Breaking Down Tire Size Numbers

Tire sizes printed on the sidewall, such as 265/70R17, follow a standardized format that communicates several important measurements about the tire’s dimensions and construction.

What Each Number and Letter Means

The First Number (265)

This represents the tire’s width in millimeters, measured from sidewall to sidewall. A higher number indicates a wider tire.

The Second Number (70)

This is the aspect ratio, representing the tire’s sidewall height as a percentage of its width. A 70 means the sidewall height is 70 percent of the tire’s width.

The Letter (R)

This indicates the tire’s construction type, with R standing for radial, the most common construction method used in modern tires.

The Final Number (17)

This represents the wheel diameter in inches that the tire is designed to fit.

Why Tire Size Matters

Using the correct tire size ensures accurate speedometer readings, proper handling characteristics, adequate ground clearance, and compatibility with your vehicle’s suspension and braking systems as designed by the manufacturer.

Additional Markings on Tires

Beyond the core size, tires often include a load index and speed rating, which indicate the maximum weight the tire can safely carry and the maximum speed it’s rated for under optimal conditions.

Where to Find Your Truck’s Correct Tire Size

Your vehicle’s recommended tire size is typically listed on a sticker inside the driver’s door jamb, in the owner’s manual, or on the existing tire’s sidewall if it’s the factory-specified size.

Frequently Asked Questions

Can I change my tire size from the factory specification?

Some deviation is possible, particularly for larger all-terrain or off-road tires, but significant changes can affect speedometer accuracy, handling, and may require suspension modifications.

What happens if I use the wrong tire size?

Using an incorrect tire size can affect handling, ground clearance, speedometer accuracy, and in some cases cause rubbing against suspension components or the vehicle body.

Does tire size affect fuel economy?

Yes, larger or wider tires generally increase rolling resistance and weight, which can reduce fuel economy compared to the manufacturer’s specified size.