How to Read a Tire Sidewall: Size, Load Index, Speed Rating

Start with the size your vehicle calls for

Every tire has its size molded into the sidewall, usually as the biggest string of numbers, such as P225/65R17 102H. You can read it off your current tires, but check it against the Tire and Loading Information placard, which on most vehicles is on the driver’s side door jamb. Your owner’s manual lists it too.

Your current tires may not be the original size if a previous owner or a shop changed them. The placard shows the size the vehicle was designed around, plus the recommended cold inflation pressure. If the two don’t match, ask a certified tire shop before you buy.

Decoding a passenger tire: P225/65R17 102H

1. P is the tire type: P-metric, a passenger tire built to US standards. LT means light truck. No letter at all (225/65R17) means a Euro-metric size, which shares the same basic dimensions but can have a different load capacity, so compare the load index.
2. 225 is the section width in millimeters, measured from sidewall to sidewall.
3. 65 is the aspect ratio. The sidewall is 65% as tall as the tire is wide. Here that works out to about 146 mm, or roughly 5.8 inches. A lower number means a shorter sidewall; a higher number means a taller one.
4. R means radial construction, which is what nearly all car and light truck tires use today.
5. 17 is the wheel (rim) diameter in inches. This has to match your wheel exactly.
6. 102 is the load index. It’s a code, not a weight. 102 means each tire can carry up to 1,874 lbs when properly inflated.
7. H is the speed rating. H means the tire can carry its rated load at up to 130 mph under test conditions. It describes what the tire can handle, not how fast you should drive.

Some passenger tires also show XL (extra load) or “Reinforced” near the size. An XL tire can carry more weight than a standard-load tire of the same size when it’s inflated to a higher pressure. If your placard lists an XL tire, stick with XL so you don’t end up with less load capacity than your vehicle needs.

Decoding a light truck tire: LT275/70R18 125/122S

LT sizes follow the same pattern. LT275/70R18 is a light truck tire, 275 mm wide, with a sidewall 70% as tall as the width, radial construction, for an 18-inch wheel.

The difference is the pair of load numbers. The first (125) is the load index when the tire runs singly, the way most pickups and SUVs are set up: up to 3,638 lbs per tire. The second (122) applies in a dual setup, with two tires side by side like the back of a dually truck: up to 3,307 lbs per tire. The S means 112 mph.

LT tires also carry a load range letter, often printed as “Load Range E” or “LRE.” Common load ranges run from B to F, and you’ll often see C, D or E. Load ranges replaced the old ply-count system, so you’ll still hear them described by ply rating:

• Load Range C: 6-ply rating
• Load Range D: 8-ply rating
• Load Range E: 10-ply rating
• Load Range F: 12-ply rating

The ply rating describes strength, not an actual count of layers inside the tire. A higher load range can carry more weight, but only at the higher inflation pressure it’s built around. Buy the type and load range your placard lists, and run the placard pressure, not the maximum printed on the sidewall.

Quick reference: load index and speed rating

Here are the common codes in one place. Load figures are the maximum per tire at the proper inflation pressure. The two halves of the table are separate lists: a load index isn’t tied to the speed rating on the same row.

On some high-performance tires you’ll also see ZR inside the size, which marks a tire built for speeds above 149 mph.

Two rules for replacements: don’t go below the load index your vehicle specifies, or below its speed rating unless your owner’s manual allows it. A lower speed rating lowers the safe top speed of the whole vehicle to that tire’s rating. Winter tires are the common exception. Many carry lower speed ratings, and US tire industry guidance says that is generally acceptable as long as you keep your speed within the winter tire’s rating. Check your owner’s manual for any limits.

The DOT code: when your tire was made

Look for the letters DOT followed by 8 to 13 letters and numbers. This is the Tire Identification Number. It includes codes for the plant where the tire was made and for the tire size, and it ends with a four-digit date code.

Read those last four digits as week and year. 3625 means the 36th week of 2025, and 0124 means the first week of 2024. Tires made before 2000 used a three-digit code, so if you see only three digits, the tire is more than 25 years old.

Can’t find the date? Federal rules require the full code, including the date, on only one sidewall. The other side may show a shorter version without the date, so check the inner sidewall with a flashlight.

Tire and vehicle makers publish their own guidance on tire age, so check your owner’s manual and have older tires inspected by a tire professional.

Other markings: UTQG, M+S, the snowflake and max pressure

UTQG grades

Most passenger tires show three Uniform Tire Quality Grading marks, such as “Treadwear 500, Traction A, Temperature A.”

• Treadwear is a comparison number from a government test course. A tire graded 400 would wear twice as well on that course as one graded 200. Real-world wear depends on how and where you drive, so treat it as a rough comparison, not a mileage promise.
• Traction (AA, A, B or C, from best to lowest) is based on straight-line braking on wet pavement. It doesn’t measure cornering, hydroplaning or snow grip.
• Temperature (A, B or C) shows how well the tire resists heat buildup. A is the highest grade.

UTQG covers passenger car tires. Deep-tread winter tires, temporary spares and LT tires aren’t required to carry these grades, so a missing grade on those isn’t a red flag.

M+S and the three-peak mountain snowflake

M+S (mud and snow) is based on the manufacturer’s own criteria and doesn’t require a standardized winter test. The three-peak mountain snowflake symbol means the tire met a standardized snow traction test. If you drive in real winter conditions, look for the snowflake. You’ll find it on dedicated winter tires and on some all-weather designs.

Maximum inflation pressure

The “Max. Press.” figure is the most air pressure the tire is built to hold. It is not the pressure you should run. Use the pressure on your door-jamb placard, checked when the tires are cold.

Using your tire size to shop on Sansujyuku

Once you know your size, shopping is quick:

1. Use the Shop by Tire Size tool on our homepage and pick the width, aspect ratio and rim diameter. For P225/65R17, that’s 225, 65 and 17. You can also use Shop by Vehicle to search by year, make and model.
2. Or browse by vehicle type: passenger car tires, SUV and crossover tires and light truck tires. If you want one set for most of the year, start with our all-season tires.
3. On each product, confirm the full size matches, and that the load index, speed rating and (for LT tires) load range meet or beat what your placard lists.
4. At checkout, you can ship tires straight to a local installer. Enter the shop’s address as the shipping address and the shop’s name in the Company name field. Call the shop first so they know the tires are coming.

Shipping is free on orders to the contiguous US (the lower 48 states plus Washington, DC). Orders are processed in 1–2 business days (Monday to Friday), and delivery usually takes 2–3 business days after shipping; both are estimates. Tires ship via UPS or FedEx, with tracking emailed when your order ships. See our shipping policy for details, and if you have a question about an order, contact us.