Common Ways to Express OTR and Industrial Tire Sizes/Specs
Choosing the right tire starts with understanding how tire sizes are written. For OTR, construction, mining, port, forklift, skid steer, and other industrial applications, tire specifications may look different depending on the tire type, structure, and usage conditions.
This guide explains the most common ways to read engineering and industrial tire size markings.
1.Radial Tire Size Format
A common Radial OTR tire size may be written like this:
17.5 R 25 NHS ★/★★ TT/TL
Each part has a specific meaning:
- 17.5— Nominal section width of the tire, usually expressed in inches.
- R— Radial construction. If there is no “R”, the tire may be a bias construction. Radial tires are widely used in many heavy-duty applications because they often provide improved heat dissipation, better traction, and longer service life under suitable working conditions.
- 25— Rim diameter in inches.
- NHS— Application or service marking.
- NHS means “Not for Highway Service”.
- ★/★★— Star rating, commonly used to indicate tire strength or load capacity category.
- TT/TL— Tube type or tubeless type.
- TT means Tube Type.
- TL means Tubeless.
- Some Tires may be used both with a tube and without a tube.
So, a size such as 17.5R25 means the tire has a nominal section width of 17.5 inches, radial construction, and fits a 25-inch rim.
2.Metric Tire Size Format
Some industrial and engineering tires use a metric format, such as:
385/95R25
This format is common on certain cranes, special vehicles, and heavy-duty equipment.
The structure is:
Section Width / Aspect Ratio R Rim Diameter
For example:
385/95R25
means:
- 385 mm section width
- 95% aspect ratio
- Radial construction
- 25-inch rim diameter
The aspect ratio indicates the sidewall height as a percentage of the tire width. In this case:
385 × 95% = 365.75 mm
So the approximate sidewall height is 365.75 mm.
3.Bias Tire Size Format
Bias OTR tires are often written without the letter “R”.
Example:
16.00-25 36PR
This can be read as:
- 16.00— Nominal section width in inches.
- – — Bias construction.
- 25— Rim diameter in inches.
- 36PR— Ply rating.
In this format, the hyphen usually indicates a bias tire.
Bias tires are still widely used in construction, industrial handling, mining, port, and underground applications because of their strong sidewalls and good resistance to impact damage.
4.Industrial Tire Format
Some industrial tires, especially forklift and skid steer tires, may be written in a format like:
23×8.5-12 8PR
This means:
- 23— Overall tire diameter in inches.
- 8.5— Nominal section width in inches.
- – — Bias construction.
- 12— Rim diameter in inches.
- 8PR— Ply rating.
This format is often used for industrial, forklift, skid steer, and some compact equipment tires.
5.What Is PR or Ply Rating?
PR stands for Ply Rating.
For example:
16.00-25 36PR
The 36PR does not always mean the tire actually has 36 physical fabric layers. Instead, it is a strength index that indicates the tire’s load-carrying capacity under specified service conditions.
In modern tire manufacturing, materials and construction have changed, so ply rating is mainly used as a reference for tire strength and load capacity.
Star Rating to Ply Rating Conversion
For many OTR and earthmoving tires, especially radial OTR tires, the tire strength may be marked by a star rating instead of a traditional ply rating. The star rating is commonly used to indicate the tire’s load-carrying capacity under specific service conditions.
In general:
- ★indicates a standard load rating for the specified application.
- ★★indicates a higher load-carrying capacity.
- ★★★indicates an even higher strength level for severe-duty or high-load applications.
However, the exact equivalent ply rating can vary depending on tire size and service type, such as transportation, loading, or industrial use.
