255/70R18 vs 265/60R20

265/60R20 is 0.46 in (11.8 mm) taller than 255/70R18, a +1.45% diameter difference. With the speedometer set for 255/70R18, an indicated 60 mph is 60.9 mph on 265/60R20.

Is this a safe swap?

Diameter difference +1.45%: within the ±3% guideline

By overall diameter alone, 265/60R20 falls inside the ±3% range commonly used as a guideline when replacing 255/70R18. 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.

255/70R18 vs 265/60R20 differences
Measurement	255/70R18	265/60R20	Difference	% diff
Overall diameter	32.06 in (814.2 mm)	32.52 in (826.0 mm)	+0.46 in (+11.8 mm)	+1.45%
Sidewall height	7.03 in (178.5 mm)	6.26 in (159.0 mm)	−0.77 in (−19.5 mm)	−10.92%
Section width	10.04 in (255.0 mm)	10.43 in (265.0 mm)	+0.39 in (+10.0 mm)	+3.92%
Circumference	100.70 in (2,557.9 mm)	102.16 in (2,595.0 mm)	+1.46 in (+37.1 mm)	+1.45%
Revolutions per mile	629	620	−9	−1.43%

True speed with the speedometer calibrated for 255/70R18
Indicated	Actual on 255/70R18	Actual on 265/60R20	Difference
30 mph	30.0 mph	30.4 mph	+0.4 mph
60 mph	60.0 mph	60.9 mph	+0.9 mph
75 mph	75.0 mph	76.1 mph	+1.1 mph

Ride-height change: 265/60R20 raises the vehicle by 0.23 in (5.9 mm) at the axle (half the +11.8 mm diameter difference).

265/60R20 is 0.46 in taller than 255/70R18 and 10 mm wider, a 1.45% difference in overall diameter.

With the speedometer calibrated for 255/70R18, an indicated 60 mph is actually 60.9 mph on 265/60R20, and revolutions per mile change from 629 to 620.

265/60R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 255/70R18.

Size pages

Other comparisons with 255/70R18

Other comparisons with 265/60R20

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