TireSizesFinder

275/40R21 vs 285/40R21

285/40R21 is 0.31 in (8.0 mm) taller than 275/40R21, a +1.06% diameter difference. With the speedometer set for 275/40R21, an indicated 60 mph is 60.6 mph on 285/40R21.

Is this a safe swap?

Diameter difference +1.06%: within the ±3% guideline

By overall diameter alone, 285/40R21 falls inside the ±3% range commonly used as a guideline when replacing 275/40R21. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 275/40R21 (29.66 in) vs 285/40R21 (29.98 in)275/40R2129.66 in × 10.83 in285/40R2129.98 in × 11.22 in
Side profile and tread width, drawn to the same scale.
275/40R21 vs 285/40R21 differences
Measurement275/40R21285/40R21Difference% diff
Overall diameter29.66 in (753.4 mm)29.98 in (761.4 mm)+0.31 in (+8.0 mm)+1.06%
Sidewall height4.33 in (110.0 mm)4.49 in (114.0 mm)+0.16 in (+4.0 mm)+3.64%
Section width10.83 in (275.0 mm)11.22 in (285.0 mm)+0.39 in (+10.0 mm)+3.64%
Circumference93.18 in (2,366.9 mm)94.17 in (2,392.0 mm)+0.99 in (+25.1 mm)+1.06%
Revolutions per mile680673−7−1.05%
True speed with the speedometer calibrated for 275/40R21
IndicatedActual on 275/40R21Actual on 285/40R21Difference
30 mph30.0 mph30.3 mph+0.3 mph
60 mph60.0 mph60.6 mph+0.6 mph
75 mph75.0 mph75.8 mph+0.8 mph

Ride-height change: 285/40R21 raises the vehicle by 0.16 in (4.0 mm) at the axle (half the +8.0 mm diameter difference).

285/40R21 is 0.31 in taller than 275/40R21 and 10 mm wider, a 1.06% difference in overall diameter.

With the speedometer calibrated for 275/40R21, an indicated 60 mph is actually 60.6 mph on 285/40R21, and revolutions per mile change from 680 to 673.

Both sizes mount on 21-inch wheels.

Size pages

Other comparisons with 275/40R21

Other comparisons with 285/40R21

Source: Calculated from standard tire geometry formulas. Verified . How these numbers are calculated.