The Right Way To Read Tire Sizes

by pps-DUEditor

If, like many people, you don’t know what all the letters and numbers mean on your tire’s sidewall, you’ve come to the right place. Continue reading to find out which numbers are indicators of tire size, type, and performance.

Tire Type

The “P”, which you will find at the start of the marking, shows that your wheels are P-Metric tires, that are made for passenger vehicles in the United States. If there are no letters at the beginning, the tire follows the Euro metric, which may have different load capacities. The letters “LT,” either at the beginning or the end of the tire size, tell us that the tire was designed for light trucks and may require higher inflation pressures than passenger tires. Remember to check this at least once a month.

Speed Rating

This indicates the maximum speed your tire can handle. Speed ratings are usually matched to the top speed capability of the vehicle. All tire manufacturers recommend checking the speed rating of tires and not exceeding these limits to avoid accidents.

Tire Width

This refers to the width of the tire measured in millimeters from sidewall to sidewall.

DOT Symbol

If you see the letters “DOT” on the sidewall, this tells you that the tire complies with all applicable Federal Motor Vehicle Safety Standards in America.


If you see the letter “R” in tire size, remember it stands for Radial, which means the layers run radially across the tire.

Aspect Ratio

This refers to the ratio of the width of the cross-section of the tire to its height. The two-digit number, which you will find after the slash mark, is the aspect ratio. A bigger ratio means bigger tire sidewalls.

Load Index

This indicates the maximum load the tire will support if it is properly inflated. Usually, you will see both pounds and kilograms mentioned on the sidewall.

Wheel Diameter

This refers to the size of the wheel measured from end to end. It is meant to tell us what size of tire is needed for a good fit. E.g., a size P215/65 R18 tire is made for a wheel with an 18″ diameter.

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