255/65R18 vs 255/70R18
Side-by-side comparison of overall diameter, sidewall height, speedometer error, and ride-height change.
Not recommended — Exceeds the 3% diameter limit — speedometer error and ABS/TPMS issues likely.
To scale
255/65R18
- Section width
- 255 mm
- Aspect ratio
- 65%
- Rim diameter
- 18"
- Sidewall
- 165.8 mm
- Overall diameter
- 788.7 mm
- Circumference
- 2478 mm
- Revs / mile
- 650
- Revs / km
- 404
255/70R18
- Section width
- 255 mm
- Aspect ratio
- 70%
- Rim diameter
- 18"
- Sidewall
- 178.5 mm
- Overall diameter
- 814.2 mm
- Circumference
- 2558 mm
- Revs / mile
- 629
- Revs / km
- 391
Difference
- Overall diameter
- +25.5 mm (+3.23%)
- Sidewall height
- +12.8 mm
- Tread width
- +0 mm
- Ride height (axle)
- +12.8 mm
- Speedometer error
- +3.23%
- At indicated 60 mph
- actual 61.9 mph
- At indicated 100 km/h
- actual 103.2 km/h
Will 255/70R18 fit instead of 255/65R18?
The overall diameter changes by 3.23%. 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).