WheelTireHub tools
Tire Size Calculator
Compare two tire sizes side by side: section width, aspect ratio, sidewall, overall diameter, circumference, revolutions per kilometre and speedometer error.
Current size (A)
That's not a valid tire size. Enter it like 235/55R17 — width, aspect ratio, then rim.
or
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New size (B)
That's not a valid tire size. Enter it like 235/55R17 — width, aspect ratio, then rim.
or
Quick fill
Enter both sizes above to see the comparison.
Diameter comparison (to scale)
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Metric
Size A
Size B
Delta
Section width
mm—
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Aspect ratio
%—
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Sidewall height
mm / in—
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Overall diameter
mm / in—
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Circumference
mm—
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Revolutions
per km—
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How tire sizes work
Stay within ±1.5% diameter delta to keep the speedometer, odometer and ABS calibration accurate. Beyond ±3%, expect fault codes, mileage drift and clearance issues.
Tire-size formatWidth (mm) / aspect (%) R rim (in). Example: 235/55R17 means 235 mm wide, sidewall = 55% of width, mounted on a 17-inch rim.
Speedometer errorIf the new tire is larger, the wheel rotates less per km and the speedometer under-reads. Stay within ±1.5% for daily drivers.
Overall diameterCalculated as (rim × 25.4) + 2 × sidewall, in millimetres. Real rolling radius is 96–98% of this static value due to load deflection.
ClearanceA larger overall diameter eats wheel-well clearance. Always test full steering lock and full suspension compression before driving.
Rim width compatibilityEach tire width has a recommended rim-width range (typically a 2.0″ window). Mounting outside this range distorts the tire profile, hurts handling and may void the warranty. ETRTO chart: 195 mm → 5.5–7″, 215 mm → 6.5–8″, 235 mm → 7.5–9″, 255 mm → 8.5–10″, 275 mm → 9–11″.
Load index & speed ratingWhen changing tire size, the new tire's load index must equal or exceed the OEM rating, and the speed rating must equal or exceed it. Lower-rated tires are unsafe even if dimensions match. The full marking reads e.g. 235/55R17 99V — 99 = load index (775 kg), V = speed rating (240 km/h).
All calculations use the metric tire-size standard (width × aspect / 100 = sidewall mm). Real-world rolling diameter varies by ±1% with load, pressure and tread wear.