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Rolling circumference & speedometer error

The rolling circumference defines how far the car travels per wheel revolution. If it changes, speedometer and odometer read wrong – which makes it the key value for every wheel upgrade.

Rolling circumference = π × DDRolling circumference = π × D1 revolution →
One wheel revolution equals the rolling circumference

Static vs. dynamic

The static circumference is pure geometry: π × overall diameter. Under load the tyre deflects, so the dynamic rolling circumference is about 2–3 % smaller. Tyre makers list it in data sheets; the calculator uses an approximation factor.

Circumference (static) = π × D
Rolling circumference ≈ circumference × 0.975
Deviation % = (C_new / C_stock − 1) × 100

Tolerance for approval

As a guideline, German testing organisations accept a rolling circumference deviation of −2 % to +1.5 % compared with the stock size. Larger deviations usually require speedometer recalibration or an individual approval.

These values drive the calculator. Legal limits are binding, guidelines and orientation values help you assess.

Rolling circumference vs. stock-2 % to +1.5 %GuidelineVdTÜV-Merkblatt 751
Speedometer lead0 to 10 % + 4 km/h, never below real speedLegalUN-R39 / § 57 StVZO
Rim width for the tyreApproved range per ETRTO tableGuidelineETRTO Standards Manual
Load indexat least the value in the papersLegal§ 36 StVZO / COC
Speed ratingat least the papers' value (winter tyres: sticker)Legal§ 36 StVZO / COC
Wheel cover30° ahead to 50° behind the wheel centreLegalVO (EU) 1009/2010
Track wideningcheck closely above ±2 %OrientationOrientierungswert
Remaining fender gap≥ 5 mmOrientationOrientierungswert
Remaining strut gap≥ 5 mmOrientationOrientierungswert
Thread engagement≥ 1 × thread diameterGuidelineFaustregel (≥ 1 × d)

What happens to the speedometer?

  • Larger circumference → the wheel turns less often → the speedo shows less than you drive. Critical, because that is not allowed.
  • Smaller circumference → the speedo shows more. Allowed as long as the lead stays within limits.

Other effects

  • Odometer and fuel consumption display deviate by the same ratio.
  • Effective gearing becomes longer (larger circumference) or shorter.
  • ABS/ESP compare wheel speeds – different circumferences per axle only with approval.

Try it: enter your values in the calculator and see what changes live.

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General information without warranty – no legal advice. Vehicle documents, certificates and the inspector are authoritative.

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