Industrial Solid Tire Sizes and Dimensions Explained

Industrial solid tire sizes come in two main formats, depending on how the tire mounts. A press-on tire is marked with three numbers, such as 21x7x15. These are the outside diameter, the tire width and the inside diameter, all in inches. A solid tire shaped like a pneumatic tire is marked in pneumatic style, such as 6.50-10, 28x9-15 or 200/50-10. The last number in these sizes is always the rim diameter in inches. The type of size marking tells you which wheel the tire fits. The numbers tell you the tire's nominal geometry.

What do the numbers on an industrial solid tire sidewall mean?

The size numbers describe three things: how tall the tire is, how wide it is, and what it mounts on. The mounting surface can be a press-on wheel seat or a rim. The meaning of each number depends on the format, so identify the format first.

Press-on tire sizes: outside diameter × width × inside diameter

A press-on tire size such as 21x7x15 means a 21 in outside diameter, a 7 in tire width and a 15 in inside diameter. Press-on tires, also called press-on bands, have rubber bonded to a steel band. The band is pressed onto a smooth wheel seat. The third number is the inside diameter of that steel band, and it must match the wheel. Other common examples include 16x6x10-1/2, 18x8x12-1/8 and 22x9x16. Fractional inside diameters such as 12-1/8 are part of the size and should not be rounded.

• First number (outside diameter): the overall height of the new tire, measured across the tread.
• Second number (tire width): the width of the tire across the tread and band.
• Third number (inside diameter): the bore of the steel band, which must equal the wheel's press-on seat diameter.

Some press-on tires are also labeled in millimeters. In that case the three numbers follow the same order: outside diameter × width × inside diameter.

Pneumatic-shaped solid tire sizes: section width and rim diameter

A pneumatic-shaped solid tire size such as 6.50-10 means a nominal section width of 6.50 in on a 10 in diameter rim. These solid tires, often called resilient or cushion solid tires, look like air-filled tires. They mount on the same kind of split or multi-piece rims. Some manufacturers use labels such as SE (super elastic) for this construction.

The size marking can take several forms:

• 6.50-10: section width in inches, then rim diameter in inches. No aspect ratio is stated, so you cannot calculate the sidewall height precisely from the marking alone.
• 28x9-15: nominal outside diameter 28 in, nominal width 9 in, rim diameter 15 in. Some tires carry two markings for the same size, such as 28x9-15 and 8.15-15.
• 18x7-8 or 23x9-10: the same pattern of outside diameter x width - rim diameter, all in inches.

The dash before the rim diameter separates the tire dimensions from the rim size. In a size like 28x9-15, the 15 is not the same kind of value as the 15 in a press-on size like 21x7x15. In the pneumatic-shaped size it is the rim diameter. In the press-on size it is the inside diameter of a steel band.

Metric solid tire sizes with an aspect ratio

A metric size such as 200/50-10 means a 200 mm section width, an aspect ratio of 50 and a 10 in rim diameter. The aspect ratio is the sidewall height as a percentage of the section width. So a 50 aspect ratio on a 200 mm wide tire gives a sidewall height of about 100 mm. This format mixes units: width in millimeters, ratio as a percentage, rim diameter in inches. Similar sizes include 140/55-9 and 180/70-8.

Which sidewall markings are not dimensions?

Many markings on an industrial solid tire describe compound, rim type or use, not size. Read them separately from the size numbers:

• Rim designation: a code such as 5.00F or 4.33R gives the recommended rim width and rim contour. It belongs to the wheel, not to the tire's outside dimensions.
• Non-marking: the tread compound is designed not to leave black marks on floors. This affects use, not size.
• Mounting system: markings for quick-lock or click-type systems, or for a particular bead design, describe how the tire locks to the rim.
• Wear indicator or wear line: shows when the tire has reached its replacement point. It does not indicate the size.
• Load and speed information: the load capacity of a solid tire depends on speed and on the manufacturer's rating. Many solid tires do not carry the load index and speed symbol familiar from road tires. Load capacity is usually given in the manufacturer's tables for the specific size and speed, not on the sidewall itself.

How do the solid tire size formats compare?

The format of the size tells you the mounting type and which numbers you can compare directly.

Format	Example	What each number means	Mounts on	Outside diameter from marking
Press-on (inch)	21x7x15	Outside diameter × width × inside diameter, inches	Smooth press-on wheel seat	Stated directly: 21 in
Pneumatic-shaped, diameter-width-rim	28x9-15	Outside diameter × width, then rim diameter, inches	Pneumatic-type rim	Stated directly: 28 in (nominal)
Pneumatic-shaped, width-rim	6.50-10	Section width in inches, then rim diameter in inches	Pneumatic-type rim	Not stated; check manufacturer dimensions
Metric with aspect ratio	200/50-10	Width in mm / aspect ratio %, then rim diameter in inches	Pneumatic-type rim	Calculable: about 454 mm

How do you calculate industrial solid tire dimensions from the size?

For most solid tire sizes you can estimate the rubber height, the overall diameter and the circumference with simple arithmetic. The result is nominal geometry, not a measured dimension.

