How to read car tire size

Before you buy a new tire for your car, you need to know its size, as well as other specifications such as tire maintenance and design. If you don't buy a tire designed for your car or one...

Before you buy a new tire for your car, you need to know its size, as well as other specifications such as tire maintenance and design. If you buy a tire that is not designed for your vehicle, or if it is not the same size as the other tires, you will experience steering problems and lose efficiency and performance. Use this guide to understand what all the numbers and letters on your tire sidewall mean.

Part 1 of 4: Determining the Service Type

"Service Type" tells you what type of vehicle the tire is made for. For example, some tires are designed for passenger cars, while others are for larger trucks. The type of service is indicated by a letter preceding the tire size and is marked on the sidewall of the tire.

While the type of service is not an indicator, it does help you find the right tire size for your vehicle. There are differences related to the type of service, such as tread depth and the number of plies used to make the tire, but these numbers are not used in determining the overall tire size.

Step 1. Locate the group of numbers on the side of the tire.. The group of digits represents the tire size, given in a format such as "P215/55R16".

Step 2: Determine the previous tire size letter.. In this example, "P" is the service type indicator.

The letter indicates for which category of vehicles the tire is intended. Here are the possible letters you'll see for the type of tire service:

• P for passenger car
• C for commercial vehicle
• LT for light trucks

• T for temporary tire or spare tire

• Attention: Some tires do not have a maintenance letter. If there is no service type letter, it means the tire is metric. You will most often see this type of tire for European vehicles.

Part 2 of 4: Find the tire section width

The section width is the number that comes immediately after the service type as a three-digit number. The profile width indicates the overall width of the tire when fitted to the appropriately sized wheel. Measured from the widest point of the inner sidewall to the widest point of the outer sidewall. Wider tires generally give more grip, but can be heavier and cause more fuel consumption.

Step 1: Read the first set of numbers after the letter. This will be three digits and is the measure of your tire's width in millimeters.

For example, if the tire size is P215/55R16, tire profile width 215 millimeters.

Part 3 of 4. Determine the tire aspect ratio and sidewall height.

The aspect ratio is the height of the sidewall of an inflated tire in relation to the profile width. Measured in percentage. A higher aspect ratio value indicates a taller sidewall. A tire with a higher aspect ratio, such as "70", provides a smoother ride and less road noise, while a smaller aspect ratio provides better handling and cornering.

Step 1: Find the aspect ratio. This is the two-digit number immediately following the slash, following the section width.

Step 2: Calculate Sidewall Height. If you want to get a sidewall height measurement in millimeters, multiply the section width by the aspect ratio number, then divide by 100.

For example, take a tire size P215/55R16. Multiply 215 (section width) by 55 (aspect ratio). Answer: 11,825.

Divide this number by 100 because the aspect ratio is a percentage and the sidewall height is 118.25mm.

Step 3. Find the next letter right after the second set of numbers.. This describes how the layers on the tire are arranged, but does not indicate the size of the tire.

The vast majority of passenger cars today will have an "R" for this section, signifying that it is a radial tire.

The other type of tire construction, the bias ply, is obsolete and typically results in excessive wear and increased fuel consumption.

Part 4 of 4: Determining Tire and Wheel Diameter

One of the most important metrics on your tire is the diameter. The tire you choose should fit the rim bead of your vehicle. If the tire bead is too small, you will not be able to fit the tire onto the rim and seal it. If the inside diameter of the tire is too large, it won't fit snugly on the rim and you won't be able to inflate it.

Step 1: Find the number after the aspect ratio. To find the tire and wheel diameter, look at the last number in the size sequence.

This is usually a two-digit number, but some larger sizes may include a decimal point, such as "21.5".

This number will let you know what tire size will be needed to fit the wheels on the car.

Tire and wheel diameters are measured in inches.

For example in P215/55R16, tire and wheel diameter is 16 inches.

Choosing the right tires can change your driving experience. Replacing a tire with the right performance tire is important if you want to ensure fit, performance and safety.

Sometimes, excessive wear on one tire can be a sign of another problem with another vehicle system, such as a problem with the brakes or suspension system. If you want to check your systems before changing a tire, an AvtoTachki certified mechanic can check your vehicle's excessive wear problem to make sure all other systems are working properly before changing.