275/30R21 vs 275/35R21

275/35R21 is 1.08 in (27.5 mm) taller than 275/30R21, a +3.94% diameter difference. With the speedometer set for 275/30R21, an indicated 60 mph is 62.4 mph on 275/35R21.

Is this a safe swap?

Diameter difference +3.94%: outside the ±3% guideline

By overall diameter alone, 275/35R21 falls outside the ±3% range commonly used as a guideline when replacing 275/30R21; speedometer and ride-height changes are larger. 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.

275/30R21 vs 275/35R21 differences
Measurement	275/30R21	275/35R21	Difference	% diff
Overall diameter	27.50 in (698.4 mm)	28.58 in (725.9 mm)	+1.08 in (+27.5 mm)	+3.94%
Sidewall height	3.25 in (82.5 mm)	3.79 in (96.3 mm)	+0.54 in (+13.8 mm)	+16.67%
Section width	10.83 in (275.0 mm)	10.83 in (275.0 mm)	0.00 in (0.0 mm)	0.00%
Circumference	86.38 in (2,194.1 mm)	89.78 in (2,280.5 mm)	+3.40 in (+86.4 mm)	+3.94%
Revolutions per mile	733	706	−28	−3.79%

True speed with the speedometer calibrated for 275/30R21
Indicated	Actual on 275/30R21	Actual on 275/35R21	Difference
30 mph	30.0 mph	31.2 mph	+1.2 mph
60 mph	60.0 mph	62.4 mph	+2.4 mph
75 mph	75.0 mph	78.0 mph	+3.0 mph

Ride-height change: 275/35R21 raises the vehicle by 0.54 in (13.8 mm) at the axle (half the +27.5 mm diameter difference).

275/35R21 is 1.08 in taller than 275/30R21 and the same width, a 3.94% difference in overall diameter.

With the speedometer calibrated for 275/30R21, an indicated 60 mph is actually 62.4 mph on 275/35R21, and revolutions per mile change from 733 to 706.

Both sizes mount on 21-inch wheels.

Size pages

Other comparisons with 275/30R21

Other comparisons with 275/35R21

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