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
Editorial preset
These are TireFitLab editorial diameter-screening presets. Regional names choose a preset, not a national legal limit, ETRTO rule or vehicle approval. The AWD preset does not establish an allowable drivetrain mismatch. Use the exact vehicle and tyre manufacturer instructions; nominal geometry alone cannot approve fitment.
Editorial preset +max −max Source EU preset (±3%) +3% −3% TireFitLab · Editorial preset PL preset (+1.5/−2%) +1.5% −2% TireFitLab · Editorial preset US preset (±3%) +3% −3% TireFitLab · Editorial preset AWD preset (±2%) +2% −2% TireFitLab · Editorial preset
Last reviewed: 2026-09-04
Note: geometric estimate. Always verify physical clearance before fitting.