Aircraft Tire Size and Dimension Chart: Reading the Numbers on the Sidewall

An aircraft tire size is the designation molded into the sidewall. It uses one of three naming systems:

• Overall diameter x section width, for example 49x17
• Section width - rim diameter, for example 6.00-6
• Three-part overall diameter x section width - rim diameter, for example 30x8.8R15

Most designations are in inches. Metric designations give diameter and width in millimetres. A dash usually means a bias-ply tire, and an R means a radial tire. The other numbers on the sidewall are performance ratings, not dimensions. These include ply rating, speed rating, rated load and rated inflation pressure. To compare sizes, you can calculate sidewall height and circumference from the size, but actual dimensions and approval to fit an aircraft come from manufacturer and aircraft data.

What Do the Numbers on an Aircraft Tire Sidewall Mean?

The size designation on an aircraft tire sidewall states the tire's nominal dimensions. Depending on the naming system, these are overall diameter, section width, rim diameter, or a combination. Overall diameter is the height of the inflated tire from tread to tread. Section width is the widest point across the sidewalls. Rim diameter is the diameter of the wheel bead seat the tire mounts on.

The Three Aircraft Tire Size Naming Systems

Aircraft tires are named by type. The type determines which dimensions appear in the size and which you must look up in a chart.

Dash, R and Prefix Letters

The separator before the rim diameter indicates construction. A dash, as in 46x16.0-20, indicates bias-ply construction. An R, as in 30x8.8R15, indicates radial construction. A bias tire and a radial tire with otherwise identical numbers are different tires, and they are not automatically interchangeable.

Some three-part sizes begin with a letter such as H or B, as in H49x19.0-22. The prefix identifies a particular design standard. It relates to the wheel rim width compared with the tire's section width, and to the bead seat design. Treat the prefix as part of the size. An H tire and a non-prefixed tire with similar numbers are not the same size.

Which Sidewall Markings Are Ratings, Not Dimensions?

Several aircraft tire sidewall markings describe strength, speed, load or service history rather than size. They help you compare capability but say nothing about how big the tire is.

• Ply rating (PR): An index of carcass strength, for example 6 PR or 32 PR. It is not a literal count of fabric plies, and it does not tell you the tire's thickness.
• Speed rating: The maximum ground speed the tire is qualified for, in miles per hour (mph), for example 225 mph.
• Rated load: The maximum static load per tire at rated pressure, usually in pounds (lb).
• Rated inflation: The inflation pressure that corresponds to the rated load, usually in pounds per square inch (psi). The aircraft's own service pressure is set by the aircraft data and may differ.
• TL or TT: Tubeless or tube-type construction.
• Approval and identification marks: Manufacturer, part number, serial number and technical standard order marking.
• Retread marking: Indicates that the tire has been retreaded and, typically, how many times.
• Balance and vent marks: A balance mark shows the light spot of the tire. Vent marks on tubeless tires show where trapped gas can escape through the lower sidewall. Neither is a dimension.

How to Read an Aircraft Tire Size Step by Step

1. Find the size designation. It is usually the largest group of numbers on the sidewall, such as 6.00-6, 49x17 or 30x8.8R15.
2. Identify the format. Two numbers joined by a dash is a section width - rim diameter size. Two numbers joined by x is an overall diameter x section width size. Three numbers is a three-part size.
3. Check the units. Values under about 60 are normally inches. Values in the hundreds or thousands, such as 1400x530, are millimetres for diameter and width. The rim diameter is still in inches.
4. Note the construction and any prefix. A dash means bias and an R means radial. Keep any H or B prefix as part of the size.
5. Separate the ratings. Read the ply rating, speed rating, load and pressure as capability information, not dimensions.
6. Look up the missing dimension. Use the manufacturer's dimension chart to find the overall diameter of a Type III tire or the rim diameter of a Type VII tire.

How to Calculate Sidewall Height, Aspect Ratio and Circumference

Once you know overall diameter, section width and rim diameter, you can calculate nominal geometry using three formulas. The results are approximations for comparison, not measured values.

• Sidewall (section) height = (overall diameter - rim diameter) / 2
• Aspect ratio = section height / section width
• Circumference = π x overall diameter

Example 1, 30x8.8R15:

• Section height = (30 - 15) / 2 = 7.5 in
• Aspect ratio = 7.5 / 8.8 ≈ 0.85, so the sidewall is about 85% as tall as the tire is wide
• Circumference = π x 30 ≈ 94.2 in

Example 2, H49x19.0-22:

• Section height = (49 - 22) / 2 = 13.5 in
• Aspect ratio = 13.5 / 19.0 ≈ 0.71
• Circumference = π x 49 ≈ 153.9 in, about 12.8 ft or 3.9 m

Example 3, metric 1400x530R23. First convert the rim diameter: 23 in x 25.4 = 584.2 mm. Then:

• Section height = (1400 - 584.2) / 2 ≈ 408 mm
• Aspect ratio = 408 / 530 ≈ 0.77
• Circumference = π x 1400 ≈ 4,398 mm, about 4.4 m

Example 4, Type III 6.00-6. The overall diameter is not in the size, so you need a chart value. For illustration, if a chart listed an overall diameter of 17.5 in:

• Section height = (17.5 - 6) / 2 = 5.75 in
• Aspect ratio = 5.75 / 6.00 ≈ 0.96, which reflects the tall, rounded profile typical of low-pressure Type III tires

How Width, Aspect Ratio and Rim Diameter Interact

For a given overall diameter, a larger rim diameter leaves less room for the sidewall. Compare 49x17 on a 20 in rim with H49x19.0-22 on a 22 in rim:

• Both have a nominal overall diameter of 49 in and the same nominal circumference of about 153.9 in.
• The 49x17 has a section height of (49 - 20) / 2 = 14.5 in and an aspect ratio of about 0.85.
• The H49x19.0-22 is wider, has a shorter sidewall of 13.5 in, and has a lower aspect ratio of about 0.71.

