285/70R18 vs 275/65R20

275/65R20 is 0.37 in (9.3 mm) taller than 285/70R18, a +1.09% diameter difference. With the speedometer set for 285/70R18, an indicated 60 mph is 60.7 mph on 275/65R20.

Is this a safe swap?

Diameter difference +1.09%: within the ±3% guideline

By overall diameter alone, 275/65R20 falls inside the ±3% range commonly used as a guideline when replacing 285/70R18. 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.

285/70R18 vs 275/65R20 differences
Measurement	285/70R18	275/65R20	Difference	% diff
Overall diameter	33.71 in (856.2 mm)	34.07 in (865.5 mm)	+0.37 in (+9.3 mm)	+1.09%
Sidewall height	7.85 in (199.5 mm)	7.04 in (178.8 mm)	−0.82 in (−20.7 mm)	−10.40%
Section width	11.22 in (285.0 mm)	10.83 in (275.0 mm)	−0.39 in (−10.0 mm)	−3.51%
Circumference	105.90 in (2,689.8 mm)	107.05 in (2,719.0 mm)	+1.15 in (+29.2 mm)	+1.09%
Revolutions per mile	598	592	−6	−1.07%

True speed with the speedometer calibrated for 285/70R18
Indicated	Actual on 285/70R18	Actual on 275/65R20	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.7 mph	+0.7 mph
75 mph	75.0 mph	75.8 mph	+0.8 mph

Ride-height change: 275/65R20 raises the vehicle by 0.18 in (4.6 mm) at the axle (half the +9.3 mm diameter difference).

275/65R20 is 0.37 in taller than 285/70R18 and 10 mm narrower, a 1.09% difference in overall diameter.

With the speedometer calibrated for 285/70R18, an indicated 60 mph is actually 60.7 mph on 275/65R20, and revolutions per mile change from 598 to 592.

275/65R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 285/70R18.

Size pages

Other comparisons with 285/70R18

Other comparisons with 275/65R20

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