Tire Size Box

285/50R20 vs 285/55R20

285/55R20 compared with 285/50R20

+3.6% diameter, 0.0" width

285/55R20 is 32.34" tall vs 31.22". More than the 3% rule of thumb, so check carefully before switching.

31.2"20" rim5.6"11.2" wide
285/50R20 (solid) compared with 285/55R20 (dashed outline), drawn to scale

With 285/55R20 tires, when your speedometer says 60 mph you are really going

62.2 mph

285/55R20 is +1.12 inches (+3.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/50R20285/55R20Difference%
Overall diameter31.22"32.34"+1.12"+3.6%
Section width11.22"11.22"0.00"0.0%
Sidewall height5.61"6.17"+0.56"+10.0%
Circumference98.08"101.61"+3.53"+3.6%
Revolutions per mile646.0623.6−22.4−3.5%

Speedometer difference

If your vehicle came with 285/50R20 and you fit 285/55R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.1 mph+1.1 mph
40 mph41.4 mph+1.4 mph
50 mph51.8 mph+1.8 mph
60 mph62.2 mph+2.2 mph
65 mph67.3 mph+2.3 mph
70 mph72.5 mph+2.5 mph
75 mph77.7 mph+2.7 mph
80 mph82.9 mph+2.9 mph

Each size on its own

Questions

Which is bigger, 285/50R20 or 285/55R20?
285/55R20 is taller by 1.12 inches (32.34" vs 31.22"). 285/50R20 is the same width.
Can I replace 285/50R20 with 285/55R20?
It is not recommended without checking carefully. The diameter difference is +3.6%, more than the 3% most shops and makers allow. It will throw off the speedometer and may affect ABS, stability control and clearance.
How much will 285/55R20 change my speedometer?
When your speedometer reads 60 mph with 285/55R20 fitted (calibrated for 285/50R20), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.6%.
Will 285/55R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.56 inches of ground clearance at the axle.

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