✦Key Facts
- →The main size code (e.g., 215/55R17) tells you width, aspect ratio, and rim diameter
- →The first three digits are the section width in millimeters (215mm)
- →The two digits after the slash are the aspect ratio — sidewall height as a percentage of width (55%)
- →The number at the end (17) is the rim diameter in inches
- →The DOT code last 4 digits show manufacture week and year (e.g., 2223 = week 22 of 2023)
Breaking Down the Main Size Code: 215/55R17
- •215 — Section width in millimeters. The width of the tire measured from sidewall to sidewall when mounted.
- •55 — Aspect ratio. The sidewall height is 55% of the section width (215 × 0.55 = 118mm sidewall height).
- •R — Construction type. R = Radial (virtually all modern passenger tires are radial).
- •17 — Rim diameter in inches. This must match your wheel exactly.
Service Description: Load Index and Speed Rating
After the size code you will see a number and a letter, such as "94V". The number is the load index — a code that represents the maximum weight the tire can support (94 = 670 kg per tire). The letter is the speed rating — the maximum sustained speed the tire is designed for (V = 149 mph / 240 km/h). Never replace a tire with one that has a lower load index or speed rating than the original specification.
The DOT Code: Manufacturer and Age
Every US-market tire has a DOT code starting with "DOT" followed by a series of letters and numbers. The last four digits are the most important: they are the week and year of manufacture. "2223" means the tire was made in week 22 of 2023. The rest of the code identifies the plant and tire line — useful for recalls but not for everyday buying decisions.
Specialty Markings to Know
- •M+S or M&S: Mud and Snow rated — usable in light winter conditions
- •3PMSF (Three Peak Mountain Snowflake): Severe winter service rated
- •ROF, SSR, EMT, RFT: Run-flat tire designations (vary by manufacturer)
- •XL or Extra Load: Reinforced sidewall for higher load capacity
- •P (before size): Passenger car tire specification (US market)
- •LT (before size): Light Truck specification — load range marked separately
Finding the Right Replacement Tire
Your vehicle's door jamb sticker (driver's side door edge) shows the recommended tire size. You can also find it in the owner's manual. When searching for replacements, match all three parts of the size code exactly. Load index and speed rating should match or exceed the original. If you are not sure, our team at any MrGoma location can look up the correct specification for your vehicle.
Frequently Asked Questions
What do the numbers on a tire sidewall mean?
The main size code (e.g., 215/55R17) tells you: 215 = width in mm, 55 = aspect ratio (sidewall height as % of width), R = radial construction, 17 = rim diameter in inches. After the size you see a load index and speed rating (e.g., 94V).
How do I know what size tire I need?
Check the sticker on your driver's side door jamb — it shows the recommended tire size, load index, and speed rating for your vehicle. You can also find this in your owner's manual or by checking the sidewall of your current tires.
What does the R mean in a tire size?
R stands for Radial, which describes the internal construction of the tire. Nearly all modern passenger and light truck tires are radial. You may also see B (Bias-ply) on older tires or specialty applications.
Can I put a different size tire on my car?
Small variations are sometimes acceptable (like going from a 215 to a 225 in width), but major changes affect speedometer accuracy, load capacity, and handling. Always consult with a tire professional before changing tire size.