Most people read the first group of characters on a sidewall and stop. The groups after it are the ones that determine whether the tire is legal and safe on your vehicle, and they are the ones fitted incorrectly most often.
The size arithmetic is on the tire size conversion page.
The size group
P265/70R17 — five pieces of information:
| Part | Meaning |
|---|---|
| P | Service type. P = passenger, LT = light truck, no letter = Euro-metric |
| 265 | Section width in millimetres |
| 70 | Aspect ratio — sidewall height as a percentage of section width |
| R | Radial construction |
| 17 | Wheel diameter in inches |
The service letter matters more than it looks. LT tires are built for higher loads and run higher pressures, and an LT tire fitted where a P tire belongs rides harder and, more importantly, needs different inflation to carry the same load. Swapping between them is not a like-for-like change.
Tires with no leading letter are Euro-metric, and a Euro-metric tire and a P-metric tire of the same numerical size can have slightly different load capacities at the same pressure.
The service description
Immediately after the size: 115T.
115 is the load index — a coded maximum load per tire. It is not pounds; it is an index into a standard table. Higher is more.
T is the speed rating — the maximum sustained speed the construction is certified for, again a coded letter.
This pair is a safety specification, not a preference. The vehicle's tire placard — usually in the driver's door jamb — states the minimum load index and the speed rating for the vehicle as built, along with the correct inflation pressures. That placard, not the tire currently fitted, is the reference.
The failure mode worth knowing: chasing a wider or cheaper tire in the same nominal size can quietly land you on a lower load index than the vehicle requires. On a loaded vehicle or a tow, that is a genuine hazard. The Tire Industry Association and the vehicle manufacturer are the authorities here.
Load range and ply rating
On light truck tires you will also see Load Range C / D / E or a ply rating.
These indicate the tire's construction strength and the pressure it is designed to run at — an E-rated tire is built for higher inflation and higher load than a C. They are not interchangeable with the load index; they are a separate, coarser classification.
Fitting a higher load range than needed is not free. E-rated tires on a light vehicle ride harshly, because they are stiff enough to carry a load the vehicle does not have, and running them at their maximum pressure on an unloaded vehicle reduces the contact patch.
The date code
Look for DOT followed by a string of characters, ending in four digits — for example 3224.
Those four digits are the manufacturing date: week 32 of 2024. Every tire has one, and it is the only way to know the tire's real age.
Why it matters: rubber ages whether the tire is used or not. A tire that has sat in a warehouse for five years is five years old, regardless of tread depth. Many manufacturers and vehicle makers advise replacement at a given age irrespective of wear, and the ranges commonly cited run from six to ten years. Check the date code on tires you are buying, particularly on a bargain, and on the spare, which is frequently the oldest tire on the vehicle by a decade.
The rest
M+S — mud and snow, a self-certified marking with fairly weak criteria.
Three-peak mountain snowflake — a tested severe snow service rating. This one means something the M+S marking does not, and where winter tires are legally required it is usually this symbol that qualifies.
Treadwear, traction, temperature — the UTQG grades. Treadwear is a comparative index within a manufacturer's own range and is not reliably comparable between brands. Traction (AA to C) and temperature (A to C) are tested grades.
Max load and max pressure — the tire's own structural limits. Neither is a recommendation. The pressure you should run comes from the vehicle placard, not from the sidewall, and this is the single most common misreading of a tire.
Rotation arrow or "outside" — directional tires must run one way; asymmetric tires have a specific outboard face. Fitted wrong, both perform badly in the wet.
What this page does not cover
- Diameter arithmetic and speedometer error are on the main conversion page.
- Load index and speed rating tables — use the vehicle placard and the manufacturer's data rather than a partial table.
- Legal requirements for tread depth, winter tires and load ratings vary by jurisdiction.
- Pressure for a specific load, which comes from the vehicle manufacturer's load-inflation tables.
The size tells you what it measures. The service description tells you whether you may fit it.