235/35R20 vs 275/30R20

275/30R20 is 0.02 in (0.5 mm) taller than 235/35R20, a +0.07% diameter difference. With the speedometer set for 235/35R20, an indicated 60 mph is 60.0 mph on 275/30R20.

Is this a safe swap?

Diameter difference +0.07%: under 1%

By overall diameter alone, 275/30R20 is a near match for 235/35R20; 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.

235/35R20 vs 275/30R20 differences
Measurement	235/35R20	275/30R20	Difference	% diff
Overall diameter	26.48 in (672.5 mm)	26.50 in (673.0 mm)	+0.02 in (+0.5 mm)	+0.07%
Sidewall height	3.24 in (82.3 mm)	3.25 in (82.5 mm)	+0.01 in (+0.3 mm)	+0.30%
Section width	9.25 in (235.0 mm)	10.83 in (275.0 mm)	+1.57 in (+40.0 mm)	+17.02%
Circumference	83.18 in (2,112.7 mm)	83.24 in (2,114.3 mm)	+0.06 in (+1.6 mm)	+0.07%
Revolutions per mile	762	761	−1	−0.07%

True speed with the speedometer calibrated for 235/35R20
Indicated	Actual on 235/35R20	Actual on 275/30R20	Difference
30 mph	30.0 mph	30.0 mph	0.0 mph
60 mph	60.0 mph	60.0 mph	0.0 mph
75 mph	75.0 mph	75.1 mph	+0.1 mph

Ride-height change: 275/30R20 raises the vehicle by 0.01 in (0.3 mm) at the axle (half the +0.5 mm diameter difference).

275/30R20 is 0.02 in taller than 235/35R20 and 40 mm wider, a 0.07% difference in overall diameter.

With the speedometer calibrated for 235/35R20, an indicated 60 mph is actually 60.0 mph on 275/30R20, and revolutions per mile change from 762 to 761.

Both sizes mount on 20-inch wheels.

Size pages

Other comparisons with 235/35R20

Other comparisons with 275/30R20

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