Press-on tires: rubber thickness and circumference

The radial thickness of a press-on tire is half the difference between the outside and inside diameters. For 21x7x15: (21 − 15) ÷ 2 = 3 in. This figure includes the steel band, so the rubber alone is somewhat thinner. Circumference equals π × outside diameter: 3.1416 × 21 ≈ 66.0 in, or about 1,676 mm.

• 18x8x12-1/8: thickness (18 − 12.125) ÷ 2 ≈ 2.94 in; circumference ≈ 56.5 in.
• 22x9x16: thickness (22 − 16) ÷ 2 = 3 in; circumference ≈ 69.1 in.

Metric sizes: sidewall height and overall diameter

For a metric solid tire, sidewall height equals section width × aspect ratio ÷ 100, and overall diameter equals rim diameter plus two sidewall heights. To convert the rim diameter to millimeters, multiply by 25.4.

1. Sidewall height for 200/50-10: 200 × 0.50 = 100 mm.
2. Rim diameter: 10 × 25.4 = 254 mm.
3. Overall diameter: 254 + (2 × 100) = 454 mm, about 17.9 in.
4. Circumference: 3.1416 × 454 ≈ 1,426 mm.

For 140/55-9, the sidewall is 140 × 0.55 = 77 mm. The rim is 9 × 25.4 = 228.6 mm. The overall diameter is 228.6 + 154 ≈ 383 mm.

Inch sizes with a stated outside diameter

For a size like 28x9-15, the sidewall height equals half the difference between the outside diameter and the rim diameter. For 28x9-15: (28 − 15) ÷ 2 = 6.5 in. The circumference is 3.1416 × 28 ≈ 88.0 in. For a size like 6.50-10, the marking does not include an aspect ratio or an outside diameter. Use the manufacturer's dimension table rather than guessing.

How do width, aspect ratio and rim diameter affect diameter and circumference?

Overall diameter depends on rim diameter plus sidewall height. Sidewall height depends on both width and aspect ratio. Changing any one of the three values changes the overall diameter, unless another value changes to compensate.

• Wider tire, same aspect ratio and rim: the sidewall gets taller, so the overall diameter and circumference increase.
• Lower aspect ratio, same width and rim: the sidewall gets shorter, so the overall diameter decreases.
• Larger rim, same tire profile: the overall diameter increases by the difference in rim diameter.

Very different sizes can produce almost the same calculated diameter. A 180/70-8 has a 126 mm sidewall and an 8 in (203.2 mm) rim, giving about 455 mm overall. A 200/50-10 calculates to about 454 mm. The heights nearly match, but the widths and rim diameters differ, so the two tires do not fit the same wheel.

For press-on tires, compare sizes with the same inside diameter. A 21x7x15 and a 21x8x15 have the same outside diameter and fit the same wheel seat diameter. The second tire is 1 in wider, which matters for wheel width and clearance. A 22x8x16 is a different wheel size entirely.

Why circumference matters in practice

Circumference determines how far the machine travels with each wheel revolution. A smaller diameter means less ground covered per turn. Wear reduces outside diameter over time. If a 21x7x15 press-on tire wears from 21 in to 20 in, its circumference drops from about 66.0 in to about 62.8 in, roughly 4.8% less travel per revolution. On a truck with several driven or load wheels, mixing tires of different diameters, including one new and one worn tire, changes how the load and traction are shared.

What is the difference between nominal size and actual tire dimensions?

The size on the sidewall is a nominal size. The real measurements of a particular tire are in the manufacturer's dimension tables. Nominal numbers are rounded, standardized labels. Two tires with the same marking from different manufacturers can differ slightly in outside diameter, tread width or profile. Tread design and compound also affect actual dimensions. Calculated geometry, such as the 454 mm figure for 200/50-10, is only an estimate built from nominal values. For close clearances or for matching tires on one axle, use the manufacturer's stated outside diameter and width for the exact product.

How do you measure an industrial solid tire to identify its size?

If the sidewall marking is worn off, you can measure the tire and match the results to standard sizes.

1. Identify the type. A steel band and a smooth wheel seat mean a press-on tire. A rim with a flange or a split or multi-piece rim means a pneumatic-shaped solid tire.
2. Measure the outside diameter across the center of the tread, through the wheel center. Remember that a worn tire measures smaller than its nominal size.
3. Measure the tire width at its widest point.
4. For a press-on tire, measure the inside diameter of the steel band, or the diameter of the wheel seat. For a pneumatic-shaped tire, read the rim diameter and the rim width marking from the rim itself.
5. Compare the results with standard press-on or pneumatic-shaped sizes. Inside diameter and rim diameter must match exactly. Outside diameter and width only need to fall close to a standard size.

Does a matching size guarantee vehicle fitment?

No. A correct size reading confirms the tire's nominal dimensions, not that it suits a particular machine. A press-on tire cannot be fitted to a rim made for pneumatic-shaped tires, and the reverse is also true, even when the outside diameters are similar. Within the same format, fitment also depends on several other factors:

• the exact wheel seat or rim diameter, rim width and rim contour
• clearance to the chassis, fenders and battery compartment
• the load capacity required at the machine's operating speed
• the equipment manufacturer's specification for that model

Changing the outside diameter can also affect ground clearance, travel speed and the height of the machine. Treat size calculations as a way to understand and compare tires. Confirm the final choice against the equipment and tire manufacturers' specifications.