245/65R18 vs 255/65R18

255/65R18 is 0.51 in (13.0 mm) taller than 245/65R18, a +1.68% diameter difference. With the speedometer set for 245/65R18, an indicated 60 mph is 61.0 mph on 255/65R18.

Is this a safe swap?

Diameter difference +1.68%: within the ±3% guideline

By overall diameter alone, 255/65R18 falls inside the ±3% range commonly used as a guideline when replacing 245/65R18. 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.

245/65R18 vs 255/65R18 differences
Measurement	245/65R18	255/65R18	Difference	% diff
Overall diameter	30.54 in (775.7 mm)	31.05 in (788.7 mm)	+0.51 in (+13.0 mm)	+1.68%
Sidewall height	6.27 in (159.3 mm)	6.53 in (165.8 mm)	+0.26 in (+6.5 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	95.94 in (2,436.9 mm)	97.55 in (2,477.8 mm)	+1.61 in (+40.8 mm)	+1.68%
Revolutions per mile	660	650	−11	−1.65%

True speed with the speedometer calibrated for 245/65R18
Indicated	Actual on 245/65R18	Actual on 255/65R18	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	76.3 mph	+1.3 mph

Ride-height change: 255/65R18 raises the vehicle by 0.26 in (6.5 mm) at the axle (half the +13.0 mm diameter difference).

255/65R18 is 0.51 in taller than 245/65R18 and 10 mm wider, a 1.68% difference in overall diameter.

With the speedometer calibrated for 245/65R18, an indicated 60 mph is actually 61.0 mph on 255/65R18, and revolutions per mile change from 660 to 650.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 245/65R18

Other comparisons with 255/65R18

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