245/60R18 vs 255/60R18

255/60R18 is 0.47 in (12.0 mm) taller than 245/60R18, a +1.60% diameter difference. With the speedometer set for 245/60R18, an indicated 60 mph is 61.0 mph on 255/60R18.

Is this a safe swap?

Diameter difference +1.60%: within the ±3% guideline

By overall diameter alone, 255/60R18 falls inside the ±3% range commonly used as a guideline when replacing 245/60R18. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

Side profile and tread width, drawn to the same scale.

245/60R18 vs 255/60R18 differences
Measurement	245/60R18	255/60R18	Difference	% diff
Overall diameter	29.57 in (751.2 mm)	30.05 in (763.2 mm)	+0.47 in (+12.0 mm)	+1.60%
Sidewall height	5.79 in (147.0 mm)	6.02 in (153.0 mm)	+0.24 in (+6.0 mm)	+4.08%
Section width	9.65 in (245.0 mm)	10.04 in (255.0 mm)	+0.39 in (+10.0 mm)	+4.08%
Circumference	92.91 in (2,360.0 mm)	94.40 in (2,397.7 mm)	+1.48 in (+37.7 mm)	+1.60%
Revolutions per mile	682	671	−11	−1.57%

True speed with the speedometer calibrated for 245/60R18
Indicated	Actual on 245/60R18	Actual on 255/60R18	Difference
30 mph	30.0 mph	30.5 mph	+0.5 mph
60 mph	60.0 mph	61.0 mph	+1.0 mph
75 mph	75.0 mph	76.2 mph	+1.2 mph

Ride-height change: 255/60R18 raises the vehicle by 0.24 in (6.0 mm) at the axle (half the +12.0 mm diameter difference).

255/60R18 is 0.47 in taller than 245/60R18 and 10 mm wider, a 1.60% difference in overall diameter.

With the speedometer calibrated for 245/60R18, an indicated 60 mph is actually 61.0 mph on 255/60R18, and revolutions per mile change from 682 to 671.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 245/60R18

Other comparisons with 255/60R18

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.