Tire size geometry
Tire size geometry: use nominal section width, aspect ratio, rim diameter. Review the formula, worked example and calculation steps.
Inputs
Use the units shown—
Enter your values and select Calculate.
Formula & explanation
Diameter mm = 25.4×rim + 2×width×aspect/100
Variables & units
- Nominal section width
- mm · minimum 1, maximum 1000
- Aspect ratio
- % · minimum 1, maximum 100
- Rim diameter
- in · minimum 1, maximum 100
Worked example
205/55 R16 gives nominal diameter 631.9 mm.
Assumptions
Nominal unloaded geometry. Manufacturer tolerances, load, inflation and tread wear change actual rolling dimensions; not a fitment approval.
Formula version 1.0.0. JavaScript floating-point arithmetic applies. Results display up to 6 decimal places; stored values retain available precision. Use the units shown.
Practice with an example
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