Published by Rims & Tires
Compiled & checked by the site's publisher from manufacturer, NHTSA & USTMA data · Updated 2026-07-24
Decoding a tire sidewall is one of those skills that makes buying tires and checking specs a whole lot less confusing. Once you know what the markings mean, you can read a tire like a label and verify exactly what you are getting before it goes on the car.
The size string — the most important part
Example: 225/65R17 or P225/65R17. Every passenger and light truck tire has a size string.
P (or no prefix): "P" means P-metric, designed for passenger vehicles. "LT" means Light Truck — heavier construction, higher load capacity. No prefix is common on European-metric tires.
225: section width in millimeters, measured sidewall to sidewall at the widest point.
65: aspect ratio, the sidewall height as a percentage of the section width. On a 225/65 tire the sidewall is 65% of 225mm, about 146mm tall.
R: radial construction. Nearly every tire on a modern vehicle is radial; bias-ply tires hang on only in a few niche uses.
17: wheel diameter in inches, the rim size the tire fits.
Load index
The load index is a number (usually 2-3 digits, like 91 or 115) that appears after the size string.
Load index 91 = 1356 lbs max per tire. Load index 115 = 2679 lbs per tire. Higher number = heavier load capacity.
Common passenger tire load indexes: 89 (1279 lb), 91 (1356 lb), 94 (1477 lb), 97 (1609 lb), 100 (1764 lb), 103 (1929 lb).
For trucks and SUVs: the door jamb sticker lists the minimum load index required. Never drop below it. This is a structural capacity issue, not just a legal box to check, and a tire that cannot carry the vehicle's weight is a real safety problem.
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Speed rating
A single letter follows the load index: T, H, V, W, Y are the most common on modern vehicles.
T = 118 mph. H = 130 mph. V = 149 mph. W = 168 mph. Y = 186 mph.
The speed rating is the maximum sustained speed the tire can safely handle at its maximum load. Read it as an engineering limit, not a suggestion to go drive that fast.
Going up is fine: an H-rated car can wear V-rated tires with no issue. Going down is not. A vehicle that calls for W should never get T-rated tires.
Performance vehicles often specify W or Y minimum. Most daily drivers specify H or V.
DOT code and manufacture date
Every tire sold in the US carries a DOT code, required by the U.S. Department of Transportation and stamped right on the sidewall after the letters "DOT." The last four digits are the ones that matter: the week and year it was built. "2322" means the 23rd week of 2022.
Tire age matters: most manufacturers recommend replacing tires 6–10 years from manufacture regardless of tread depth. Rubber compounds degrade even when the tire looks fine.
When buying tires, especially "new" tires at a discount shop, check the DOT date. A tire manufactured 4+ years ago may have significant shelf life already consumed.
UTQG ratings
UTQG (Uniform Tire Quality Grading) is a government-mandated rating system printed on the sidewall: three numbers like 500 A A or 300 A B.
First number, treadwear: tread life relative to a government reference tire. A 400 lasts roughly twice as long as a 200. It is a relative index, not a mileage guarantee.
Second letter, traction: how well the tire stops on wet pavement. AA is the highest, then A, then B, with C the minimum.
Third letter, temperature: heat resistance. A is the highest, then B, then C, the minimum the law allows. Most quality tires rate A.
Frequently asked
Can I put a different size tire on my car?
Minor plus-sizing (same diameter, wider width) is common for aesthetics or performance. Significantly different diameters affect speedometer accuracy, ABS calibration, and traction control — usually within 3% of the original diameter is the guideline. Always verify fitment with the shop.
What does M+S mean on a tire?
M+S (Mud + Snow) means the tread meets a minimum threshold for mud and snow traction. It is a self-designation by the tire manufacturer — not an independent test. It does NOT mean the tire is a true winter tire. Look for the Three-Peak Mountain Snowflake (3PMSF) symbol for independently verified winter performance.
Where do I find the sidewall markings on my tire?
Everything is molded into the outer sidewall, though some tires stamp the DOT date code only on the inner side. If you can't find a marking, roll the car forward a few inches to rotate the tire, or check the other sidewall. A shop can read all of it in a minute if you'd rather not crawl around.
Do I have to match the exact sidewall numbers when I replace a tire?
Match the size string, and meet or beat the load index and speed rating. You can safely go up on speed rating, but never down. When you're mixing brands or you're unsure, have a shop confirm the replacement is a proper match for your vehicle.
Does the sidewall tell me how old the tire is?
Yes. The last four digits of the DOT code are the week and year it was built. That matters most when you're buying so-called new tires at a discount, since rubber ages on the shelf. Check the date before you pay, not after.
Keep reading
Last updated 2026-07-24. General guidance only — confirm specifics with a local shop for your exact vehicle.