275/65 R18 vs 37x13.50 R20

What changes when you change tire size?

37x13.50 R20 is outside the configured tolerance for 275/65 R18: +15.4% diameter and +15.4% speedometer effect.

Geometric comparison

Geometric comparison
Metric This size: 275/65 R18 Alternative: 37x13.50 R20 Difference Verdict
Overall diameter 32.07 in 37.00 in +15.4% Too tall
Section width 10.83 in 13.50 in +2.67 in Computed difference
Sidewall height 7.04 in 8.50 in +1.46 in Computed difference
Circumference 100.77 in 116.24 in +15.4% Too tall
Speedo 0.0% +15.4% +15.4% 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 +15.4% (+4.93 in) · US preset (±3%)
  • Not recommended · This rating covers tire geometry only, not vehicle compatibility.
  • Diameter +15.4% · Ride-height change +2.46 in.
  • Speedometer reads low · 60 mph → 69.2 mph.
  • Sidewall +1.46 in · Width +2.67 in.
Diameter+15.4%+4.93 in
Speedo @ 60+15.4%60 mph → 69.2 mph
Sidewall+1.46 inWidth +2.67 in
Ride-height change+2.46 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
32.07 in 37.00 in+4.93 in
Sidewall
7.04 in 8.50 in+1.46 in
Width
10.83 in 13.50 in+2.67 in
Circumference
100.77 in 116.24 in+15.4%
Revs / mile
629 545
Speedo @ 60
60 mph 69.2 mph+15.4%
Ride-height change
0.00 in +2.46 in
True distance per 100 indicated
100 mi 115.4 mi+15.4%
Δ⌀ +4.93 inΔ↔ +2.67 in
  • Current — 275/65 R18
  • New — 37x13.50 R20
  • Grounded to the road: the axle rises +2.46 in.

Tires and wheels in one comparison

Result report

275/65 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″ 265/70R17-1.5%-1.5%
OE 275/65R18+0.0%+0.0%
+1″ 285/60R19+1.2%+1.2%
+2″ 275/60R20+2.9%+2.9%

275/65 R18 · 37x13.50 R20 · Methodology