Tyre sidewall and DOT decoder
Type what is moulded on your tyre’s sidewall, such as 195/65 R15 91H or DOT 4R1Y 2324, to see what each part means: the size, the load each tyre may carry, its speed rating, extra-load and run-flat markings, and when it was made. The worked example decodes 195/65 R15 91H XL DOT 4R1Y 2324.
- Size
- 195/65R15 · see 195/65R15 tyres
- Width
- 195 mm, sidewall to sidewall
- Aspect ratio
- 65: the sidewall is 65% as tall as the tyre is wide (126.8 mm)
- Construction
- Radial: the cords run straight across the tyre, as on nearly every car tyre today
- Rim diameter
- 15 inches
- Overall diameter
- 634.5 mm, worked out from the size · compare it with another size
- Load index 91
- Up to 615 kg per tyre
- Speed symbol H
- Up to 210 km/h, at the load above
- XL / RF
- Extra load (reinforced): built to carry more, at a higher pressure, than a standard tyre of this size.
- DOT date
- Week 23 of 2024 (the week starting 3 June 2024)
- Age
- about 2.4 years. Under five years old. Tyre makers’ yearly inspections start at five years; until then, check the tread depth and look for cracks and bulges.
Reading the sidewall
In 195/65 R15 91H, 195 is the width in millimetres, 65 the aspect ratio (the sidewall’s height as a percentage of the width), R a radial tyre and 15 the rim diameter in inches. 91H is the service description: the load index and the speed symbol.
The load index is a code for the most weight one tyre may carry, at the speed of its speed symbol and the pressure the standard sets for it: 91 means 615 kg. The speed symbol is the highest speed the tyre is rated for at that load: H means 210 km/h. Both come from the standard tables of ISO 4000 and the ETRTO standards manual, which this tool uses. A replacement should match or exceed the load index and speed symbol on your car’s tyre placard.
XL (Extra Load) and RF (Reinforced) mark a tyre built to carry more, at a higher pressure, than a standard tyre of the same size. A run-flat tyre carries its maker’s marking, such as RFT, ROF, SSR or ZP: it can be driven a limited distance at reduced speed after losing pressure, as its maker specifies. M+S (mud and snow) is the maker’s own marking for a tread pattern; unlike the three-peak mountain snowflake symbol, it involves no snow test. A C after the rim size, as in 195/70R15C, marks a commercial tyre for vans and light trucks.
The DOT date code
Tyres made for sale in the United States must carry a DOT code, and many tyres sold elsewhere have one too. Under US regulation 49 CFR 574.5 its last four digits are the week and year the tyre was made: 2324 means week 23 of 2024. The date may be moulded on one side of the tyre only, so look at both.
Before 2000 the date had three digits, the week and the last digit of the year, so those codes can’t say which decade. A tyre with one is more than 25 years old.
How old is too old
Rubber ages even when a tyre isn’t used and the tread still looks deep. There is no single legal age limit. Tyre makers generally advise an inspection every year once a tyre is five years old and replacement at ten years at most, and many carmakers advise replacing tyres six years after they were made. Heat and strong sun speed the ageing up.
A new tyre can already be a year or more old when it is sold, so check the code before it is fitted.