What Does 315 Mean on a Tire?
Have you ever looked at the sidewall of your car or truck tires and wondered what all those numbers mean? If you’ve seen a tire with “315” in the size, you may be curious what that number indicates.
In short, the “315” refers to the width of the tire in millimeters. However, there’s more to a tire size than just one number. Let’s take a closer look at what tire size numbers mean and why they matter.
Meaning of “315”
In a tire size with “315”, such as 315/70R17, the “315” specifically refers to the width of the tire from sidewall to sidewall in millimeters when mounted and measured on the specified wheel rim. So a tire with a size of 315/70R17 has a width of 315mm, or about 12.4 inches.
The larger the first number in a tire size, the wider the tire will be. Wider tires provide more contact area with the road, which can improve traction and handling, especially in high-performance applications. However, wider tires also tend to have a shorter sidewall height, which can make for a firmer ride.
Understanding Tire Size
While the “315” refers to the tire width, the other numbers in a tire size are also important:
- The “70” after the slash mark in a 315/70R17 tire means the height of the sidewall is 70% of the tire’s width. This is known as the aspect ratio. A lower number means a shorter sidewall.
- The “R” stands for radial, referring to the tire’s construction. Nearly all modern tires are radial tires.
- The “17” is the diameter of the wheel rim the tire is designed to fit, in inches.
So in a 315/70R17 tire, we have a tire that is 315mm wide, has a sidewall height that is 70% of the width, has a radial construction, and fits a 17″ wheel.
Why Tire Sizes Matter
Choosing the right tire size is crucial for your vehicle’s performance, safety, and fuel efficiency. Tires that are too small may not provide enough load capacity, while tires that are too large may rub against your vehicle’s suspension or bodywork.
When replacing tires, it’s generally best to stick with the size recommended by your vehicle’s manufacturer. This information can usually be found in your owner’s manual or on a placard inside your driver’s side door jamb.
Of course, some people choose to deviate from the standard sizes for performance or aesthetic reasons, but it’s important to understand how changing tire sizes can affect your vehicle’s handling and safety.
Conclusion
So now when you see a “315” on a tire sidewall, you’ll know it refers to the tire’s width in millimeters. By understanding what tire size numbers mean, you can make more informed choices when buying new tires and ensure your vehicle performs at its best.
Whether you’re looking for better fuel economy, improved handling, or just a smoother ride, choosing the right tire size is an important part of vehicle maintenance.
Meet Caitlin McCormack, a Tire Size Expert and Blogger Passionate About Everything Related to Tires. With Years of Experience in the Tire Industry, Caitlin Has Become an Expert in Tire Sizes and Their Impact on Vehicle Performance.