Tire Size Comparison
Compare two tire sizes for diameter and speedometer difference.
About Tire Size Comparison
Tire diameter combines the rim plus twice the sidewall height, which depends on width and aspect ratio. The percentage difference tells you how far the two sizes drift apart. Changing tire diameter by more than a few percent skews the speedometer and odometer and can affect gearing and ground clearance.
Formula
Tire Size Comparison
Diameter = rim x 25.4 + 2 x (width x aspect%)
- aspect ratio
- Sidewall height as a percentage of tire width
Worked example
With the default values below, Tire Size Comparison returns Diameter 1 of 634.3. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Tire 1 widthminimum 20 mm
- 225 mm
- Tire 1 aspect ratioaccepts 10–90 %
- 45 %
- Tire 1 rimminimum 1 in
- 17 in
- Tire 2 widthminimum 20 mm
- 235 mm
- Tire 2 aspect ratioaccepts 10–90 %
- 40 %
- Tire 2 rimminimum 1 in
- 18 in
Results
- Diameter 1
- 634.3 mm
- Diameter 2
- 645.2 mm
- Diameter Difference
- 1.72%
Step by step
- 1Values used
- 2Tire Size Comparison
- 3Diameter 1= 634.3 mm
- 4Diameter 2= 645.2 mm
- 5Diameter Difference= 1.72
Assumptions and limits
- The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Tire Size Comparison calculated?
Diameter = rim x 25.4 + 2 x (width x aspect%) Tire diameter combines the rim plus twice the sidewall height, which depends on width and aspect ratio. The percentage difference tells you how far the two sizes drift apart.
Why does Tire Size Comparison matter?
Changing tire diameter by more than a few percent skews the speedometer and odometer and can affect gearing and ground clearance.
What values do I need to enter?
This calculator takes 6 inputs: Tire 1 width, Tire 1 aspect ratio, Tire 1 rim, Tire 2 width, Tire 2 aspect ratio, Tire 2 rim. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.