TireFitLab

285/60 R18 vs 35x12.50 R20

285/60 R18 vs 35x12.50 R20

35x12.50 R20 is outside the configured tolerance for 285/60 R18: +11.2% diameter and +11.2% speedometer effect.

Fitment verdict

35x12.50 R20 is outside the configured tolerance for 285/60 R18: +11.2% diameter and +11.2% speedometer effect.

Metric This size: 285/60 R18 Alternative: 35x12.50 R20 Difference Verdict
Overall diameter 31.46 in 35.00 in +11.2% Too tall
Section width 11.22 in 12.50 in +1.28 in Computed difference
Sidewall height 6.73 in 7.50 in +0.77 in Computed difference
Circumference 98.85 in 109.96 in +11.2% Too tall
Speedo 0.0% +11.2% +11.2% Outside tolerance

Compare sizes

Looks valid
Looks valid
Units
✕ Out of toleranceDiameter +11.2% (+3.54 in) · US (~3%)
  • Out of tolerance · Diameter +11.2%.
  • Speedo @ 60: 60 mph → 66.7 mph.
  • Sidewall +0.77 in · Width +1.28 in.
Diameter+11.2%+3.54 in
Speedo @ 60+11.2%60 mph → 66.7 mph
Sidewall+0.77 inWidth +1.28 in
How this result is calculated

Computed from nominal tire-size geometry: diameter, circumference and speedometer error. It does not check wheel-arch, suspension or brake clearance.

Methodology
Diameter
31.46 in 35.00 in+3.54 in
Sidewall
6.73 in 7.50 in+0.77 in
Width
11.22 in 12.50 in+1.28 in
Circumference
98.85 in 109.96 in+11.2%
Revs / mile
641 576
Speedo @ 60
60 mph 66.7 mph+11.2%
Δ⌀ +89.8 mm
  • Current — 285/60 R18
  • New — 35x12.50 R20
  • Grounded to the road: the axle rises +1.77 in.

Result report

285/60 R18 35x12.50 R20 · Out of tolerance

Use this size when shopping: 35x12.50 R20

Use this size when shopping

Geometric estimate. Always verify physical clearance (arches, suspension, brakes) before fitting.

Safe alternative sizes

SizeDiameterSpeedo @ 100Use this
−1″ 245/75R17+0.0%+0.0%
OE 285/60R18+0.0%+0.0%
+1″ 265/60R19+0.2%+0.2%
+2″ 265/55R20+0.0%+0.0%

285/60 R18 · 35x12.50 R20 · Methodology

Last reviewed: 2026-06-28
What changed
  • Reviewed deterministic geometry, load/speed references, sitemap inclusion and localized page shell.