265/65R18 vs 285/50R20

285/50R20 is 0.34 in (8.7 mm) shorter than 265/65R18, a −1.09% diameter difference. With the speedometer set for 265/65R18, an indicated 60 mph is 59.3 mph on 285/50R20.

Is this a safe swap?

Diameter difference −1.09%: within the ±3% guideline

By overall diameter alone, 285/50R20 falls inside the ±3% range commonly used as a guideline when replacing 265/65R18. 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.

265/65R18 vs 285/50R20 differences
Measurement	265/65R18	285/50R20	Difference	% diff
Overall diameter	31.56 in (801.7 mm)	31.22 in (793.0 mm)	−0.34 in (−8.7 mm)	−1.09%
Sidewall height	6.78 in (172.3 mm)	5.61 in (142.5 mm)	−1.17 in (−29.7 mm)	−17.27%
Section width	10.43 in (265.0 mm)	11.22 in (285.0 mm)	+0.79 in (+20.0 mm)	+7.55%
Circumference	99.16 in (2,518.6 mm)	98.08 in (2,491.3 mm)	−1.08 in (−27.3 mm)	−1.09%
Revolutions per mile	639	646	+7	+1.10%

True speed with the speedometer calibrated for 265/65R18
Indicated	Actual on 265/65R18	Actual on 285/50R20	Difference
30 mph	30.0 mph	29.7 mph	−0.3 mph
60 mph	60.0 mph	59.3 mph	−0.7 mph
75 mph	75.0 mph	74.2 mph	−0.8 mph

Ride-height change: 285/50R20 lowers the vehicle by 0.17 in (4.4 mm) at the axle (half the −8.7 mm diameter difference).

285/50R20 is 0.34 in shorter than 265/65R18 and 20 mm wider, a 1.09% difference in overall diameter.

With the speedometer calibrated for 265/65R18, an indicated 60 mph is actually 59.3 mph on 285/50R20, and revolutions per mile change from 639 to 646.

285/50R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 265/65R18.

Size pages

Other comparisons with 265/65R18

Other comparisons with 285/50R20

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