265/45R18 vs 275/35R20

275/35R20 is 0.19 in (4.8 mm) taller than 265/45R18, a +0.69% diameter difference. With the speedometer set for 265/45R18, an indicated 60 mph is 60.4 mph on 275/35R20.

Is this a safe swap?

Diameter difference +0.69%: under 1%

By overall diameter alone, 275/35R20 is a near match for 265/45R18; 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.

265/45R18 vs 275/35R20 differences
Measurement	265/45R18	275/35R20	Difference	% diff
Overall diameter	27.39 in (695.7 mm)	27.58 in (700.5 mm)	+0.19 in (+4.8 mm)	+0.69%
Sidewall height	4.69 in (119.3 mm)	3.79 in (96.3 mm)	−0.91 in (−23.0 mm)	−19.29%
Section width	10.43 in (265.0 mm)	10.83 in (275.0 mm)	+0.39 in (+10.0 mm)	+3.77%
Circumference	86.05 in (2,185.6 mm)	86.64 in (2,200.7 mm)	+0.59 in (+15.1 mm)	+0.69%
Revolutions per mile	736	731	−5	−0.69%

True speed with the speedometer calibrated for 265/45R18
Indicated	Actual on 265/45R18	Actual on 275/35R20	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.4 mph	+0.4 mph
75 mph	75.0 mph	75.5 mph	+0.5 mph

Ride-height change: 275/35R20 raises the vehicle by 0.09 in (2.4 mm) at the axle (half the +4.8 mm diameter difference).

275/35R20 is 0.19 in taller than 265/45R18 and 10 mm wider, a 0.69% difference in overall diameter.

With the speedometer calibrated for 265/45R18, an indicated 60 mph is actually 60.4 mph on 275/35R20, and revolutions per mile change from 736 to 731.

275/35R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 265/45R18.

Size pages

Other comparisons with 265/45R18

Other comparisons with 275/35R20

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