How TireFitLab calculates fitment
Every figure is computed from the tire size in canonical millimetres — the same engine powers the calculator, the size pages and the comparisons, so the numbers are identical everywhere.
Formulas
| Sidewall height | width × aspect ÷ 100 |
|---|---|
| Overall diameter | rim + 2 × sidewall |
| Circumference | π × diameter |
| Speedometer error | (newØ − oldØ) ÷ oldØ × 100% |
Geometry screening
This rating covers tire geometry only, not vehicle compatibility. The highest triggered level applies.
Geometry screening How this result is calculated Very close match |Δ Diameter| ≤ 0.5% · |Δ Width| ≤ 10 mm · |Δ Sidewall| ≤ 5 mm Minor variation |Δ Diameter| ≤ 1.5% · |Δ Width| ≤ 20 mm · |Δ Sidewall| ≤ 12.5 mm Requires verification |Δ Diameter| > 1.5% / |Δ Width| > 20 mm / |Δ Sidewall| > 12.5 mm High fitment risk Out of tolerance / |Δ Width| ≥ 40 mm / |Δ Sidewall| ≥ 25 mm Not recommended |Δ Diameter| ≥ 6% / |Δ Width| ≥ 60 mm / |Δ Sidewall| ≥ 40 mm
Tolerance rules
The following tolerances are a working baseline and must be verified per market against a primary source.
Market +max −max Source EU general (±3%) +3% −3% ETRTO / common EU practice Poland +1.5% −2% PL national guidance US (~3%) +3% −3% Tire industry common practice / T&RA AWD / 4WD (tight) +2% −2% Drivetrain rolling-radius guidance
Last reviewed: 2026-07-16
Note: geometric estimate. Always verify physical clearance before fitting.
- Content updated
- 2026-07-16
What changed
- Checked generated routes, metadata, sitemap inclusion and localized page rendering.