You’ve deciphered the numbers on your tire and determined what tire size you need, however, understanding your tire markings goes beyond knowing what “fits” on your car. Your tire sidewall can actually tell you much more than your tire size, like your car’s load capacity, handling capabilities at various speeds, mileage, and even traction on different road types. See why your tire sidewall holds the key to a great (and safe) driving experience!
Your tire sidewall gives you info about your...
Load Carrying Capacity
Different tires can carry different amounts of weight. This is where load capacity comes in. As you can probably imagine, it’s never a good idea to overload your tires, just like it's never a good idea to overload your backpack or pockets. Something's gotta give! Overloading your tires can cause blowouts or premature wear–meaning you don’t get your money’s worth.
In the number sequence on a tire, the load capacity is listed right after the tire’s diameter. Refer to this load index chart to gauge your load-carrying capacity.
As an example, if your tire has a load index of 95, it can support 1,521 pounds. Multiply that times four (since your vehicle has four tires!) and it can support 6,084 pounds. Do not install tires with a lower load carrying capacity than the factory-installed tires!
Speed Rating
A tire’s speed rating indicates the maximum speed that the tire can safely maintain over time, in a controlled laboratory environment. In short, it’s the fastest speed a tire can handle before it no longer performs as designed. The higher the speed rating, the better control and handling you’ll have at higher speeds.
The speed rating system was developed to help control the safe performance of tires at standardized speeds. A tire’s certified speed rating is given a letter from A to Z, ranging from 5 km/h (3 mph) to above 300 km/h (186 mph).
Use the speed symbol chart to better understand the speed rating for your tires. For example, a speed rating of H means the tires are certified up to 130 miles per hour.
Mileage
To compare the mileage you can get out of certain tires, take a look at their treadwear grade. A treadwear grade is given based on the wear of a tire when tested in controlled conditions. When you’re comparing treadwear grades, always compare within tires of the same brand.
Let’s say you’re looking at two tires in Brand A. If Tire #1 has a treadwear grade of 400 and Tire #2 has a treadwear grade of 200, then Tire #1 should, in theory, last twice as long as Tire #2. Of course, this depends on how you drive, road conditions, and a variety of other factors.
Traction
Tires are given traction grades, ranging from AA to C, that represent that tire’s ability to stop on wet pavement. Tires with a traction grade of A will have better grip and stopping ability than a tire with a traction grade of C.
Got tire sidewall questions?
Get answers at your local Firestone Complete Auto Care. Talk to knowledgeable tire technicians in-store and explore tire sizes and prices online. Calculate your out-the-door price in an instant and stop by today! Our technicians are here to answer all of your tire questions.
