How to Read Tire Sizes
Get a look at your tire sidewall and you’ll see information molded into the rubber, in the form of raised letters and numbers. We’d like to explain to you what that information means, so let’s break it down:
- Load Index – The load index is a reflection of the maximum weight that is safe for a tire to carry. The load index numbers range from 0 to 279; passenger car tires are usually in the 75-105 range. When it’s time to replace your tires you’ll want to pay close attention to those numbers.
- Speed Rating – Speed rating designations are assigned by the U.S. government, and are an indicator of minimum standards for accelerating to and holding a certain specific speed. The higher the speed rating number on a tire, the better a vehicle will ride and handle. Speed rating charts are available on the internet; the designations are in the form of a letter rather than a number.
- DOT – Your tire’s DOT stamp is an indicator that your tire meets the U.S. Department of Transportation’s benchmarks for safety.
- Manufacturer Plant Code – After the DOT stamp, the first two letters are a designation of the tire manufacturer and factory.
This sequence of stamps is followed by a set of letters and numerals that are code for brand characteristics and date of production. Then:
- Treadwear Rating – This is a code for the tire’s durability; not necessarily the projected tread life. Tire manufacturers devise this rating for warranty purposes.
- Traction Rating – Code that indicates a tire’s ability to bring the vehicle to a stop on straight, wet pavement. Traction ratings are AA, A, B and C, with AA as the highest rating.
- Temperature Rating – This rating designates tolerance to high heat and ranges from A to C, with A as the highest rating.
- Maximum Load Limit – Indicator of the tire’s maximum load-carrying capacity at full inflation. Usually this is a much higher number than the load rating, as it’s a reflection of the car’s fully loaded weight as borne by each tire.
- Maximum Air Pressure – Not necessarily recommended inflation pressure; this is the maximum inflation the tire can hold in hot conditions.
You will then see a stamp indicating the actual tire size, such as P215/65R15. This can be read as follows:
P: Passenger Car (or LT for light truck)
215: “Nominal section width,” measured in millimeters, from outside edge to outside edge of tire
65: “Aspect ratio,” meaning sidewall height as a percentage of the total width of the tire
15: Intended rim diameter in inches
For information on how different tire sizes can affect things like gas mileage and rolling resistance, check out our tire size calculator.