TireFitLab

285/50 R20

What size is 285/50 R20?

285/50 R20 has an overall diameter of about 31.22 in, a section width of 11.22 in and a sidewall height of 5.61 in. It turns roughly 646 times per mile. Below are the exact figures plus plus/minus sizes that stay within the selected diameter tolerance.

Geometric comparison

31x10.50 R15 stays within the configured tolerance for 285/50 R20: -0.7% diameter and -0.7% speedometer effect.

Geometric comparison
Metric This size: 285/50 R20 Alternative: 31x10.50 R15 Difference Verdict
Overall diameter 31.22 in 31.00 in -0.7% Within tolerance
Section width 11.22 in 10.50 in -0.72 in Computed difference
Sidewall height 5.61 in 8.00 in +2.39 in Computed difference
Circumference 98.08 in 97.39 in -0.7% Within tolerance
Speedo 0.0% -0.7% -0.7% Within tolerance

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What this geometry means

285/50 R20 has a mid-range sidewall proportion. The marking combines nominal section width 11.22 in, sidewall ratio 50% and rim diameter 20 inches. One sidewall is 5.61 in; both sidewalls make up 36% of the 31.22 in overall diameter, while the rim makes up 64%.

At the nominal 98.08 in circumference, 1,000 rotations cover 2.49 km (1.55 mi); the inverse rates are 401/km and 646/mi.

Section-width mix versus 285/50 R20: 9 narrower, 2 equal-width and 1 wider entries.

The closest diameter entry is 31x10.50 R15 at -0.7%. Relative to 285/50 R20, it changes nominal section width by -0.72 in, each sidewall by +2.39 in and radius by -0.11 in.

Curated alternatives: 12 sizes, spanning -2.1% to +1.7% in nominal diameter versus 285/50 R20.

Width endpoints in that set are 265/65 R18 (-0.79 in) and 305/40 R22 (+0.79 in) relative to 285/50 R20.

This is a nominal geometry comparison only. Vehicle clearance, wheel width and offset, load and speed ratings, and manufacturer approval still require separate checks.

Specification

Specification
Overall diameter 31.22 in
Section width 11.22 in
Sidewall height 5.61 in
Circumference 98.08 in
Revolutions 401 /km · 646 /mi

In-tolerance sizes

Alternative sizes that stay within the selected diameter tolerance:

In-tolerance sizes
Size Diameter Speedo Verdict
31x10.50 R15 -0.7% -0.7% ✓ OK
31x10.50 R16 -0.7% -0.7% ✓ OK
285/60 R18 +0.8% +0.8% ✓ OK
285/40 R22 -0.8% -0.8% ✓ OK
275/55 R19 -1.0% -1.0% ✓ OK
265/65 R18 +1.1% +1.1% ✓ OK
265/70 R17 +1.2% +1.2% ✓ OK
305/40 R22 +1.2% +1.2% ✓ OK
275/45 R21 -1.5% -1.5% ✓ OK
275/45 R22 +1.7% +1.7% ✓ OK
265/70 R16 -2.0% -2.0% ✓ OK
265/65 R17 -2.1% -2.1% ✓ OK

Compare sizes

Looks valid
Looks valid
Units
Not recommendedWithin tolerance · Diameter -0.7% (-0.22 in) · US (~3%)
  • Not recommended · This rating covers tire geometry only, not vehicle compatibility.
  • Diameter -0.7% · Ride-height change -0.11 in.
  • Speedometer reads high · 60 mph → 59.6 mph.
  • Sidewall +2.39 in · Width -0.72 in.
Diameter-0.7%-0.22 in
Speedo @ 60-0.7%60 mph → 59.6 mph
Sidewall+2.39 inWidth -0.72 in
Ride-height change-0.11 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
31.22 in 31.00 in-0.22 in
Sidewall
5.61 in 8.00 in+2.39 in
Width
11.22 in 10.50 in-0.72 in
Circumference
98.08 in 97.39 in-0.7%
Revs / mile
646 651
Speedo @ 60
60 mph 59.6 mph-0.7%
Ride-height change
0.00 in -0.11 in
True distance per 100 indicated
100 mi 99.3 mi-0.7%
Δ⌀ -0.22 inΔ↔ -0.72 in
  • Current — 285/50 R20
  • New — 31x10.50 R15
  • Grounded to the road: the axle rises -0.11 in.

Result report

285/50 R20 31x10.50 R15 · Not recommended · Within 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
OE 285/50R20+0.0%+0.0%

More tools

Last reviewed: 2026-07-22

Technical check
2026-07-22
Content updated
2026-07-22
What changed
  • Added a localized engine-derived geometry signature and matching Markdown narrative.
Methodology