255/40 R19 vs 235/50 R18

What changes when you change tire size?

235/50 R18 stays within the configured tolerance for 255/40 R19: +0.8% diameter and +0.8% speedometer effect.

Geometric comparison

Geometric comparison
Metric This size: 255/40 R19 Alternative: 235/50 R18 Difference Verdict
Overall diameter 27.03 in 27.25 in +0.8% Within tolerance
Section width 10.04 in 9.25 in -0.79 in Computed difference
Sidewall height 4.02 in 4.63 in +0.61 in Computed difference
Circumference 84.92 in 85.61 in +0.8% Within tolerance
Speedo 0.0% +0.8% +0.8% Within tolerance

Compare sizes

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.

Requires verificationWithin tolerance · Diameter +0.8% (+0.22 in) · US preset (±3%)
  • Requires verification · This rating covers tire geometry only, not vehicle compatibility.
  • Diameter +0.8% · Ride-height change +0.11 in.
  • Speedometer reads low · 60 mph → 60.5 mph.
  • Sidewall +0.61 in · Width -0.79 in.
Diameter+0.8%+0.22 in
Speedo @ 60+0.8%60 mph → 60.5 mph
Sidewall+0.61 inWidth -0.79 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
27.03 in 27.25 in+0.22 in
Sidewall
4.02 in 4.63 in+0.61 in
Width
10.04 in 9.25 in-0.79 in
Circumference
84.92 in 85.61 in+0.8%
Revs / mile
746 740
Speedo @ 60
60 mph 60.5 mph+0.8%
Ride-height change
0.00 in +0.11 in
True distance per 100 indicated
100 mi 100.8 mi+0.8%
Δ⌀ +0.22 inΔ↔ -0.79 in
  • Current — 255/40 R19
  • New — 235/50 R18
  • Grounded to the road: the axle rises +0.11 in.

Tires and wheels in one comparison

Result report

255/40 R19 235/50 R18 · Requires verification · Within tolerance

Plan budget for this size: 235/50 R18

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Plan budget for this size
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Estimated budgetBudget$85–$120Per tireMid-range$110–$160Per tirePremium$160–$225Per tire

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

In-tolerance alternative sizes

In-tolerance alternative sizes
SizeDiameterSpeedo @ 100Use this
−1″ 245/45R18-1.3%-1.3%
OE 255/40R19+0.0%+0.0%
+1″ 265/35R20+1.0%+1.0%
+2″ 265/30R21+0.8%+0.8%

255/40 R19 · 235/50 R18 · Methodology