The Fundamentals of Decoding Tire Sizes: Converting 285/70R17 to Inches

Understanding the numbers and letters on your tire’s sidewall can be a real puzzle, but it is essential for taking care of your vehicle. We’re here to help you decode those cryptic markings to understand tire sizes better. Converting 285/70R17 to inches is difficult now. Soon, you’ll be able to get accurate measurements for your vehicle’s tires and ensure that they are ideally suited for your driving needs.

Converting 285/70R17 to Inches

Metric vs. Inch Tire Sizes

Understanding the differences between these measuring systems is essential when selecting the right tires for your vehicle.

Metric Tire Sizing: This system uses millimeters to express the width and aspect ratio, like in the 285/70R17 tire. It’s a more precise system widely used in modern vehicles.

Inch-Based Tire Sizing: Historically, tires were sized using inches, so you might still encounter inch-based tire sizes on older vehicles or specialty tires. In this system, the width, aspect ratio, and rim diameter are all measured in inches, like 33×12.5R15. This system is becoming less common but is still relevant in specific contexts.

 Metric Tire SizesInch Tire Sizes
PrecisionMore preciseLess precise
UnderstandabilityEasier to understandMore complex to understand
FlexibilityMore flexibleLess flexible

Understanding the 285/70R17 Tire Size

The First Number: 285

The initial number in the code signifies the tire’s width in millimeters. For instance, in a 285/70R17 tire, it’s 285 millimeters wide. Wider tires often enhance road performance, offering better traction and stability, albeit potentially reducing fuel efficiency and raising road noise.

The Second Number: 70

The second number is the aspect ratio, showing the tire’s profile as a percentage of its width. 70 indicates that the sidewall height is 70 percent of the tire’s 285-millimeter width.

The aspect ratio is crucial because it directly impacts the tire’s ability to absorb shocks and provide a comfortable ride. Tires with a higher aspect ratio, like this one, tend to have taller sidewalls, offering more cushioning and comfort. Tires with lower aspect rations often grace high-performance vehicles. They provide a sportier feel and sharper handling due to their shorter sidewalls.

The Letter: R

In tire codes, the letter R indicates radial construction. This design features fabric cords that run across the tire from bead to bead, with extra layers running perpendicularly. This construction is typical; its longer tread life, better fuel efficiency, and improved handling make it a popular choice.

The Last Number: 17

This number indicates the wheel or rim diameter in inches, ensuring proper tire fit. A 17-inch diameter fits this example. The right rim size maintains tire integrity and vehicle performance. Larger wheels offer better handling but often increase costs.

Selecting an appropriate rim size in line with tire specifications is crucial. Mismatched rim sizes can lead to fitment, handling, and safety issues. Those who know how to read the different markings on a tire hold an advantage in making informed selections. This knowledge ultimately influences vehicle performance and ride comfort.

Converting 285/70R17 to Inches

Convert the Width (285) to Inches

Width (in inches) = Width (in millimeters) / 25.4

Substituting 285 mm into the formula:

Width (in inches) = 285 mm / 25.4 ≈ 11.22 inches

11.2 inches tire

Therefore, the width of the 285/70R17 tires is approximately 11.22 inches.

Calculate the Sidewall Height (70) in Inches

First, you calculate the sidewall height in millimeters, and then you convert that to inches.

Step 1: Calculate sidewall height in millimeters

Sidewall Height (in millimeters) = Width (in millimeters) * Aspect Ratio (as a decimal)

Sidewall Height (in millimeters) = 285 mm * 0.70 = 199.5 mm

Step 2: Convert sidewall height to inches

Sidewall Height (in inches) = Sidewall Height (in millimeters) / 25.4

Sidewall Height (in inches) = 199.5 mm / 25.4 ≈ 7.85 inches

Therefore, the sidewall height of the 285/70R17 tire is approximately 7.9 inches.

Determining the Rim Size (17) in Inches

The rim size is already provided in inches as ’17.’ There’s no need for any additional conversion in this case. The tire is designed to fit a 17-inch rim.


Understanding tire sizes is crucial for optimal vehicle performance. By choosing the right size, you ensure a safer, more comfortable drive. We hope our guide on converting tire sizes helps you make informed decisions and enjoy your rides with confidence. Decoding sizes is the key to better tire knowledge and more thrilling drives.

Are you looking to learn more tips and tricks? We’ve got you covered in our secrets section.

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