TireFitLab

31x10.50 R15 vs 285/65 R18

31x10.50 R15 vs 285/65 R18

285/65 R18 is outside the configured tolerance for 31x10.50 R15: +5.1% diameter and +5.1% speedometer effect.

Fitment verdict

285/65 R18 is outside the configured tolerance for 31x10.50 R15: +5.1% diameter and +5.1% speedometer effect.

Metric This size: 31x10.50 R15 Alternative: 285/65 R18 Difference Verdict
Overall diameter 31.00 in 32.59 in +5.1% Too tall
Section width 10.50 in 11.22 in +0.72 in Computed difference
Sidewall height 8.00 in 7.29 in -0.71 in Computed difference
Circumference 97.39 in 102.37 in +5.1% Too tall
Speedo 0.0% +5.1% +5.1% Outside tolerance

Compare sizes

Looks valid
Looks valid
Units
✕ Out of toleranceDiameter +5.1% (+1.59 in) · US (~3%)
  • Out of tolerance · Diameter +5.1%.
  • Speedo @ 60: 60 mph → 63.1 mph.
  • Sidewall -0.71 in · Width +0.72 in.
Diameter+5.1%+1.59 in
Speedo @ 60+5.1%60 mph → 63.1 mph
Sidewall-0.71 inWidth +0.72 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
31.00 in 32.59 in+1.59 in
Sidewall
8.00 in 7.29 in-0.71 in
Width
10.50 in 11.22 in+0.72 in
Circumference
97.39 in 102.37 in+5.1%
Revs / mile
651 619
Speedo @ 60
60 mph 63.1 mph+5.1%
Δ⌀ +40.3 mm
  • Current — 31x10.50 R15
  • New — 285/65 R18
  • Grounded to the road: the axle rises +0.79 in.

Result report

31x10.50 R15 285/65 R18 · Out of tolerance

Use this size when shopping: 285/65 R18

Use this size when shopping

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

Safe alternative sizes

SizeDiameterSpeedo @ 100Use this
−1″ 335/65R14+0.5%+0.5%
OE 255/80R15+0.2%+0.2%
+1″ 345/55R16-0.2%-0.2%
+2″ 355/50R17-0.1%-0.1%

31x10.50 R15 · 285/65 R18 · Methodology

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