A tire size like 205/55R16 91V lists width in millimeters, sidewall height as a percentage of width, rim diameter in inches, a load index, and a speed rating — read left to right.
That string pressed into your tire’s rubber is a specification sheet, not random code. The sequence runs width, aspect ratio, construction, rim diameter, load index, and speed rating — and the same sidewall carries a separate date stamp telling you how old the tire actually is. Here is how each piece decodes, plus the markings most drivers never notice.
What Do the Numbers on a Tire Sidewall Mean?
Find the largest string on the sidewall, usually near the top, formatted like 205/55R16 91V. Each position answers one question:
- 205 — nominal section width in millimeters, measured sidewall to sidewall.
- 55 — aspect ratio; sidewall height equals 55% of the tire’s width. Lower means shorter, sportier; higher means taller, cushier.
- R — radial construction, standard on virtually every passenger vehicle today.
- 16 — wheel or rim diameter in inches. Must match your wheel exactly; a 16-inch tire will not seat on a 17-inch rim.
- 91 — load index, a numeric code for maximum carrying capacity rather than a direct pound figure.
- V — speed rating, a letter code for the top sustained speed the tire is built to handle.
Load index and speed rating are performance limits, not suggestions. Dropping either below what your vehicle’s manufacturer specifies is a downgrade you should not make, even if the tire physically fits.
| Sidewall Marking | What It Tells You |
|---|---|
| 205/55R16 91V | The full size code: width, aspect ratio, construction, rim diameter, load index, speed rating |
| DOT | Confirms the tire meets U.S. Department of Transportation and NHTSA compliance standards |
| DOT/TIN last four digits | Manufacture date — first two digits are the week, last two are the year |
| M+S or M/S | Mud and snow marking for winter-weather traction |
| UTQG grades | Treadwear, traction, and temperature ratings on U.S.-market tires |
| Maximum inflation pressure | The ceiling pressure for the tire — not your everyday recommended operating pressure |
| Load range / ply / material | Construction and load-carrying details of the tire’s build |
How Do You Find the Tire’s Manufacture Date?
The manufacture date is almost always the last four digits of the DOT code. The first two give the week of the year, the last two the year. A code ending in 2321 means the tire was built in the 23rd week of 2021.
That matters because the sidewall date reflects when the tire was made, not when you bought it — a tire can sit in a warehouse before reaching a sales floor. The DOT marking itself confirms the tire meets U.S. Department of Transportation and NHTSA labeling standards. The National Highway Traffic Safety Administration publishes the labeling rules behind these markings if you want the full regulatory picture.
What Other Sidewall Markings Should You Check?
M+S or M/S indicates a mud and snow rating. UTQG grades — treadwear, traction, and temperature — appear on U.S.-market tires and give a relative sense of tread longevity, heat handling, and grip. You will also find load range, ply, and material callouts describing construction, plus a maximum inflation pressure figure.
Read that inflation number carefully: it is the greatest pressure the tire should ever hold, not the pressure you should run day to day. Your vehicle’s recommended pressure lives on the driver’s door jamb placard or in the owner’s manual, and it is usually far lower. If you are weighing budget replacements, a roundup of the best affordable tires tested for value can narrow the field before you start comparing sidewall codes.
Does the Size Code Confirm the Tire Fits Your Car?
No — matching the size string gets you the correct physical dimensions, but load index, speed rating, and your vehicle’s required fitment all have to line up too. The safest move is to match the code printed on the tire your car came with, or read the fitment spec off the door jamb placard, rather than eyeballing a tire that looks close.
Once you can decode a sidewall, ordering a replacement stops being a guessing game. Read the string left to right, check the DOT date before you commit, and never downgrade the load index or speed rating below what your car calls for.
FAQs
What does the number after the rim size mean?
That number is the load index, a code representing the tire’s maximum carrying capacity — not a direct pound measurement. It pairs with the letter that follows it, which is the speed rating. Both are performance limits, and neither should be set below your vehicle manufacturer’s requirement.
Is the tire’s sidewall date the same as when I bought it?
No. The last four digits of the DOT code reflect the week and year the tire was manufactured, which can be well before the purchase date. The tire may have spent time in storage or on a shelf before it reached you, so the stamp measures rubber age, not transaction date.
Is maximum inflation pressure the same as my recommended tire pressure?
No — they serve different purposes. The sidewall figure is the absolute ceiling the tire should ever hold. Your normal operating pressure is set by the vehicle manufacturer for your specific car and load, and it usually sits lower. Check the door jamb placard or owner’s manual for the correct everyday number.
References & Sources
- Michelin. “Tire Markings Explained” Explains the size string breakdown and common sidewall symbols.
- National Highway Traffic Safety Administration. “Tire Labeling” Covers DOT compliance markings and the TIN date code rules.
- Tire Industry Association. “Reading a Tire Sidewall” Consumer guide to interpreting sidewall markings correctly.