275/70 R18 vs 37x13.50 R20

What changes when you change tire size?

37x13.50 R20 is outside the configured tolerance for 275/70 R18: +11.6% diameter and +11.6% speedometer effect.

Geometric comparison

Geometric comparison
Metric This size: 275/70 R18 Alternative: 37x13.50 R20 Difference Verdict
Overall diameter 33.16 in 37.00 in +11.6% Too tall
Section width 10.83 in 13.50 in +2.67 in Computed difference
Sidewall height 7.58 in 8.50 in +0.92 in Computed difference
Circumference 104.17 in 116.24 in +11.6% Too tall
Speedo 0.0% +11.6% +11.6% Outside tolerance

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Looks valid
Looks valid
Units
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.

Not recommendedOut of tolerance · Diameter +11.6% (+3.84 in) · US preset (±3%)
  • Not recommended · This rating covers tire geometry only, not vehicle compatibility.
  • Diameter +11.6% · Ride-height change +1.92 in.
  • Speedometer reads low · 60 mph → 67.0 mph.
  • Sidewall +0.92 in · Width +2.67 in.
Diameter+11.6%+3.84 in
Speedo @ 60+11.6%60 mph → 67.0 mph
Sidewall+0.92 inWidth +2.67 in
Ride-height change+1.92 inDiameter ÷ 2
How this result is calculated

Computed from nominal tire-size geometry: diameter, circumference and speedometer error. It does not check vehicle placard approval, load/speed rating, rim-width range, wheel-arch, suspension or brake clearance.

Methodology

Before fitting

  • Check the vehicle placard and owner’s manual first.
  • Match or exceed the required load index and speed rating.
  • Confirm rim-width range, bolt pattern, hub bore, offset and fasteners.
  • Inspect wheel-arch, suspension and brake clearance under real vehicle load.
  • Check TPMS, cold pressure and local roadworthiness rules.
Diameter
33.16 in 37.00 in+3.84 in
Sidewall
7.58 in 8.50 in+0.92 in
Width
10.83 in 13.50 in+2.67 in
Circumference
104.17 in 116.24 in+11.6%
Revs / mile
608 545
Speedo @ 60
60 mph 67.0 mph+11.6%
Ride-height change
0.00 in +1.92 in
True distance per 100 indicated
100 mi 111.6 mi+11.6%
Δ⌀ +3.84 inΔ↔ +2.67 in
  • Current — 275/70 R18
  • New — 37x13.50 R20
  • Grounded to the road: the axle rises +1.92 in.

Tires and wheels in one comparison

Result report

275/70 R18 37x13.50 R20 · Not recommended · Out of tolerance

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

In-tolerance alternative sizes

In-tolerance alternative sizes
SizeDiameterSpeedo @ 100Use this
−1″ 285/70R17-1.4%-1.4%
OE 275/70R18+0.0%+0.0%
+1″ 285/65R19+1.3%+1.3%
+2″ 275/65R20+2.8%+2.8%

275/70 R18 · 37x13.50 R20 · Methodology