Tractor-Trailer Tire Size Chart Explained: How to Read and Compare Semi Truck Tire Sizes

A tractor-trailer tire size chart lists the size codes molded on the tire sidewall, such as 295/75R22.5 or 11R22.5, along with the dimensions and load ratings behind them. In a metric code like 295/75R22.5, 295 is the section width in millimeters, 75 is the aspect ratio (sidewall height as a percentage of width), R means radial construction, and 22.5 is the rim diameter in inches. Characters after the size, such as 144/141L, are performance ratings: load indexes for single and dual mounting, and a speed symbol. With the width, aspect ratio and rim diameter, you can calculate a tire's approximate sidewall height, overall diameter and circumference. The exact measurements and whether the tire fits a vehicle come from the manufacturer's data and the vehicle's specifications, not from the size code alone.

How do you read the numbers on a tractor-trailer tire sidewall?

A tractor-trailer tire sidewall carries two kinds of information: the size designation, which describes dimensions, and the service description, which describes load and speed capability. A typical marking on a commercial truck tire reads like this:

295/75R22.5 144/141L Load Range G

Marking	Type of value	Meaning
295	Dimension (millimeters)	Nominal section width: the width of the inflated tire from sidewall to sidewall, measured on a specified rim
75	Ratio (percent)	Aspect ratio: sidewall height equals 75% of the section width
R	Construction code	Radial construction
22.5	Dimension (inches)	Rim diameter: the wheel diameter the tire is designed to mount on
144/141	Performance rating (index)	Load index for single mounting / load index for dual mounting
L	Performance rating (symbol)	Speed symbol; L corresponds to 120 km/h (75 mph)
Load Range G	Performance rating (category)	Strength category that relates to the inflation pressure the tire can carry; Load Range G corresponds to a 14 ply rating

The key point is that the units are mixed on purpose. In a metric truck tire size, the width is in millimeters, the rim is in inches, and the aspect ratio has no unit because it is a percentage.

Metric size designations: 295/75R22.5, 275/80R22.5, 445/50R22.5

A metric size designation gives you all three numbers needed to calculate tire geometry: section width in millimeters, aspect ratio in percent, and rim diameter in inches. That is why most semi truck tire size charts that show calculated diameters use metric sizes. Common examples include 295/75R22.5 and 275/80R22.5 for tractors and trailers, low-profile sizes such as 255/70R22.5 and 275/70R22.5, 285/75R24.5 for 24.5-inch wheels, and wide-base singles such as 445/50R22.5 and 385/65R22.5.

Inch size designations: 11R22.5 and 11R24.5

An inch size designation such as 11R22.5 gives a nominal section width in inches (11), radial construction (R), and the rim diameter in inches (22.5). It does not include an aspect ratio. Without that number, you cannot calculate the sidewall height or overall diameter from the size code alone. For 11R22.5, 11R24.5 and similar inch sizes, use the overall diameter published in the manufacturer's data book or spec sheet. The 11R sizes are generally taller than their nearest low-profile metric counterparts, 295/75R22.5 and 285/75R24.5. Check the actual published diameters rather than assuming the two are interchangeable.

Performance ratings: load index, speed symbol and load range

Performance ratings describe what a tire can carry and how fast it is rated to run. They do not describe its size.

• Load index (single/dual): Commercial truck tires usually show two load indexes. In 144/141, the index 144 equals 2,800 kg (about 6,175 lb) per tire in single mounting. The index 141 equals 2,575 kg (about 5,675 lb) per tire in dual mounting. Each tire in a dual pair is rated lower than a single tire, but the pair together carries more, about 11,350 lb in this example. These loads apply at the inflation pressure the manufacturer specifies.
• Speed symbol: The letter after the load index is the maximum speed the tire is rated for under its rated load. For example, J = 100 km/h (62 mph), K = 110 km/h (68 mph), L = 120 km/h (75 mph) and M = 130 km/h (81 mph).
• Load range: A letter such as G or H indicates a strength category. Load Range G corresponds to a 14 ply rating, and Load Range H corresponds to a 16 ply rating. The same size can come in different load ranges with different load capacities.
• Maximum load and pressure statement: The sidewall also states the maximum load for single and dual use and the matching cold inflation pressure, in both metric and imperial units.
• DOT code: The last four digits give the week and year of manufacture. For example, 2324 means the 23rd week of 2024. This is an identification marking, not a size value.

