How to measure overall wheel and tire diameter

## Measuring Overall Wheel and Tire Diameter

Calculating the overall diameter of a wheel and tire assembly is essential for ensuring the proper fitment and performance of your vehicle. Here’s a detailed guide on how to measure the overall diameter accurately:

Materials Required:

– Measuring tape or caliper
– Chalk or marking tool

Step-by-Step Instructions:

1. Park Your Vehicle on a Flat Surface:
Park your vehicle on a level surface to ensure accurate measurements.

2. Mark the Top of the Tire:
Using chalk or a marking tool, make a mark on the top of the tire at its widest point.

3. Rotate the Tire One Full Turn:
Rotate the tire one complete revolution until the mark you made is facing down.

4. Mark the Top of the Tire Again:
Make a second mark on the top of the tire at its widest point.

5. Measure the Distance Between Marks:
Use the measuring tape or caliper to measure the distance between the two marks you made. This measurement represents the height of the sidewall.

6. Double the Sidewall Height:
Multiply the sidewall height measurement by two to get the total height of the tire.

7. Add the Rim Diameter:
Measure the diameter of the rim from one edge of the bead seat to the other. Add this measurement to the total tire height.

8. Calculate the Overall Diameter:
The sum of the total tire height and the rim diameter gives you the overall wheel and tire diameter.

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Example Calculation:

– Sidewall height: 5 inches
– Total tire height: 5 x 2 = 10 inches
– Rim diameter: 15 inches
– Overall diameter: 10 + 15 = 25 inches

Additional Tips:

– Always measure the tire when it’s cold to ensure accurate results.
– If you’re using a caliper, place it perpendicular to the tire’s tread to avoid getting skewed measurements.
– For vehicles with aftermarket lift kits or modifications, refer to the manufacturer’s recommendations for the correct overall diameter.
– Consider the impact of tire wear and inflation levels on the overall diameter.

### Measuring Tire Diameter for Replacement:

When selecting replacement tires, it’s crucial to ensure that the new tires have the same overall diameter as the existing ones. Here’s how to measure the tire diameter for replacement:

1. Locate the Tire Size Information:
Check the sidewall of the existing tire to find its size information, typically expressed in the format X/XX RXX.

2. Identify the Diameter Code:
The diameter code is located in the last two numbers of the size information. For example, for a tire with a size of 225/50 R17, the diameter code is 17.

3. Multiply by Two:
Multiply the diameter code by two to get the tire diameter in inches. For the example tire, the diameter is 17 x 2 = 34 inches.

4. Select tires with the same diameter.
When selecting replacement tires, ensure they have the same overall diameter as the old ones to maintain the intended vehicle performance and handling.


Accurately measuring the overall wheel and tire diameter is essential for proper fitment, performance, and safety. By following the steps outlined above, you can easily calculate the overall diameter and ensure that your tires are the correct size for your vehicle. Remember to always refer to the manufacturer’s recommendations and consider the impact of tire wear and inflation levels when making measurements.

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