235/50R18 vs 265/35R20

265/35R20 is 0.05 in (1.3 mm) taller than 235/50R18, a +0.19% diameter difference. With the speedometer set for 235/50R18, an indicated 60 mph is 60.1 mph on 265/35R20.

Is this a safe swap?

Diameter difference +0.19%: under 1%

By overall diameter alone, 265/35R20 is a near match for 235/50R18; 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.

235/50R18 vs 265/35R20 differences
Measurement	235/50R18	265/35R20	Difference	% diff
Overall diameter	27.25 in (692.2 mm)	27.30 in (693.5 mm)	+0.05 in (+1.3 mm)	+0.19%
Sidewall height	4.63 in (117.5 mm)	3.65 in (92.8 mm)	−0.97 in (−24.7 mm)	−21.06%
Section width	9.25 in (235.0 mm)	10.43 in (265.0 mm)	+1.18 in (+30.0 mm)	+12.77%
Circumference	85.61 in (2,174.6 mm)	85.78 in (2,178.7 mm)	+0.16 in (+4.1 mm)	+0.19%
Revolutions per mile	740	739	−1	−0.19%

True speed with the speedometer calibrated for 235/50R18
Indicated	Actual on 235/50R18	Actual on 265/35R20	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.1 mph	+0.1 mph
75 mph	75.0 mph	75.1 mph	+0.1 mph

Ride-height change: 265/35R20 raises the vehicle by 0.03 in (0.6 mm) at the axle (half the +1.3 mm diameter difference).

265/35R20 is 0.05 in taller than 235/50R18 and 30 mm wider, a 0.19% difference in overall diameter.

With the speedometer calibrated for 235/50R18, an indicated 60 mph is actually 60.1 mph on 265/35R20, and revolutions per mile change from 740 to 739.

265/35R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 235/50R18.

Size pages

Other comparisons with 235/50R18

Other comparisons with 265/35R20

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