How to Measure Tire Rim Size

How to Measure Tire Rim Size

During your vehicle’s lifespan, it is inevitable that you will need to replace your tires. When this time comes, it is essential to be sure you are purchasing the correct size tires. But how do you know what size tires you need?

To figure out what tires to buy, you will need to know how to measure tire rim size. The diameter, width, offset, and backspacing measurements are all crucial for selecting new tires. 

In this article, we will provide a step-by-step guide for measuring tire rim size so that you can get the perfect fit.

Measuring the Diameter

Getting the right sized tires is critical for ensuring your vehicle can run safely and efficiently. The first step in how to measure tire rim size is by accurately recording the tire rim’s diameter and width. 

how to determine rim size for tires
  1. Before getting started, remove the rims from your tire and lay it on a flat, secure working surface with the spokes and center facing up. 
  2. Extend a measuring tape or long ruler across the top of the metal, bisecting the center. With this placement of the tape, record the distance between the outer edges of each of the rim’s lips to find the outer diameter’s measurement.
  3. Next, measure the distance from the piece’s outer lip to the barrel. The barrel is the wide, flat piece in the middle of the rim, where the wheel should sit. 
  4. Take the measurement from Step 3 and subtract it from the number you got for the outer diameter. You will need to do this two times. This is to account for the additional width of the lip on each side. The number you get after this will be the actual diameter.

Measuring the Rim’s Width

 how to measure a tire rim

The next step in how to measure tire rim size is finding the width. The width measurement will determine what size tires can safely fit your vehicle without impacting the vehicle’s performance. 

Pro Tip: When selecting a tire, be sure that you choose one that is no more than 1/2 inch (or 1.3 cm) smaller or larger than your rim’s width, as this can impose a significant safety hazard. 

  1. Turn the rim onto its side so that it is sitting in the same orientation it would to attach to the vehicle. To help prevent it from rolling while you work, you can brace it with shims or a folded towel. 
  2. Stretch your measuring tape between the metal outer lips and record the distance between them. This distance is the width of your rims. 

How to Determine Offset and Backspacing

 how to measure rim size without tire

As important as how to measure tire rim size is how to determine the offset and backspacing. Your vehicle’s offset and backspacing measurements are necessary to calculate the brake clearance accurately. 

Backspacing refers to the amount of space available behind your tire’s mounting face. The mounting face is the center backside of the part where you’ll find the bolt pattern. The wheel’s offset measures the distance between the center of the wheel well to the backside of the rim’s center. 

Finding your wheel’s offset and backspacing measurements can require a bit of math. When looking for these measurements, be sure to have some paper on hand to make things easier. 

  1. Begin by measuring the wheel’s width, i.e., the measurement between each of the outer lips of the tire’s rims. Once you have this number, divide it by two to find where the true center is.
  2. Place the metal flat on a surface with the front of it facing downward. Suspend a straightedge, measuring tape, or flat board across the width of the piece. Then measure the distance from the mounting face to the suspended straightedge. This is your backspacing measurement.
  3. Subtract the number of your center measurement from the backspacing measurement to determine your offset. If this number is positive, you have a positive offset. And if negative, you have a negative offset. If there is zero offset, that means the backside of the mounting face is at the center.

Positive offsets are the most common in modern vehicles. This is because it allows for a larger space around the brakes, which offers more stability. If you have a vintage vehicle, you are more likely to find a negative offset. 

The Bottom Line

If you are preparing to replace your vehicle’s tires, you may have wondered how to measure tire rim size to find the right-sized tires. Luckily, it is an easy process that you can manage in just a few steps. Be sure to remove your rims from the tire to ensure you are getting accurate measurements. 

Did you find our guide helpful? Then consider checking other recommended readings:

How To Read Trailer Tire Sizes
How To Convert Tire Size To Inches
How Do You Measure Tire Size
How To Find Out Tire Size
How To Find Tire Diameter