225/45R18 vs 245/45R18

245/45R18 is 0.71 in (18.0 mm) taller than 225/45R18, a +2.73% diameter difference. With the speedometer set for 225/45R18, an indicated 60 mph is 61.6 mph on 245/45R18.

Is this a safe swap?

Diameter difference +2.73%: within the ±3% guideline

By overall diameter alone, 245/45R18 falls inside the ±3% range commonly used as a guideline when replacing 225/45R18. 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.

225/45R18 vs 245/45R18 differences
Measurement	225/45R18	245/45R18	Difference	% diff
Overall diameter	25.97 in (659.7 mm)	26.68 in (677.7 mm)	+0.71 in (+18.0 mm)	+2.73%
Sidewall height	3.99 in (101.3 mm)	4.34 in (110.3 mm)	+0.35 in (+9.0 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	81.59 in (2,072.5 mm)	83.82 in (2,129.1 mm)	+2.23 in (+56.5 mm)	+2.73%
Revolutions per mile	777	756	−21	−2.66%

True speed with the speedometer calibrated for 225/45R18
Indicated	Actual on 225/45R18	Actual on 245/45R18	Difference
30 mph	30.0 mph	30.8 mph	+0.8 mph
60 mph	60.0 mph	61.6 mph	+1.6 mph
75 mph	75.0 mph	77.0 mph	+2.0 mph

Ride-height change: 245/45R18 raises the vehicle by 0.35 in (9.0 mm) at the axle (half the +18.0 mm diameter difference).

245/45R18 is 0.71 in taller than 225/45R18 and 20 mm wider, a 2.73% difference in overall diameter.

With the speedometer calibrated for 225/45R18, an indicated 60 mph is actually 61.6 mph on 245/45R18, and revolutions per mile change from 777 to 756.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 225/45R18

Other comparisons with 245/45R18

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