TireSizesFinder

265/55R20 vs 285/45R21

285/45R21 is 0.38 in (9.6 mm) shorter than 265/55R20, a −1.20% diameter difference. With the speedometer set for 265/55R20, an indicated 60 mph is 59.3 mph on 285/45R21.

Is this a safe swap?

Diameter difference −1.20%: within the ±3% guideline

By overall diameter alone, 285/45R21 falls inside the ±3% range commonly used as a guideline when replacing 265/55R20. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

To-scale drawing: 265/55R20 (31.48 in) vs 285/45R21 (31.10 in)265/55R2031.48 in × 10.43 in285/45R2131.10 in × 11.22 in
Side profile and tread width, drawn to the same scale.
265/55R20 vs 285/45R21 differences
Measurement265/55R20285/45R21Difference% diff
Overall diameter31.48 in (799.5 mm)31.10 in (789.9 mm)−0.38 in (−9.6 mm)−1.20%
Sidewall height5.74 in (145.8 mm)5.05 in (128.3 mm)−0.69 in (−17.5 mm)−12.01%
Section width10.43 in (265.0 mm)11.22 in (285.0 mm)+0.79 in (+20.0 mm)+7.55%
Circumference98.89 in (2,511.7 mm)97.70 in (2,481.5 mm)−1.19 in (−30.2 mm)−1.20%
Revolutions per mile641649+8+1.22%
True speed with the speedometer calibrated for 265/55R20
IndicatedActual on 265/55R20Actual on 285/45R21Difference
30 mph30.0 mph29.6 mph−0.4 mph
60 mph60.0 mph59.3 mph−0.7 mph
75 mph75.0 mph74.1 mph−0.9 mph

Ride-height change: 285/45R21 lowers the vehicle by 0.19 in (4.8 mm) at the axle (half the −9.6 mm diameter difference).

285/45R21 is 0.38 in shorter than 265/55R20 and 20 mm wider, a 1.20% difference in overall diameter.

With the speedometer calibrated for 265/55R20, an indicated 60 mph is actually 59.3 mph on 285/45R21, and revolutions per mile change from 641 to 649.

285/45R21 mounts on a 21-inch wheel, a plus-1 fitment from the 20-inch wheel of 265/55R20.

Size pages

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