How do you calculate semi truck tire diameter from the size?

You can calculate the approximate overall diameter of a metric semi truck tire by adding twice the sidewall height to the rim diameter. Because the width is in millimeters and the rim is in inches, convert to one unit first. One inch equals 25.4 mm.

1. Calculate sidewall height in millimeters: section width × aspect ratio ÷ 100.
2. Convert sidewall height to inches: sidewall height (mm) ÷ 25.4.
3. Calculate overall diameter in inches: rim diameter + (2 × sidewall height in inches).
4. Calculate circumference in inches: overall diameter × π (about 3.1416).
5. Estimate revolutions per mile: 63,360 (inches in a mile) ÷ circumference.

Worked example, 295/75R22.5:

• Sidewall height: 295 × 0.75 = 221.25 mm, or 8.71 in.
• Overall diameter: 22.5 + (2 × 8.71) = 39.92 in.
• Circumference: 39.92 × 3.1416 ≈ 125.4 in.
• Calculated revolutions per mile: 63,360 ÷ 125.4 ≈ 505.

This is calculated geometry for an idealized, unloaded tire. The actual diameter and revolutions per mile published by a manufacturer can differ, as explained below.

Semi truck tire size chart in inches (calculated values)

The table below converts common metric commercial truck tire sizes into inches, using the formulas above. All values are calculated from the size code, rounded, and are not manufacturer measurements. Inch sizes such as 11R22.5 and 11R24.5 are omitted because their size codes contain no aspect ratio.

Size	Section width (in)	Sidewall height (in)	Rim diameter (in)	Calculated overall diameter (in)	Calculated circumference (in)	Calculated revs per mile
255/70R22.5	10.04	7.03	22.5	36.56	114.9	552
275/70R22.5	10.83	7.58	22.5	37.66	118.3	536
275/80R22.5	10.83	8.66	22.5	39.82	125.1	506
295/75R22.5	11.61	8.71	22.5	39.92	125.4	505
315/80R22.5	12.40	9.92	22.5	42.34	133.0	476
385/65R22.5	15.16	9.85	22.5	42.20	132.6	478
445/50R22.5	17.52	8.76	22.5	40.02	125.7	504
285/75R24.5	11.22	8.42	24.5	41.33	129.8	488

A useful pattern appears in the 22.5 truck tire size chart rows. Sizes with very different widths and aspect ratios, such as 275/80R22.5, 295/75R22.5 and 445/50R22.5, calculate to nearly the same overall diameter. This is because the sidewall height comes out similar even though the numbers on the sidewall look quite different.

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

Overall tire diameter depends on rim diameter plus two sidewall heights, and sidewall height depends on both section width and aspect ratio. Changing any one of the three numbers changes the geometry, but in different ways.

Section width

At the same aspect ratio, a wider tire also has a taller sidewall, because the aspect ratio is a percentage of the width. For example, 275/80R22.5 has a calculated sidewall of 8.66 in, while 315/80R22.5 has 9.92 in. The extra 40 mm of width adds about 1.26 in to each sidewall and about 2.5 in to the calculated overall diameter.

Aspect ratio

At the same width, a lower aspect ratio means a shorter sidewall and a smaller overall diameter. For example, 275/80R22.5 calculates to 39.82 in, while 275/70R22.5 calculates to 37.66 in. Ten points of aspect ratio on a 275 mm tire is 27.5 mm per sidewall, or about 2.17 in of overall diameter. This is why low-profile sizes such as 255/70R22.5 and 275/70R22.5 are associated with lower deck heights on some trailers.

Rim diameter

A larger rim diameter adds directly to overall diameter, inch for inch. It does not change sidewall height. Comparing 22.5-inch and 24.5-inch sizes, the 2-inch rim difference is partly offset when the larger-rim tire has a shorter sidewall. For example, 285/75R24.5 has a slightly shorter calculated sidewall (8.42 in) than 295/75R22.5 (8.71 in), yet a larger overall diameter (41.33 in vs. 39.92 in).

Worked comparison: 295/75R22.5 vs. 285/75R24.5

• Calculated overall diameter difference: 41.33 − 39.92 = 1.41 in, about 3.5% larger.
• Calculated circumference difference: 129.8 − 125.4 ≈ 4.4 in per revolution.
• Calculated change in axle height: half the diameter difference, about 0.7 in.
• Calculated speedometer effect: if a speedometer were calibrated for the 39.92 in tire, an indicated 65 mph would be about 65 × 1.035 ≈ 67.3 mph on the 41.33 in tire.

