215/60R16 vs 255/40R18
Comparison of overall diameter, sidewall, speedometer error, and ride-height change between these two tire sizes.
215/60R16
- Section width
- 215 mm
- Aspect ratio
- 60%
- Rim
- 16"
- Sidewall
- 129.0 mm
- Overall diameter
- 664.4 mm
- Revs / mile
- 771
255/40R18
- Section width
- 255 mm
- Aspect ratio
- 40%
- Rim
- 18"
- Sidewall
- 102.0 mm
- Overall diameter
- 661.2 mm
- Revs / mile
- 775
Difference
- Overall diameter
- -3.2 mm (-0.48%)
- Sidewall
- -27.0 mm
- Tread width
- +40 mm
- Ride height (axle)
- -1.6 mm
- Speedometer error
- -0.48%
- At indicated 60 mph
- actual 59.71 mph
Will 255/40R18 fit instead of 215/60R16?
The overall diameter changes by 0.48%. 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 is the outside-to-outside height of the tire. Affects ride height, gearing, and speedometer.
- Sidewall is the height of the rubber from rim to tread. Lower sidewall = sharper steering, harsher ride.
- Speedometer error is the percentage your indicated speed will be off after the swap (positive = speedo reads lower than actual).