Rim Sizes Explained: How to Read Wheel Markings

If you're looking to buy a new set of wheels or tires, you'll need to know how to read wheel markings. Vehicle wheels (AKA rims) are not one-size-fit-all, and they have a lot of measurements that you'll need to consider.

Wheel markings are codes that might tell you the size and load rating of the wheel. These codes are typically stamped on the inside of the wheel, which means you might need to safely remove the entire wheel and tire assembly, so you can read the wheel size. 

Note: If you're simply looking to replace your existing wheels with new ones, you can use Tire Agent's wheel matching technology to find ones that will fit your vehicle. You'll need to know your vehicle's make, model, year, trim level and tire (not wheel) size. 

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Where is your tire size? It's clearly visible on the outside of your tire and on the sticker on the inside of your driver's door. The sizes will look something like this:

The meaning of wheel size can refer to the entire wheel and tire assembly, or it can refer to just the metal rim that houses the tire. You'll see people in the automotive industry use "wheel" to refer to a wheel with a tire or without a tire. For the purposes of educating our readers, we're going to refer to wheels (metal) and tires (rubber compounds) as two separate parts. 

Tire size differs from wheel size, which we explain next. One common question we get is, can you change the size of your rims or tires? This isn't a simple yes or no. We cover tire sizes in a separate post.  

Where to Find Wheel or Rim Size

Wheel manufacturers are not held to the same standards as tire manufacturers. The U.S. government requires tire manufacturers to disclose tire information on the visible portion of the tire, which is referred to as the DOT code. We cover DOT codes in a separate blog post. 

In short, the DOT codes tell consumers where and when tires were made, as well as the tire size. There are three numbers that explain tire size. For example, P205/65R15 means that the tire is 205 mm wide, and the height of the tire is equal to 65% of the tire's width. The last number, 15, refers to the wheel diameter that the tire will fit.

How to Measure Wheel Width

Most experts recommend removing the entire wheel and tire from the vehicle and laying it on a flat surface, so you can safely take measurements. 

To measure the width of the wheel, start at the inside of the lip (the rim) and go to the other side. To measure the diameter, start from the outside of the lip and end straight across to the outside of the lip (at the widest part of the tire).

See the illustration below. 

Car Wheel Dimensions Explained

Some manufacturers stamp information on the inside of their wheels, which might include: 

• Maximum load, also known as load index, which is typically expressed in pounds in the United States. So, a max load of 1,000 pounds would be appropriate for a vehicle whose gross axle weight rating (GAWR) is equal to 2,000 pounds, you'd need wheels that at a minimum can carry 1,000 pounds (because there are two wheels per axel). Check your owner's manual to find your vehicle's GAWR.
• Maximum PSI refers to the maximum pounds per square inch of air the tire should hold. That number is also on the placard on the inside of the driver's door.
• Wheel diameter and width might be expressed as a mathematical term, such as 16×7, which means the diameter is 16 inches and the width is 7 inches.
• Wheel offset measurements may be expressed following the letters "ET," as in ET0, which would mean an offset equal to zero. What does ET mean? It's a German phrase, einpresstiefe, which translates to "insertion depth," according to Konig.
• Model number might also be stamped on the wheel, which will be unique to each manufacturer. 
• Manufacturing date is also an optional code that you might find on the wheel. Manufacturing date is not required on wheels, like it is for tires, because the metal has a much, much longer shelf life than the organic compounds that comprise rubber tires!

Understanding Wheel Sizes and Rim Specifications

As much as we like to think that manufacturers' guidelines and government regulations are all about making tire and wheel measurements easy to understand for the average consumer, it isn't. It's nothing like walking into a self-service shoe store and finding shoes that fit your shoe size. Tire and wheel specs are complicated, but once you understand the basics, you easily shop online for tires and wheels.  

If you want to replace your car wheels, and you need help finding the information, reach out to a Tire Agent specialist. We can walk you through finding the best rims to fit your car, truck, SUV or crossover. 

Illustration 18871328 / Car Rims Alexandr Mitiuc | Dreamstime.com