275/45R21 vs 285/45R21

285/45R21 is 0.35 in (9.0 mm) taller than 275/45R21, a +1.15% diameter difference. With the speedometer set for 275/45R21, an indicated 60 mph is 60.7 mph on 285/45R21.

Is this a safe swap?

Diameter difference +1.15%: within the ±3% guideline

By overall diameter alone, 285/45R21 falls inside the ±3% range commonly used as a guideline when replacing 275/45R21. 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.

275/45R21 vs 285/45R21 differences
Measurement	275/45R21	285/45R21	Difference	% diff
Overall diameter	30.74 in (780.9 mm)	31.10 in (789.9 mm)	+0.35 in (+9.0 mm)	+1.15%
Sidewall height	4.87 in (123.8 mm)	5.05 in (128.3 mm)	+0.18 in (+4.5 mm)	+3.64%
Section width	10.83 in (275.0 mm)	11.22 in (285.0 mm)	+0.39 in (+10.0 mm)	+3.64%
Circumference	96.59 in (2,453.3 mm)	97.70 in (2,481.5 mm)	+1.11 in (+28.3 mm)	+1.15%
Revolutions per mile	656	649	−7	−1.14%

True speed with the speedometer calibrated for 275/45R21
Indicated	Actual on 275/45R21	Actual on 285/45R21	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	75.9 mph	+0.9 mph

Ride-height change: 285/45R21 raises the vehicle by 0.18 in (4.5 mm) at the axle (half the +9.0 mm diameter difference).

285/45R21 is 0.35 in taller than 275/45R21 and 10 mm wider, a 1.15% difference in overall diameter.

With the speedometer calibrated for 275/45R21, an indicated 60 mph is actually 60.7 mph on 285/45R21, and revolutions per mile change from 656 to 649.

Both sizes mount on 21-inch wheels.

Size pages

Other comparisons with 275/45R21

Other comparisons with 285/45R21

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