236 mm	1,044 mm (41.1 in)	3.28 m	305
315/70R22.5	Tractor steer and drive axles, especially in Europe	220.5 mm	1,013 mm (39.9 in)	3.18 m	314
385/65R22.5	Trailer axles and heavy steer axles, especially in Europe	250.3 mm	1,072 mm (42.2 in)	3.37 m	297
445/50R22.5	Wide-base single replacing duals on drive or trailer axles	222.5 mm	1,017 mm (40.0 in)	3.19 m	313
275/70R22.5	City buses and regional vehicles	192.5 mm	957 mm (37.7 in)	3.00 m	333

Medium-duty trucks and smaller buses often use 19.5-inch wheels. By the same method, 225/70R19.5 calculates to about 810 mm (31.9 in) overall diameter, and 245/70R19.5 to about 838 mm (33.0 in). All values in the table are nominal geometry rounded for readability. They are not measured dimensions of any particular tire model.

How do width, aspect ratio and rim diameter change tire dimensions?

Each part of a metric size affects overall diameter in a different way. Width matters only through the sidewall, because sidewall height is a percentage of width. Aspect ratio changes sidewall height directly. Rim diameter adds to overall diameter one-for-one. Every millimetre of overall diameter adds about 3.14 mm of circumference.

Section width

Increasing section width at the same aspect ratio makes the sidewall taller as well as wider. At a 75 aspect ratio, every extra 10 mm of width adds 7.5 mm of sidewall height and 15 mm of overall diameter. A wider tire is therefore usually a taller tire, unless the aspect ratio drops at the same time.

Aspect ratio

Changing the aspect ratio at the same width changes the sidewall height in proportion. A 315-wide tire has a 220.5 mm sidewall at a 70 ratio and a 252 mm sidewall at an 80 ratio. That difference of 31.5 mm per sidewall means 315/80R22.5 is about 63 mm taller overall than 315/70R22.5.

Rim diameter

A change in rim diameter changes overall diameter by the same amount if the sidewall stays the same. Moving from a 22.5-inch to a 24.5-inch rim adds 2 inches (50.8 mm) to overall diameter. This is why 24.5-inch sizes often use lower profiles: the shorter sidewall compensates for the larger wheel. In practice, a change of rim diameter also means different wheels, so it is never just a tire swap.

Example size comparisons

The comparisons below use calculated overall diameters. They show how sizes that look very different can be almost the same height, and how sizes that look similar can differ noticeably.

Comparison	Calculated diameter difference	What it shows
295/75R22.5 vs 315/70R22.5	1,014 vs 1,013 mm (about 1.5 mm)	A wider tire with a lower ratio can match the height of a narrower tire
295/75R22.5 vs 445/50R22.5	1,014 vs 1,017 mm (about 2.5 mm, 0.25%)	A wide-base single is sized to match the height of common dual sizes
315/80R22.5 vs 385/65R22.5	1,076 vs 1,072 mm (about 3.5 mm, 0.3%)	70 mm more width with almost no change in height
295/75R22.5 vs 285/75R24.5	1,014 vs 1,050 mm (about 36 mm, 3.5%)	Same ratio but a larger rim adds height; the two need different wheels
295/75R22.5 vs 315/80R22.5	1,014 vs 1,076 mm (about 62 mm, 6.1%)	Higher width and ratio together produce a clearly taller tire
275/70R22.5 vs 295/75R22.5	957 vs 1,014 mm (about 58 mm, 6.0%)	Same rim diameter, but a lower, narrower bus size is much shorter

A difference in overall diameter changes road speed for the same wheel rotation. If a vehicle's speed measurement is set for 295/75R22.5 and the vehicle is fitted with 315/80R22.5 without recalibration, the tire covers about 6.1% more distance per revolution. When the vehicle shows 100 km/h, it is actually travelling at about 106 km/h. Odometer and tachograph readings are affected in the same proportion.

Off-road tire size chart: how are on/off-road truck sizes read?

