Free wheel and tyre tools
Tyre code and DOT date decoder
Decode a tyre sidewall such as 245/40 ZR18 97Y XL. Look up load indices 60–130, speed ratings and the approximate age from a four-digit DOT date.
How it works
The width is in millimetres, the profile is a percentage of width and the rim is in inches. R means radial; ZR is a high-speed radial designation whose service description gives the more specific rating. Load index maps to a rated mass per tyre under specified conditions, not a vehicle payload. XL and a separate RF suffix mean reinforced load capacity; RF in the construction position denotes run-flat construction. The final four DOT date digits give production week and year from 2000 onwards. Age uses the midpoint of that Sunday-to-Saturday week and your device's current date, so it is approximate.
References
A worked example
245/40 ZR18 97Y XL describes a nominal 245 mm section width, a 98 mm sidewall and an 18 inch radial tyre. Load index 97 is 730 kg per tyre at the specified conditions; Y is a 300 km/h laboratory speed rating (about 186 mph). XL means extra load. DOT date 2322 means week 23 of 2022, not the 23rd month.
Quick reference
Speed ratings
| Rating | km/h | mph |
|---|---|---|
| Q | 160 | 99 |
| R | 170 | 106 |
| S | 180 | 112 |
| T | 190 | 118 |
| H | 210 | 130 |
| V | 240 | 149 |
| W | 270 | 168 |
| Y | 300 | 186 |
Selected load indices
| Load index | kg per tyre |
|---|---|
| 80 | 450 |
| 84 | 500 |
| 88 | 560 |
| 91 | 615 |
| 94 | 670 |
| 97 | 730 |
| 100 | 800 |
| 104 | 900 |
| 108 | 1000 |
| 112 | 1120 |
Capacity per tyre at the specified pressure and conditions, not a vehicle payload.
Explained in our guides
- How to read a tyre size, load index and sidewall markingsDecode tyre width, aspect ratio, rim diameter, load and speed markings, then calculate sidewall height and diameter using a 225/45 R17 example.
- Wheel load ratings, JWL, VIA and TÜV: what to checkScreen wheel load capacity against axle requirements, understand JWL and VIA markings, and read TÜV-related documents for the exact wheel and application.
Questions
How old is too old for a tyre?
Age alone cannot establish condition. Michelin recommends annual professional checks after five years in use and precautionary replacement ten years after manufacture. This tool flags five years since manufacture as a conservative prompt because it cannot know when the tyre entered service. Follow any earlier replacement limit from your car or tyre maker.
Does RF always mean run-flat?
No. A separate RF or REINF load marking means reinforced. RF replacing R in the size construction position can denote run-flat construction. Brand markings such as RFT, ROF, SSR and ZP also need the tyre maker's instructions. Extra load alone does not make a tyre run-flat.
What is the difference between Y and (Y)?
Y identifies a 300 km/h rating. A bracketed Y service description, commonly written (97Y), indicates capability above 300 km/h subject to tyre maker limits. Neither marking is a recommended driving speed. Load capacity can reduce at high speeds.
Can I enter an entire DOT serial number?
Use only its final four date digits in the date field. The complete date may be on just one sidewall. Three-digit date codes predate 2000; this tool will flag them rather than guess a decade. Dual load indices and inch-format sizes are outside this decoder's scope.
Keep checking
Use these results to plan a setup. Confirm fitment, tyre approval and clearances with a qualified professional before buying or fitting parts.