215/55R18 vs 265/35R20

265/35R20 is 0.01 in (0.2 mm) shorter than 215/55R18, a −0.03% diameter difference. With the speedometer set for 215/55R18, an indicated 60 mph is 60.0 mph on 265/35R20.

Is this a safe swap?

Diameter difference −0.03%: under 1%

By overall diameter alone, 265/35R20 is a near match for 215/55R18; 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.

215/55R18 vs 265/35R20 differences
Measurement	215/55R18	265/35R20	Difference	% diff
Overall diameter	27.31 in (693.7 mm)	27.30 in (693.5 mm)	−0.01 in (−0.2 mm)	−0.03%
Sidewall height	4.66 in (118.3 mm)	3.65 in (92.8 mm)	−1.00 in (−25.5 mm)	−21.56%
Section width	8.46 in (215.0 mm)	10.43 in (265.0 mm)	+1.97 in (+50.0 mm)	+23.26%
Circumference	85.80 in (2,179.3 mm)	85.78 in (2,178.7 mm)	−0.02 in (−0.6 mm)	−0.03%
Revolutions per mile	738	739	0	+0.03%

True speed with the speedometer calibrated for 215/55R18
Indicated	Actual on 215/55R18	Actual on 265/35R20
30 mph	30.0 mph	30.0 mph
60 mph	60.0 mph	60.0 mph
75 mph	75.0 mph	75.0 mph

Ride-height change: 265/35R20 lowers the vehicle by 0.00 in (0.1 mm) at the axle (half the −0.2 mm diameter difference).

265/35R20 is 0.01 in shorter than 215/55R18 and 50 mm wider, a 0.03% difference in overall diameter.

With the speedometer calibrated for 215/55R18, an indicated 60 mph is actually 60.0 mph on 265/35R20, and revolutions per mile change from 738 to 739.

265/35R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 215/55R18.

Size pages

Other comparisons with 215/55R18

Other comparisons with 265/35R20

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