How to Read a Tire Sidewall: What Every Number and Letter Means
That string of numbers and letters stamped on your tire sidewall tells you everything about your tire — if you know how to read it. This guide breaks it all down in plain language.
The Basic Format: What Does "225/65R17" Mean?
Nearly every passenger tire follows a standard numbering format. Take 225/65R17 as an example:
- 225 — Tire width in millimeters (from sidewall to sidewall)
- 65 — Aspect ratio: the sidewall height is 65% of the tread width
- R — Radial construction (virtually all modern tires)
- 17 — Wheel diameter in inches
Always replace tires with the exact size listed in your owner's manual or on the driver's door jamb sticker. Using the wrong size can affect speedometer accuracy, fuel economy, and handling.
Load Index and Speed Rating
After the tire size you'll find two more codes — a load index number and a speed rating letter. These are critical for safety.
| Speed Rating | Max Speed | Typical Use |
|---|---|---|
| S | 112 mph | Standard passenger vehicles |
| H | 130 mph | Sedans, minivans, light trucks |
| V | 149 mph | Sport sedans, coupes |
| W | 168 mph | Exotic and performance vehicles |
The DOT Code and Tire Age
The DOT code is stamped on one sidewall and ends in a 4-digit week/year code. For example, "2320" means the tire was manufactured in week 23 of 2020. Tires older than 6 years should be inspected by a professional regardless of tread depth.
Even if tires look fine, the rubber degrades internally over time. Tires more than 10 years old should always be replaced — no exceptions.
UTQG Ratings: Treadwear, Traction, Temperature
The Uniform Tire Quality Grade (UTQG) rating gives you three performance scores molded onto the sidewall. A treadwear rating of 400 means the tire should last twice as long as a tire rated 200. Traction grades (AA, A, B, C) rate wet stopping ability. Temperature grades (A, B, C) rate heat resistance.
Ready to Schedule Service in Newbury Park?
CAL Tire and Auto Repair is here to help. Our ASE-certified technicians serve drivers across Newbury Park, Thousand Oaks, Westlake Village, Camarillo, Agoura Hills, and Simi Valley. Visit us at 1180 Newbury Rd or call to speak with a service advisor.
Frequently Asked Questions
What happens if I install the wrong tire size?
Using a tire that's too wide or tall can cause rubbing against wheel wells, affect speedometer accuracy, and alter handling behavior. Always match the manufacturer's recommended size.
How do I find the right tire size for my vehicle?
Check the sticker on the inside of your driver's door jamb or your owner's manual. Our team at CAL Tire can also look it up instantly at the counter.
Does a higher load index mean a better tire?
Not necessarily — it means the tire can support more weight. You need at least the load index specified for your vehicle, but you don't need more than required for normal passenger cars.