255/45R18 vs 265/35R20

265/35R20 is 0.27 in (6.8 mm) taller than 255/45R18, a +0.99% diameter difference. With the speedometer set for 255/45R18, an indicated 60 mph is 60.6 mph on 265/35R20.

Is this a safe swap?

Diameter difference +0.99%: under 1%

By overall diameter alone, 265/35R20 is a near match for 255/45R18; 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.

255/45R18 vs 265/35R20 differences
Measurement	255/45R18	265/35R20	Difference	% diff
Overall diameter	27.04 in (686.7 mm)	27.30 in (693.5 mm)	+0.27 in (+6.8 mm)	+0.99%
Sidewall height	4.52 in (114.8 mm)	3.65 in (92.8 mm)	−0.87 in (−22.0 mm)	−19.17%
Section width	10.04 in (255.0 mm)	10.43 in (265.0 mm)	+0.39 in (+10.0 mm)	+3.92%
Circumference	84.93 in (2,157.3 mm)	85.78 in (2,178.7 mm)	+0.84 in (+21.4 mm)	+0.99%
Revolutions per mile	746	739	−7	−0.98%

True speed with the speedometer calibrated for 255/45R18
Indicated	Actual on 255/45R18	Actual on 265/35R20	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.6 mph	+0.6 mph
75 mph	75.0 mph	75.7 mph	+0.7 mph

Ride-height change: 265/35R20 raises the vehicle by 0.13 in (3.4 mm) at the axle (half the +6.8 mm diameter difference).

265/35R20 is 0.27 in taller than 255/45R18 and 10 mm wider, a 0.99% difference in overall diameter.

With the speedometer calibrated for 255/45R18, an indicated 60 mph is actually 60.6 mph on 265/35R20, and revolutions per mile change from 746 to 739.

265/35R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 255/45R18.

Size pages

Other comparisons with 255/45R18

Other comparisons with 265/35R20

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