On/off-road and off-road truck tires use the same size designations as highway tires, so they are read the same way. They often have higher aspect ratios or larger nominal widths, which give taller sidewalls for ground clearance and flotation. Construction tippers, mixers and heavy all-terrain trucks commonly use sizes such as 315/80R22.5 and 13R22.5. Specialist off-road trucks use high-profile sizes such as 365/85R20, 395/85R20 and 14.00R20.

Size	Format	Sidewall height (calc.)	Overall diameter (calc.)
315/80R22.5	Metric	252 mm	1,076 mm (42.3 in)
13R22.5	Numeric, no aspect ratio	Not calculable from the marking	Manufacturer data
365/85R20	Metric, high profile	310.3 mm	1,129 mm (44.4 in)
395/85R20	Metric, high profile	335.8 mm	1,180 mm (46.4 in)
14.00R20	Numeric, no aspect ratio	Not calculable from the marking	Manufacturer data

Off-road tread patterns have deep, open blocks. Because of this, the published overall diameter of an off-road tire can differ from that of a highway tire in the same size more than it would between two highway patterns. Light-truck off-road sizes written as diameter × width, such as 35x12.50R17, state the overall diameter directly. That format belongs to light trucks, not to heavy commercial vehicles. Large earthmover sizes such as 29.5R25 are a separate category of off-the-road equipment tires.

Why is calculated geometry different from actual tire dimensions?

A calculated overall diameter is a nominal value based only on the size designation. The actual dimensions of a commercial tire depend on the specific model, its construction and how it is measured. Manufacturers measure new tires on a specified rim at a specified inflation pressure, and the standards allow tolerances around the nominal values. Several factors cause real tires to differ from the calculation.

• Tread depth and pattern: Drive and off-road tires usually have deeper treads than steer or trailer tires of the same size, which adds overall diameter.
• Rim width: Mounting a tire on a wider or narrower approved rim changes the measured section width slightly.
• Load and inflation: Under load, the tire flattens at the contact patch. The static loaded radius is smaller than half the unloaded diameter, which is why measured revolutions per mile exceed the calculated figure.
• Wear: As tread wears, overall diameter and circumference decrease. A worn tire and a new tire of the same size are not the same height.
• Nominal width is not tread width: Section width is measured across the sidewalls, not across the tread face.

For any decision that depends on exact size, such as matching dual tires, setting speed calibration or checking clearance, use the overall diameter and revolutions per mile or per kilometre published for the exact tire model. Do not rely on the calculation alone. Dual tires on the same axle end should be matched within the tolerance specified by the tire manufacturer, because a taller tire in a dual pair carries more than its share of the load.

Does a similar overall diameter mean two sizes are interchangeable?

No. Similar calculated or published overall diameter shows only that two sizes are of similar height. It does not confirm that one can replace the other on a given truck or bus. Fitment compatibility also depends on several other factors.

• Rim diameter and rim width: The tire must match the wheel's diameter and be approved for its width. A 22.5-inch tire cannot be mounted on a 24.5-inch wheel.
• Load index and inflation: The replacement must meet the axle's required load at the available inflation pressure, in single or dual configuration as used.
• Speed symbol: The rating must suit the vehicle's operating speed.
• Clearance: A wider tire needs space to the chassis, suspension, brake components and the other tire in a dual pair, and room to turn at full steering lock.
• Wheel offset and track: Replacing duals with a wide-base single such as 445/50R22.5 requires suitable wheels and changes the load path on the axle.
• Vehicle and legal requirements: The vehicle manufacturer's approved sizes and local regulations apply, including speed-recording calibration.

Use size markings and diameter calculations to understand and compare tire geometry. Treat them as a starting point, not a final fitment answer. For example, 295/75R22.5 and 445/50R22.5 are nearly identical in calculated height, yet they are installed in different configurations, on different wheels, with different load ratings. Changing from one size to another on a commercial vehicle should be confirmed against the vehicle manufacturer's specifications and the tire manufacturer's data.