215/50R18 vs 265/30R20

265/30R20 is 0.20 in (5.2 mm) shorter than 215/50R18, a −0.77% diameter difference. With the speedometer set for 215/50R18, an indicated 60 mph is 59.5 mph on 265/30R20.

Is this a safe swap?

Diameter difference −0.77%: under 1%

By overall diameter alone, 265/30R20 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 265/30R20 differences
Measurement	215/50R18	265/30R20	Difference	% diff
Overall diameter	26.46 in (672.2 mm)	26.26 in (667.0 mm)	−0.20 in (−5.2 mm)	−0.77%
Sidewall height	4.23 in (107.5 mm)	3.13 in (79.5 mm)	−1.10 in (−28.0 mm)	−26.05%
Section width	8.46 in (215.0 mm)	10.43 in (265.0 mm)	+1.97 in (+50.0 mm)	+23.26%
Circumference	83.14 in (2,111.8 mm)	82.50 in (2,095.4 mm)	−0.64 in (−16.3 mm)	−0.77%
Revolutions per mile	762	768	+6	+0.78%

True speed with the speedometer calibrated for 215/50R18
Indicated	Actual on 215/50R18	Actual on 265/30R20	Difference
30 mph	30.0 mph	29.8 mph	−0.2 mph
60 mph	60.0 mph	59.5 mph	−0.5 mph
75 mph	75.0 mph	74.4 mph	−0.6 mph

Ride-height change: 265/30R20 lowers the vehicle by 0.10 in (2.6 mm) at the axle (half the −5.2 mm diameter difference).

265/30R20 is 0.20 in shorter than 215/50R18 and 50 mm wider, a 0.77% difference in overall diameter.

With the speedometer calibrated for 215/50R18, an indicated 60 mph is actually 59.5 mph on 265/30R20, and revolutions per mile change from 762 to 768.

265/30R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 215/50R18.

Size pages

Other comparisons with 215/50R18

Other comparisons with 265/30R20

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