The same nominal height does not mean the same tire. These two sizes need different wheels.

Aircraft Tire Size Chart: Example Designations Decoded

The chart below decodes example designations and shows nominal geometry calculated from the size. Values marked from chart are not contained in the size itself. All figures are nominal calculations, not catalogue or measured dimensions.

How Big Are Tires on an Airplane?

The size of airplane tires depends on aircraft weight, landing gear design and speed. Light aircraft use small, low-pressure tires with overall diameters measured in the teens of inches. Large jet airliners use main landing gear tires roughly 46 to 56 in tall, with section widths of about 16 to 21 in.

On the same aircraft, nose gear tires are often smaller than main landing gear tires because the main gear carries most of the weight. A common light-aircraft pattern is a 5.00-5 nose tire with 6.00-6 main tires.

How Tall Are Airplane Tires?

The height of an airplane tire is its overall diameter. In a Type VII or three-part size, it is the first number:

• A 49x17 tire is about 49 in, or 1.24 m, tall when inflated and unloaded.
• A 1400x530R23 tire is about 1.4 m, or 55 in, tall.
• For Type III light-aircraft tires such as 6.00-6, the height is not in the size and must be read from the manufacturer's dimension chart.

Under the aircraft's weight, the tire deflects, so its loaded height above the ground is less than the overall diameter.

How Big Are the Tires on a 747?

The Boeing 747 rolls on 18 tires: 16 on the main landing gear and 2 on the nose gear. On the 747-400, the main landing gear tires are commonly listed as H49x19.0-22. That means:

• Overall diameter about 49 in (about 1.24 m)
• Section width about 19 in (about 0.48 m)
• Mounted on a 22 in wheel
• Calculated sidewall height about 13.5 in
• Calculated circumference about 12.8 ft

Other 747 variants use different tire sizes. The exact designation, ply rating and pressure for a specific aircraft come from that model's approved maintenance data, not from a general chart.

How Thick Are Airplane Tires?

The thickness of an airplane tire is not marked on the sidewall and cannot be calculated from the size designation. Thickness varies across the tire:

• Tread thickness is the rubber available for wear above the reinforcing layers. It is checked as groove depth against the manufacturer's wear limits.
• Carcass thickness is the reinforcing body built from fabric plies and rubber. It is generally greater on tires with higher ply ratings, but the ply rating is not a measurement of thickness.
• Sidewall thickness differs from thickness under the tread.

Detailed layer thicknesses are rarely published in a general aircraft tire size chart.

Why Calculated Geometry Is Not the Actual Tire Dimension

Calculated sidewall height, aspect ratio and circumference describe the nominal size, not the dimensions of a specific tire on an aircraft. Real dimensions differ for several reasons:

• Nominal rounding. A 49 in size is a name. The manufacturer specifies an allowable range of inflated overall diameter and section width.
• Growth. New aircraft tires stretch after mounting and inflation. Data books may list both new and grown dimensions, and a stabilization period is usually specified before final pressure checks.
• Load. Under aircraft weight the tire flattens. The static loaded radius, measured from the axle centre to the ground, is smaller than half the overall diameter. The loaded rolling circumference is also smaller than π x diameter.
• Construction and wear. Bias and radial tires of the same nominal size can have different profiles. A worn tire has a smaller diameter than a new one.

Does a Matching Size Mean a Tire Fits the Aircraft?

Matching size numbers do not make a tire approved or compatible for a particular aircraft. Fitment depends on several conditions beyond overall diameter:

• The wheel's rim diameter, rim width and bead seat design
• Bias or radial construction
• Ply rating, rated load and speed rating at least meeting the aircraft's requirements
• Grown and loaded dimensions that clear the gear structure, brakes and wheel well during retraction
• The tire being listed in the aircraft's or wheel's approved data

Two sizes with the same calculated circumference, such as 49x17 and H49x19.0-22, can require entirely different wheels.

What an Aircraft Tire Dimensions Chart or PDF Data Book Contains

Aircraft tire manufacturers publish dimension charts, often as PDF data books. These charts list measured specifications that the sidewall size cannot provide. Typical columns include:

• Size designation, ply rating and tubeless or tube-type
• Speed rating (mph), rated load (lb) and rated inflation pressure (psi)
• Inflated overall diameter and section width, often as maximum and minimum values
• Grown dimensions after service stretch
• Shoulder diameter and shoulder width
• Static loaded radius and flat-tire radius
• Recommended rim width and wheel size
• Tire weight and part number

To use an airplane tire size chart, look up the size by its exact designation, including any prefix and the dash or R. Then read the dimensions and ratings for the specific ply rating and part number. That row, not the calculated geometry, describes the real tire.