275/70R18 vs 275/65R20

275/65R20 is 0.92 in (23.3 mm) taller than 275/70R18, a +2.77% diameter difference. With the speedometer set for 275/70R18, an indicated 60 mph is 61.7 mph on 275/65R20.

Is this a safe swap?

Diameter difference +2.77%: within the ±3% guideline

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

275/70R18 vs 275/65R20 differences
Measurement	275/70R18	275/65R20	Difference	% diff
Overall diameter	33.16 in (842.2 mm)	34.07 in (865.5 mm)	+0.92 in (+23.3 mm)	+2.77%
Sidewall height	7.58 in (192.5 mm)	7.04 in (178.8 mm)	−0.54 in (−13.7 mm)	−7.14%
Section width	10.83 in (275.0 mm)	10.83 in (275.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	104.17 in (2,645.8 mm)	107.05 in (2,719.0 mm)	+2.88 in (+73.2 mm)	+2.77%
Revolutions per mile	608	592	−16	−2.69%

True speed with the speedometer calibrated for 275/70R18
Indicated	Actual on 275/70R18	Actual on 275/65R20	Difference
30 mph	30.0 mph	30.8 mph	+0.8 mph
60 mph	60.0 mph	61.7 mph	+1.7 mph
75 mph	75.0 mph	77.1 mph	+2.1 mph

Ride-height change: 275/65R20 raises the vehicle by 0.46 in (11.6 mm) at the axle (half the +23.3 mm diameter difference).

275/65R20 is 0.92 in taller than 275/70R18 and the same width, a 2.77% difference in overall diameter.

With the speedometer calibrated for 275/70R18, an indicated 60 mph is actually 61.7 mph on 275/65R20, and revolutions per mile change from 608 to 592.

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

Size pages

Other comparisons with 275/70R18

Other comparisons with 275/65R20

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