TireSizesFinder

275/45R20 vs 285/40R21

285/40R21 is 0.23 in (5.9 mm) taller than 275/45R20, a +0.78% diameter difference. With the speedometer set for 275/45R20, an indicated 60 mph is 60.5 mph on 285/40R21.

Is this a safe swap?

Diameter difference +0.78%: under 1%

By overall diameter alone, 285/40R21 is a near match for 275/45R20; the speedometer changes by less than 1%. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 275/45R20 (29.74 in) vs 285/40R21 (29.98 in)275/45R2029.74 in × 10.83 in285/40R2129.98 in × 11.22 in
Side profile and tread width, drawn to the same scale.
275/45R20 vs 285/40R21 differences
Measurement275/45R20285/40R21Difference% diff
Overall diameter29.74 in (755.5 mm)29.98 in (761.4 mm)+0.23 in (+5.9 mm)+0.78%
Sidewall height4.87 in (123.8 mm)4.49 in (114.0 mm)−0.38 in (−9.7 mm)−7.88%
Section width10.83 in (275.0 mm)11.22 in (285.0 mm)+0.39 in (+10.0 mm)+3.64%
Circumference93.44 in (2,373.5 mm)94.17 in (2,392.0 mm)+0.73 in (+18.5 mm)+0.78%
Revolutions per mile678673−5−0.77%
True speed with the speedometer calibrated for 275/45R20
IndicatedActual on 275/45R20Actual on 285/40R21Difference
30 mph30.0 mph30.2 mph+0.2 mph
60 mph60.0 mph60.5 mph+0.5 mph
75 mph75.0 mph75.6 mph+0.6 mph

Ride-height change: 285/40R21 raises the vehicle by 0.12 in (2.9 mm) at the axle (half the +5.9 mm diameter difference).

285/40R21 is 0.23 in taller than 275/45R20 and 10 mm wider, a 0.78% difference in overall diameter.

With the speedometer calibrated for 275/45R20, an indicated 60 mph is actually 60.5 mph on 285/40R21, and revolutions per mile change from 678 to 673.

285/40R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 275/45R20.

Size pages

Other comparisons with 275/45R20

Other comparisons with 285/40R21

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