Dynasty Startup Trade Calculator

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Reviewed by: David Chen, P.Eng. (Professional Engineer)

Last updated: December 2025

Use this **Tire Rim Calculator** to determine the essential dimensions of any metric-sized automotive tire, including the overall diameter, circumference, and sidewall height, based on its standard marking (e.g., 205/55R16).

Tire Rim Calculator

Calculation Result

Sidewall Height (mm)
Overall Diameter (mm)
Overall Circumference (mm)

Tire Rim Calculator Formula

The tire dimensions are calculated using three main formulas:

1. Sidewall Height (H) = W * (A / 100)
2. Overall Diameter (OD) = (2 * H) + (D * 25.4)
3. Overall Circumference (C) = OD * π

Formula Source: Tire Rack Technical Information (Based on standard tire sizing conventions)

Variables

  • Tire Width (W): The width of the tire tread, measured in millimeters (mm). (e.g., the “205” in 205/55R16).
  • Aspect Ratio (A): The height of the tire’s sidewall as a percentage of the width. (e.g., the “55” in 205/55R16).
  • Rim Diameter (D): The diameter of the wheel rim itself, measured in inches. (e.g., the “16” in 205/55R16).
  • 25.4: The conversion factor from inches to millimeters (1 inch = 25.4 mm).
  • π (Pi): Approximately 3.14159.

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What is the Tire Rim Calculator?

The Tire Rim Calculator is a fundamental tool for anyone involved in vehicle maintenance, modification, or purchasing new tires. It takes the three main components of a tire’s metric designation—the width, aspect ratio, and rim diameter—and translates them into physical dimensions like the overall diameter and circumference in millimeters.

Understanding these calculated dimensions is crucial for ensuring proper fitment (preventing fender rubbing), maintaining speedometer accuracy (since the vehicle’s speed is calculated based on tire rotation and circumference), and comparing different tire sizes before a purchase. The calculation ensures that a proposed tire size is compatible with the vehicle’s mechanics and electronics.

How to Calculate Tire Dimensions (Example: 205/55R16)

  1. Determine Sidewall Height: Take the Tire Width (W=205 mm) and multiply it by the Aspect Ratio percentage (A=55%).

    Example: H = 205 mm * (55 / 100) = 112.7 mm

  2. Convert Rim Diameter to mm: Take the Rim Diameter (D=16 inches) and multiply it by the conversion factor (25.4 mm/inch).

    Example: Rim Diameter in mm = 16 * 25.4 = 406.4 mm

  3. Calculate Overall Diameter: Add the two sidewall heights (H * 2) to the converted rim diameter.

    Example: OD = (2 * 112.7 mm) + 406.4 mm = 631.8 mm

  4. Calculate Overall Circumference: Multiply the Overall Diameter (OD) by Pi ($\pi$).

    Example: C = 631.8 mm * 3.14159 = 1985.9 mm

Frequently Asked Questions (FAQ)

What does the “R” in a tire size like 205/55R16 stand for?

The “R” stands for Radial construction, which is the overwhelmingly common type of construction for passenger tires today.

Why is the overall diameter important?

The overall diameter directly affects your vehicle’s gearing and speedometer calibration. A change of more than 3% from the original diameter can cause significant speedometer error and potentially damage anti-lock braking (ABS) systems.

Is Aspect Ratio a measurement in mm or a ratio?

It is a ratio (a percentage). The Aspect Ratio (e.g., 55) means the sidewall height is 55% of the tire’s width (205 mm in the example). It is not a fixed length measurement.

Can this calculator be used for LT (Light Truck) tires?

Yes, as long as the LT tire uses the standard metric sizing format (e.g., 285/75R16), the underlying mathematical formulas for height, diameter, and circumference remain the same.

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