Worked comparison: 445/50R22.5 wide single vs. dual 295/75R22.5

• Calculated overall diameter: 40.02 in vs. 39.92 in, nearly the same height.
• Width: one 445 mm tire is about 17.5 in wide, while two 295 mm tires total about 23.2 in of tire width before any dual tire spacing is added.
• Meaning: in a semi truck tire size comparison chart, similar diameter only tells you the rolling height is close. Load capacity, wheel offset, track width and axle-end setup are separate questions that the size code does not answer.

How do you read a commercial truck tire size chart PDF?

A manufacturer's commercial truck tire size chart PDF, or data book, lists measured and rated values for each size and tread design. Calculated values from the size code are only an estimate. Common columns include:

• Size and load range: The sidewall designation and strength category, such as 11R22.5 LRG.
• Tread depth: Usually in 32nds of an inch. Drive, steer and trailer designs in the same size often have different tread depths.
• Approved and measuring rim widths: The wheel widths the tire may be mounted on, and the width used when measuring it.
• Overall diameter and section width: Measured on the specified rim at the specified inflation pressure, without load.
• Static loaded radius: The distance from the axle center to the ground under rated load, which is less than half the unloaded diameter.
• Revolutions per mile: Based on the tire's actual rolling behavior. It is often different from the simple 63,360 ÷ circumference calculation.
• Minimum dual spacing: The smallest recommended center-to-center distance between dual tires.
• Maximum load and pressure, single and dual: Matching the load indexes on the sidewall.

When comparing sizes across brands, compare the same columns from each maker's chart. Do not mix one brand's measured diameter with another size's calculated diameter.

Why do calculated tire dimensions differ from actual tire dimensions?

Calculated tire dimensions are based on nominal size code values, while actual tire dimensions depend on how a specific tire is built, mounted, inflated and worn. Common reasons for the difference include:

• Nominal values: Section width and aspect ratio are rounded design designations, not exact measurements.
• Tread design and depth: A deep drive tread makes a tire taller than a shallow trailer tread in the same size.
• Wear: Tread wear reduces diameter by twice the tread depth worn off. Wearing away 20/32 in of tread reduces overall diameter by 40/32 in, or 1.25 in.
• Rim width and inflation: Section width and diameter change slightly with the rim width and inflation pressure used.
• Load: Under load, the tire deflects. The loaded radius is smaller than half the unloaded diameter, which is why measured revolutions per mile usually differ from the calculated figure.

Because of these factors, use calculated geometry to understand and compare sizes. Use manufacturer data when an exact number matters.

What a tire size comparison chart cannot tell you about fitment

A semi truck tire size comparison chart shows dimensional differences, not whether a tire is approved or safe for a particular tractor or trailer. Similar calculated diameters do not mean two sizes are interchangeable. Fitment also depends on:

• Load capacity: The tire's single or dual load rating at the specified pressure must meet the axle load.
• Wheel compatibility: Rim diameter, rim width, wheel offset and wheel load rating must match the tire maker's approvals.
• Dual tire spacing: Duals need at least the manufacturer's minimum spacing so the sidewalls do not touch under load. Paired duals should also be matched in diameter within the tolerances recommended by tire makers and industry practice.
• Clearance: Taller or wider tires need room at fenders, frames, suspension parts and mud flaps, including when articulating, turning and fully loaded.
• Drivetrain and electronics: Changes in revolutions per mile affect road speed at a given engine speed, speedometer and odometer readings, and settings in vehicle electronic systems.
• Vehicle and regulatory requirements: The vehicle manufacturer's specifications and applicable rules for the vehicle's use still apply.

Key points for interpreting tractor-trailer tire sizes

• In metric sizes such as 295/75R22.5, width is in millimeters, aspect ratio is a percentage, and rim diameter is in inches.
• Inch sizes such as 11R22.5 have no aspect ratio, so diameter must come from manufacturer data.
• Load index, speed symbol and load range are ratings, not dimensions.
• Overall diameter = rim diameter + 2 × sidewall height. Circumference = diameter × π.
• Calculated geometry is an estimate. Measured diameter, loaded radius and revolutions per mile come from the manufacturer's chart.
• A matching diameter does not establish fitment. Load capacity, wheels, dual spacing, clearance and vehicle specifications must all be checked separately.