Example Conversion Table
| Tire Size | Star Rating | Transportation | Loading | Industrial |
| 12.00R20 | ★★ | — | — | 20 |
| 12.00R24 | ★★ | — | 20 | 24 |
| 13.00R24 | ★ | 14 | 14 | — |
| 13.00R25 | ★★★ | 28 | — | — |
| 14.00R24 | ★ | — | 16 | — |
| 14.00R24 | ★★ | 28 | — | — |
| 14.00R24 | ★★★ | 32 | 28 | 28 |
| 14.00R25 | ★★ | 32 | — | — |
| 15.5R25 | ★ | 16 | — | — |
| 16.00R25 | ★★ | 36 | — | 32 |
| 16.00R25 | ★★★ | 40 | — | — |
| 17.5R25 | ★ | — | 16 | — |
| 17.5R25 | ★★ | 24 | 20 | — |
| 18.00R25 | ★★ | 36 | 36 | — |
| 18.00R25 | ★★★ | — | — | 40 |
| 20.5R25 | ★ | — | 24 | — |
| 20.5R25 | ★★ | 28 | 28 | — |
| 20.5R25 | ★★★ | — | — | 36 |
| 23.5R25 | ★ | — | 28 | — |
| 23.5R25 | ★★ | 32 | 32 | — |
| 23.5R25 | ★★★ | — | — | 36 |
| 26.5R25 | ★ | — | 32 | — |
| 26.5R25 | ★★ | 32 | 36 | — |
| 26.5R25 | ★★★ | — | — | 44 |
| 29.5R25 | ★ | — | 34 | — |
| 29.5R25 | ★★ | 34 | 38 | — |
| 29.5R25 | ★★★ | — | — | 48 |
| 29.5R29 | ★ | — | 34 | — |
| 29.5R29 | ★★ | 40 | 40 | — |
| 29.5R29 | ★★★ | — | — | 52 |
| 33.25R29 | ★ | 44 | — | — |
| 18.00R33 | ★★ | 40 | — | — |
| 18.00R33 | ★★★ | — | — | 40 |
| 21.00R35 | ★ | 32 | — | — |
| 35/65R33 | ★★ | — | 42 | — |
| 35/65R33 | ★★★ | — | 54 | 54 |
| 21.00R35 | ★★ | 44 | — | — |
| 24.00R35 | ★★ | 48 | — | — |
| 37.25R35 | ★★ | 46 | — | — |
| 27.00R49 | ★★ | 48 | — | — |
| 33.00R51 | ★★ | 68 | — | — |
Note: This table is for general reference only. Actual load capacity should always be checked according to the official data book, tire standard, rim specification, inflation pressure, and working conditions.
6. What Do TT and TL Mean?
Many OTR and industrial tires include the markings TT or TL.
- TT— Tube Type
The tire must be used with an inner tube. - TL— Tubeless
The tire is designed to be used without an inner tube, with a suitable tubeless rim.
Some tire models may be available in both TT/TL versions, depending on the size and application.
7.What Does NHS Mean?
NHS means Not for Highway Service.
This marking is commonly used on off-road tires that are designed for job sites, mines, ports, farms, warehouses, and industrial areas. Tires marked NHS are not intended for regular highway driving.
Examples include tires used for:
- Loaders
- Graders
- Skid steers
- Forklifts
- Mining dump trucks
- Industrial trailers
- Port handling equipment
8. Common Examples
Tire Size | Meaning |
23.5R25 | 23.5-inch section width, radial construction, 25-inch rim |
445/95R25 | 445 mm width, 95 aspect ratio, radial, 25-inch rim |
18.00-25 40PR | 18.00-inch width, bias construction, 25-inch rim, 40-ply rating |
28×9-15 14PR | 28-inch overall diameter, 9-inch width, 15-inch rim, 14-ply rating |
16.00-25 36PR | 16.00-inch width, bias construction, 25-inch rim, 36-ply rating |
Conclusion
Understanding OTR and industrial tire size markings helps users choose the right tire for the right equipment and working environment. Whether the tire is marked in inch format, metric format, radial format, or bias format, each number and letter provides important information about tire width, rim diameter, construction type, strength rating, and service application.
If you are not sure which size is suitable for your equipment, always check the original tire marking, rim specification, load requirement, and working conditions before selecting a replacement tire.
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