Fleet & Auto Reference Library · Measure & Identify
Reading a Truck Tire Sidewall & DOT Code
How to read size, construction, load range, load index, speed symbol and the DOT Tire Identification Number on a truck tire, so the right replacement is quoted and tire age can be checked.
Safety-critical sheet, not yet signed off by an expert reviewer. Use it to understand the topic, then take every value and decision from the governing standard, the manufacturer’s instructions and a qualified person.
What it is
Every highway tire sold in the U.S. carries molded markings that describe its size and construction, its load and speed capability, and a Tire Identification Number (TIN) beginning with "DOT." FMVSS No. 119 (49 CFR 571.119) covers markings and performance for tires on vehicles other than passenger cars, 49 CFR 574.5 defines the TIN format, and 49 CFR 393.75 sets in-service tire requirements for commercial motor vehicles. The sidewall is the primary source for matching a replacement and for checking age and load capacity.
How to identify
Use the example 295/75R22.5 144/141L LR G and the TIN DOT XXX XXXX 2324.
- Size — metric style (295/75R22.5): 295 = nominal section width in millimeters; 75 = aspect ratio (sidewall height as a percentage of width); R = radial construction; 22.5 = rim diameter in inches.
- Size — conventional style (11R22.5): 11 = nominal section width in inches; R = radial; 22.5 = rim diameter. Conventional and metric sizes are not automatically interchangeable even when they look similar.
- Load index (144/141): two numbers on truck tires — the first for single fitment, the second for dual fitment. Each number corresponds to a maximum load in the load index table.
- Speed symbol (L): maximum speed category for the tire under its rated conditions.
- Load range (LR G): a letter replacing the old ply-rating number; a higher letter means the tire is built for more load at higher inflation.
- Maximum load and inflation: molded as words and numbers, for single and dual. Read them from the tire — do not estimate.
- TIN: "DOT," then the plant code, then optional size and manufacturer codes, then a four-digit date code — week then year. 2324 = week 23 of 2024.
Sidewall markings at a glance
| Marking | Example | Meaning |
|---|---|---|
| Section width | 295 | Nominal width in mm (metric sizing) |
| Aspect ratio | 75 | Sidewall height as % of width |
| Construction | R | Radial |
| Rim diameter | 22.5 | Inches |
| Load index, single/dual | 144/141 | Look up the maximum load in the load index table or on the sidewall |
| Speed symbol | L | Speed category; L corresponds to 120 km/h (75 mph) |
| Load range | G | Ply-rating equivalent 14 |
| Load range | H | Ply-rating equivalent 16 |
| Date code | 2324 | Week 23, year 2024 |
Key points
- Replacement tires must have at least the load capacity the vehicle needs at each position, single or dual. Use the load index and the maker's load/inflation tables — never guess.
- Duals must be matched for size and closely matched for diameter; mismatched duals overload one tire.
- The full TIN with the date code may appear on only one sidewall. Check both sides before deciding it is missing.
- Retreaded tires carry an additional retreader identification. Some retreads and regrooved tires are restricted on certain axle positions — see 49 CFR 393.75.
- Tire and wheel work carries serious injury risk. Mounting, inflation and multi-piece rim work fall under 29 CFR 1910.177.
Common mistakes
- Swapping 11R22.5 and 295/75R22.5 without checking diameter, load and fitment.
- Reading the dual load index as the single load index.
- Treating a three-digit date code (pre-2000) or the plant code as the build date.
- Matching by size alone and missing a load range difference.
Governing standards: 49 CFR 574.5 (tire identification requirements); FMVSS No. 119, 49 CFR 571.119 (new pneumatic tires for vehicles other than passenger cars); 49 CFR 393.75 (tires on commercial motor vehicles); 29 CFR 1910.177 (servicing rim wheels). Tire maker's load and inflation tables.
Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.