How to Read Tire Size

Having the right tire size is crucial for your vehicle’s safety, performance, and comfort. However, understanding the numbers and letters on your tire’s sidewall can be confusing if you’re not familiar with what each one means.

Knowing how to read tire size will help you to make an informed decision when purchasing new tires. Whether you’re looking to replace worn-out tires or upgrade them for better performance, understanding tire dimensions will ensure you get the best fit for your vehicle. In this guide from Blain’s Farm & Fleet, we’ll break down each part of the tire size code, explain its significance, and offer tips on how to select the right tires.

Where to Find Your Tire Size

When you’re looking for new tires, the most important thing to know is your tire size. There are a few places you can look to find the tire size that is compatible with your vehicle. You can look for your tire size:

1. In your vehicle’s owner’s manual.
2. On a sticker that’s often located inside the driver-side door jamb, glove compartment, or fuel door.
3. If you see multiple sizes listed, it’s best to look on the tire itself (see below).

How to Read Your Current Tire Size

Look for the alphanumeric code on the sidewall of your current tires. It will be similar to the example above.

Tire sizes are typically represented by a combination of numbers and letters that might look confusing at first glance. Here’s a breakdown of what each part of a tire size means, using the example above.

Treadwear

The treadwear rating measures the tire’s durability. It does not measure the projected tread life. Tread life can be affected by driving habits, driving surfaces, and a number of other factors. Individual tire manufacturers determine the treadwear rating.

The ratings can vary between tire brands. So when you’re comparing tires, it’s important to compare ratings within the same brand. The higher the treadwear rating, the longer the tire tread will last. In our example, the 440 treadwear rating indicates the tread would last twice as long as a tire with a rating of 220.

Traction

The tire’s traction rating measures the tire’s ability to stop on a wet, straight surface in controlled conditions. The traction rating doesn’t include the tire’s traction on ice or snow. It also doesn’t include the tire’s cornering ability. Traction can be graded by AA, A, B, or C, with AA being the highest traction grade.

Temperature

Temperature rating measures the tire’s resistance to generated heat at the recommended tire pressure, in normal driving conditions. Temperature grade ranges from A to C. A is the highest rating a tire can have, making it the most resistant to generated heat.

Tire Class

The first character on the sidewall markings is the tire’s class. “P” means that the tire is a passenger car tire. “LT” means the tire is a light truck tire. “ST” means special trailer.

If there is no letter before the tire size, it means it is a European metric tire.

Width

The next section of the tire is the width. The tire’s width is measured in millimeters. Wider tires can provide better grip but may affect fuel efficiency.

Ratio

The ratio number is the height of the sidewall from the wheel to the top of the tire tread. The height is a percentage of the width. In our example, the ratio is 55% of the 205 mm width, equaling 112.75. A lower aspect ratio often means better handling but can result in a harsher ride.

R for Radial

Most modern tires are radial, indicated by the “R.” The radial tires construction type is standard for passenger vehicles.

Rim Size

Rim size is the next character on the sidewall markings. The size of the tire’s rim is measured in inches. Our example shows a 16-inch diameter. That means you need to pair it with 16-inch rims.

Load Index

The next figure on your sidewall is the load index. The tire’s load index measures the maximum amount your tires can safely carry. Your tire’s load index will range from 0 to 279. Each index rating represents a different weight, measured in pounds.

In our example, the tire has a load index of 89. A load index of 89 indicates that 1,279 pounds is the maximum amount the car can carry safely. Maintaining the correct load capacity is very important for your tires.

Load range identifies the load and inflation limits of a tire. Tire load ranges are indicated by letters B, C, D, E, or F. The load pressure is measured in PSI.

• B = 35 PSI
• C = 50 PSI
• D = 65 PSI
• E = 80 PSI
• F = 95 PSI

Speed Rating

Speed rating is determined by the U.S. Government. Tires are tested to see if they meet the minimum standards for reaching and keeping a specific speed limit. Different letters designate specific top speed ratings for each tire.

• Q = 99 mph
• S = 112 mph
• T = 118 mph
• U = 124 mph
• H = 130 mph
• V = up to 149 mph
• Z = 149 mph and above
• W = 168 mph
• Y = 186 mph

Why Tire Size Matters

• Safety: Using an incorrect tire size can impact your vehicle’s handling, braking, and overall safety. Always adhere to the manufacturer’s recommended tire size.
• Performance: Proper tire size ensures optimal performance, including acceleration, cornering, and fuel efficiency.
• Comfort: The right tire size will make your ride more comfortable. Tires that are too large or too small can make the ride rougher.

When in doubt, consult with a tire specialist to ensure you’re making the right tire choice. The experts at our Automotive Service Centers would be happy to help.

Once you know your tire size, you can use our tire lookup feature to find tires online. You can also find quality tires at your local Blain’s Farm & Fleet tire shop. At Blain’s Farm & Fleet, you don’t have to settle for cheap tires. We offer quality brands you can trust, such as Goodyear, Michelin, and Cooper Tire.

For more how-to guides like this one, check out our other Tires articles.