215/50R18 vs 245/45R18

245/45R18 is 0.22 in (5.5 mm) taller than 215/50R18, a +0.82% diameter difference. With the speedometer set for 215/50R18, an indicated 60 mph is 60.5 mph on 245/45R18.

Is this a safe swap?

Diameter difference +0.82%: under 1%

By overall diameter alone, 245/45R18 is a near match for 215/50R18; the speedometer changes by less than 1%. 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.

215/50R18 vs 245/45R18 differences
Measurement	215/50R18	245/45R18	Difference	% diff
Overall diameter	26.46 in (672.2 mm)	26.68 in (677.7 mm)	+0.22 in (+5.5 mm)	+0.82%
Sidewall height	4.23 in (107.5 mm)	4.34 in (110.3 mm)	+0.11 in (+2.8 mm)	+2.56%
Section width	8.46 in (215.0 mm)	9.65 in (245.0 mm)	+1.18 in (+30.0 mm)	+13.95%
Circumference	83.14 in (2,111.8 mm)	83.82 in (2,129.1 mm)	+0.68 in (+17.3 mm)	+0.82%
Revolutions per mile	762	756	−6	−0.81%

True speed with the speedometer calibrated for 215/50R18
Indicated	Actual on 215/50R18	Actual on 245/45R18	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.5 mph	+0.5 mph
75 mph	75.0 mph	75.6 mph	+0.6 mph

Ride-height change: 245/45R18 raises the vehicle by 0.11 in (2.8 mm) at the axle (half the +5.5 mm diameter difference).

245/45R18 is 0.22 in taller than 215/50R18 and 30 mm wider, a 0.82% difference in overall diameter.

With the speedometer calibrated for 215/50R18, an indicated 60 mph is actually 60.5 mph on 245/45R18, and revolutions per mile change from 762 to 756.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 215/50R18

Other comparisons with 245/45R18

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