235/55R18 vs 245/55R18
Side-by-side comparison of overall diameter, sidewall height, speedometer error, and ride-height change.
Borderline — Check wheel-arch clearance and reset TPMS before fitting.
To scale
235/55R18
- Section width
- 235 mm
- Aspect ratio
- 55%
- Rim diameter
- 18"
- Sidewall
- 129.3 mm
- Overall diameter
- 715.7 mm
- Circumference
- 2248 mm
- Revs / mile
- 716
- Revs / km
- 445
245/55R18
- Section width
- 245 mm
- Aspect ratio
- 55%
- Rim diameter
- 18"
- Sidewall
- 134.8 mm
- Overall diameter
- 726.7 mm
- Circumference
- 2283 mm
- Revs / mile
- 705
- Revs / km
- 438
Difference
- Overall diameter
- +11.0 mm (+1.54%)
- Sidewall height
- +5.5 mm
- Tread width
- +10 mm
- Ride height (axle)
- +5.5 mm
- Speedometer error
- +1.54%
- At indicated 60 mph
- actual 60.9 mph
- At indicated 100 km/h
- actual 101.5 km/h
Will 245/55R18 fit instead of 235/55R18?
The overall diameter changes by 1.54%. Most manufacturers consider a swap acceptable when the difference stays under 3% — beyond that, you may see speedometer error, ABS/TPMS warnings, or wheel-well clearance problems. This page only covers the math; your vehicle's wheel arches, suspension geometry, and load rating still matter.
What the numbers mean
- Overall diameter — outside-to-outside height of the tire. Affects ride height, gearing, and speedometer calibration.
- Sidewall height — rubber from rim edge to tread. Lower sidewall gives sharper steering response but a harsher ride.
- Speedometer error — how far off your indicated speed will be after the swap. Positive means the speedo under-reads (actual speed is higher than shown).