225/35R18 vs 245/35R18

245/35R18 is 0.55 in (14.0 mm) taller than 225/35R18, a +2.28% diameter difference. With the speedometer set for 225/35R18, an indicated 60 mph is 61.4 mph on 245/35R18.

Is this a safe swap?

Diameter difference +2.28%: within the ±3% guideline

By overall diameter alone, 245/35R18 falls inside the ±3% range commonly used as a guideline when replacing 225/35R18. 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.

225/35R18 vs 245/35R18 differences
Measurement	225/35R18	245/35R18	Difference	% diff
Overall diameter	24.20 in (614.7 mm)	24.75 in (628.7 mm)	+0.55 in (+14.0 mm)	+2.28%
Sidewall height	3.10 in (78.8 mm)	3.38 in (85.8 mm)	+0.28 in (+7.0 mm)	+8.89%
Section width	8.86 in (225.0 mm)	9.65 in (245.0 mm)	+0.79 in (+20.0 mm)	+8.89%
Circumference	76.03 in (1,931.1 mm)	77.76 in (1,975.1 mm)	+1.73 in (+44.0 mm)	+2.28%
Revolutions per mile	833	815	−19	−2.23%

True speed with the speedometer calibrated for 225/35R18
Indicated	Actual on 225/35R18	Actual on 245/35R18	Difference
30 mph	30.0 mph	30.7 mph	+0.7 mph
60 mph	60.0 mph	61.4 mph	+1.4 mph
75 mph	75.0 mph	76.7 mph	+1.7 mph

Ride-height change: 245/35R18 raises the vehicle by 0.28 in (7.0 mm) at the axle (half the +14.0 mm diameter difference).

245/35R18 is 0.55 in taller than 225/35R18 and 20 mm wider, a 2.28% difference in overall diameter.

With the speedometer calibrated for 225/35R18, an indicated 60 mph is actually 61.4 mph on 245/35R18, and revolutions per mile change from 833 to 815.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 225/35R18

Other comparisons with 245/35R18

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