Tire Size Calculator
Compare two tire sizes and see how their dimensions differ. Calculate sidewall height, overall diameter, circumference, ground clearance change and speedometer difference.
Enter tire sizes using the standard format such as 225/45R17, or enter the dimensions manually.
Compare Tire Sizes
Enter the original and new tire dimensions to compare their measurements.
Original Tire
New Tire
Speedometer Comparison
Tire Size Comparison Results
Tire Size Summary
Original Diameter
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New Diameter
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Diameter Difference
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Diameter Change
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What Does a Tire Size Mean?
A tire size such as 225/45R17 contains several important measurements. The first number, 225, represents the tire width in millimeters. The second number, 45, is the aspect ratio, meaning the sidewall height is 45% of the tire width.
The letter R indicates radial construction, while 17 represents the wheel rim diameter in inches.
| Part | Example | Meaning |
|---|---|---|
| Width | 225 | 225 mm tire width |
| Aspect Ratio | 45 | Sidewall is 45% of width |
| Construction | R | Radial construction |
| Rim Diameter | 17 | 17-inch wheel |
How Tire Size Is Calculated
The calculator uses the tire width, aspect ratio and rim diameter to estimate the overall tire diameter and circumference.
Sidewall Height
Sidewall height = Tire width ร Aspect ratio รท 100
Overall Diameter
Overall diameter = (2 ร Sidewall height) + Rim diameter
Because tire width is measured in millimeters and rim diameter is measured in inches, the calculator converts the measurements to the same unit before calculating the final diameter.
Circumference
Circumference = ฯ ร Overall diameter
Tire Size Comparison Example
Suppose a vehicle currently uses 225/45R17 tires and you want to compare them with 235/45R17.
The new tire is wider, while the width and rim diameter changes determine whether its overall diameter becomes larger or smaller.
Comparing the overall diameter is important because a significant change can affect speedometer readings, ground clearance, gearing and available space around the tire.
Why Tire Size Comparison Matters
Changing tire size is more than simply choosing a wider or larger tire. The overall diameter can change even when the wheel diameter stays the same.
A larger overall diameter can increase ground clearance and change the distance traveled per wheel revolution. A smaller diameter can have the opposite effect.
Tire-size changes can also affect speedometer accuracy, handling, acceleration, braking characteristics and clearance. Always check your vehicle manufacturer's approved tire sizes before purchasing replacement tires.
Frequently Asked Questions
What is a tire size calculator?
A tire size calculator compares tire dimensions and estimates measurements such as sidewall height, overall diameter, circumference and percentage difference.
Does changing tire size affect the speedometer?
Yes. If the overall tire diameter changes, the distance traveled per wheel revolution also changes. This can cause the actual vehicle speed to differ from the speedometer reading.
Does a wider tire always have a larger diameter?
No. Tire width and overall diameter are separate measurements. The aspect ratio and rim diameter also determine the final overall diameter.
Can I use this calculator for cars and motorcycles?
Yes. The mathematical comparison can be used for many vehicles that use conventional tire-size measurements. However, always confirm manufacturer-approved sizes and physical clearance before fitting a different tire.
What percentage difference is acceptable?
There is no universal percentage that is appropriate for every vehicle. Vehicle manufacturers specify compatible tire sizes, and factors such as clearance, load rating, wheel width and drivetrain requirements also matter.