245/35R18 vs 255/35R18

255/35R18 is 0.28 in (7.0 mm) taller than 245/35R18, a +1.11% diameter difference. With the speedometer set for 245/35R18, an indicated 60 mph is 60.7 mph on 255/35R18.

Is this a safe swap?

Diameter difference +1.11%: within the ±3% guideline

By overall diameter alone, 255/35R18 falls inside the ±3% range commonly used as a guideline when replacing 245/35R18. 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.

245/35R18 vs 255/35R18 differences
Measurement	245/35R18	255/35R18	Difference	% diff
Overall diameter	24.75 in (628.7 mm)	25.03 in (635.7 mm)	+0.28 in (+7.0 mm)	+1.11%
Sidewall height	3.38 in (85.8 mm)	3.51 in (89.3 mm)	+0.14 in (+3.5 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	77.76 in (1,975.1 mm)	78.63 in (1,997.1 mm)	+0.87 in (+22.0 mm)	+1.11%
Revolutions per mile	815	806	−9	−1.10%

True speed with the speedometer calibrated for 245/35R18
Indicated	Actual on 245/35R18	Actual on 255/35R18	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.8 mph	+0.8 mph

Ride-height change: 255/35R18 raises the vehicle by 0.14 in (3.5 mm) at the axle (half the +7.0 mm diameter difference).

255/35R18 is 0.28 in taller than 245/35R18 and 10 mm wider, a 1.11% difference in overall diameter.

With the speedometer calibrated for 245/35R18, an indicated 60 mph is actually 60.7 mph on 255/35R18, and revolutions per mile change from 815 to 806.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 245/35R18

Other comparisons with 255/35R18

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