TireSizesFinder

285/60R18 vs 285/50R20

285/50R20 is 0.24 in (6.2 mm) shorter than 285/60R18, a −0.78% diameter difference. With the speedometer set for 285/60R18, an indicated 60 mph is 59.5 mph on 285/50R20.

Is this a safe swap?

Diameter difference −0.78%: under 1%

By overall diameter alone, 285/50R20 is a near match for 285/60R18; 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: 285/60R18 (31.46 in) vs 285/50R20 (31.22 in)285/60R1831.46 in × 11.22 in285/50R2031.22 in × 11.22 in
Side profile and tread width, drawn to the same scale.
285/60R18 vs 285/50R20 differences
Measurement285/60R18285/50R20Difference% diff
Overall diameter31.46 in (799.2 mm)31.22 in (793.0 mm)−0.24 in (−6.2 mm)−0.78%
Sidewall height6.73 in (171.0 mm)5.61 in (142.5 mm)−1.12 in (−28.5 mm)−16.67%
Section width11.22 in (285.0 mm)11.22 in (285.0 mm)0.00 in (0.0 mm)0.00%
Circumference98.85 in (2,510.8 mm)98.08 in (2,491.3 mm)−0.77 in (−19.5 mm)−0.78%
Revolutions per mile641646+5+0.78%
True speed with the speedometer calibrated for 285/60R18
IndicatedActual on 285/60R18Actual on 285/50R20Difference
30 mph30.0 mph29.8 mph−0.2 mph
60 mph60.0 mph59.5 mph−0.5 mph
75 mph75.0 mph74.4 mph−0.6 mph

Ride-height change: 285/50R20 lowers the vehicle by 0.12 in (3.1 mm) at the axle (half the −6.2 mm diameter difference).

285/50R20 is 0.24 in shorter than 285/60R18 and the same width, a 0.78% difference in overall diameter.

With the speedometer calibrated for 285/60R18, an indicated 60 mph is actually 59.5 mph on 285/50R20, and revolutions per mile change from 641 to 646.

285/50R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 285/60R18.

Size pages

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Other comparisons with 285/50R20

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