265/60R18 vs 235/55R20

235/55R20 is 0.34 in (8.7 mm) shorter than 265/60R18, a −1.12% diameter difference. With the speedometer set for 265/60R18, an indicated 60 mph is 59.3 mph on 235/55R20.

Is this a safe swap?

Diameter difference −1.12%: within the ±3% guideline

By overall diameter alone, 235/55R20 falls inside the ±3% range commonly used as a guideline when replacing 265/60R18. 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.

265/60R18 vs 235/55R20 differences
Measurement	265/60R18	235/55R20	Difference	% diff
Overall diameter	30.52 in (775.2 mm)	30.18 in (766.5 mm)	−0.34 in (−8.7 mm)	−1.12%
Sidewall height	6.26 in (159.0 mm)	5.09 in (129.3 mm)	−1.17 in (−29.7 mm)	−18.71%
Section width	10.43 in (265.0 mm)	9.25 in (235.0 mm)	−1.18 in (−30.0 mm)	−11.32%
Circumference	95.88 in (2,435.4 mm)	94.80 in (2,408.0 mm)	−1.08 in (−27.3 mm)	−1.12%
Revolutions per mile	661	668	+8	+1.14%

True speed with the speedometer calibrated for 265/60R18
Indicated	Actual on 265/60R18	Actual on 235/55R20	Difference
30 mph	30.0 mph	29.7 mph	−0.3 mph
60 mph	60.0 mph	59.3 mph	−0.7 mph
75 mph	75.0 mph	74.2 mph	−0.8 mph

Ride-height change: 235/55R20 lowers the vehicle by 0.17 in (4.4 mm) at the axle (half the −8.7 mm diameter difference).

235/55R20 is 0.34 in shorter than 265/60R18 and 30 mm narrower, a 1.12% difference in overall diameter.

With the speedometer calibrated for 265/60R18, an indicated 60 mph is actually 59.3 mph on 235/55R20, and revolutions per mile change from 661 to 668.

235/55R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 265/60R18.

Size pages

Other comparisons with 265/60R18

Other comparisons with 235/55R20

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