What does 265/70R17 mean?

265 is the section width in millimeters, 70 is the sidewall height as a percentage of that width, R means radial construction, and 17 is the wheel diameter in inches. Together they give a tire 185.5 mm of sidewall and 31.61 inches of overall height.

What does the letter before the size mean?

It is the service type. P is P-metric, designed for passenger cars. LT is light truck, built for higher inflation pressures and heavier loads. ST is special trailer. No letter at all usually means a Euro-metric tire, which is rated slightly differently from a P-metric of the same size.

What is the load index and speed rating?

The two characters after the size, such as 112S. The number is a load index that maps to a maximum weight per tire — 112 is 2,469 lb. The letter is the maximum sustained speed the tire is rated for; S is 112 mph, H is 130, Y is 186.

How do you read the tire date code?

The last four digits of the DOT code on the sidewall. The first two are the week and the last two are the year, so 3624 means the 36th week of 2024. Only one sidewall carries the full code, so if you cannot find it, check the other side.

What does the R in a tire size mean?

Radial construction — the body plies run at 90 degrees to the direction of travel. A D means diagonal, or bias-ply, which is now rare outside trailers and classics. A B means belted bias.

Reading the sidewall

Tire Size Meaning

A tire size is four separate facts printed as one string, in two different unit systems, with the most useful number — how tall the tire actually is — left out entirely. Here is what every character of LT265/70R17 112S stands for, and how to get the missing height back.

LT265/70R17 112S, character by character

Every component of the tire size code LT265/70R17 112S
Code	Means	In practice
LT	Service type	Light truck. Built for higher pressures and heavier loads than a P-metric tire of the same size. P means passenger, ST special trailer, and no letter means Euro-metric.
265	Section width	The widest point of the tire, sidewall to sidewall, in millimeters — measured on the size's specified measuring rim, not on whatever wheel it happens to be fitted to.
70	Aspect ratio	Sidewall height as a percentage of section width. 70% of 265 mm is 185.5 mm. This is the number that hides the tire's actual height.
R	Construction	Radial. The body plies run across the tire rather than diagonally. D is bias-ply, B is belted bias.
17	Wheel diameter	The wheel the tire mounts on, in inches. Still imperial even on an otherwise metric code.
112	Load index	Maximum load per tire at full inflation. 112 is 2,469 lb. It is an index, not a weight — the number has to be looked up.
S	Speed rating	Maximum sustained speed. S is 112 mph, T is 118, H is 130, V is 149, W is 168, Y is 186.

Why is the tire's height not on the tire?

Because the code was designed to describe how a tire is built, not how big it is. The aspect ratio is a manufacturing proportion — it tells the factory the relationship between the sidewall and the tread. Overall diameter is a consequence of that proportion, and it depends on the wheel, so it cannot be printed on a tire that might be mounted on more than one.

For LT265/70R17, the height works out at 31.61″: the sidewall is 265 × 0.70 = 185.5 mm, the wheel is 17 × 25.4 = 431.8 mm, and the wheel sits between two sidewalls. The tire size calculator does this for any code.

What about sizes written in inches?

Flotation sizes — 33x12.50R15 — solve exactly this problem by stating overall diameter first and section width second, both in inches. 33 inches tall, 12.50 inches wide, radial, 15 inch wheel. Nothing has to be derived.

The trade is granularity. Flotation heights step in whole inches — 31, 32, 33, 35, 37 — and widths step in whole inches offset by a half: 9.50, 10.50, 11.50, 12.50. That is a far coarser grid than the metric code, and it is mostly confined to light-truck and off-road fitments in North America. Converting between the two notations is covered on the metric to inch conversion page.

The markings that are not the size

The size is one line among many. The DOT code ends in four digits giving the week and year of manufacture — 3624 is the 36th week of 2024. Treadwear, traction and temperature grades appear as a UTQG triple. Maximum inflation pressure is stamped near the bead, and it is a ceiling for the tire, not a recommendation for your vehicle.

The pressure on the sidewall is not your pressure

The figure moulded into the tire is the maximum the casing is rated for. The pressure you should actually run is on the placard in the driver's door jamb, and it is usually far lower.

Common questions about tire size meaning

What does 265/70R17 mean?: 265 is the section width in millimeters, 70 is the sidewall height as a percentage of that width, R means radial construction, and 17 is the wheel diameter in inches. Together they give a tire 185.5 mm of sidewall and 31.61 inches of overall height.
What does the letter before the size mean?: It is the service type. P is P-metric, designed for passenger cars. LT is light truck, built for higher inflation pressures and heavier loads. ST is special trailer. No letter at all usually means a Euro-metric tire, which is rated slightly differently from a P-metric of the same size.
What is the load index and speed rating?: The two characters after the size, such as 112S. The number is a load index that maps to a maximum weight per tire — 112 is 2,469 lb. The letter is the maximum sustained speed the tire is rated for; S is 112 mph, H is 130, Y is 186.
How do you read the tire date code?: The last four digits of the DOT code on the sidewall. The first two are the week and the last two are the year, so 3624 means the 36th week of 2024. Only one sidewall carries the full code, so if you cannot find it, check the other side.
What does the R in a tire size mean?: Radial construction — the body plies run at 90 degrees to the direction of travel. A D means diagonal, or bias-ply, which is now rare outside trailers and classics. A B means belted bias.