Tire Size Box

285/45R20 vs 285/50R20

285/50R20 compared with 285/45R20

+3.7% diameter, 0.0" width

285/50R20 is 31.22" tall vs 30.10". More than the 3% rule of thumb, so check carefully before switching.

30.1"20" rim5.0"11.2" wide
285/45R20 (solid) compared with 285/50R20 (dashed outline), drawn to scale

With 285/50R20 tires, when your speedometer says 60 mph you are really going

62.2 mph

285/50R20 is +1.12 inches (+3.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/45R20285/50R20Difference%
Overall diameter30.10"31.22"+1.12"+3.7%
Section width11.22"11.22"0.00"0.0%
Sidewall height5.05"5.61"+0.56"+11.1%
Circumference94.56"98.08"+3.53"+3.7%
Revolutions per mile670.1646.0−24.1−3.6%

Speedometer difference

If your vehicle came with 285/45R20 and you fit 285/50R20, 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 mph41.5 mph+1.5 mph
50 mph51.9 mph+1.9 mph
60 mph62.2 mph+2.2 mph
65 mph67.4 mph+2.4 mph
70 mph72.6 mph+2.6 mph
75 mph77.8 mph+2.8 mph
80 mph83.0 mph+3.0 mph

Each size on its own

Questions

Which is bigger, 285/45R20 or 285/50R20?
285/50R20 is taller by 1.12 inches (31.22" vs 30.10"). 285/45R20 is the same width.
Can I replace 285/45R20 with 285/50R20?
It is not recommended without checking carefully. The diameter difference is +3.7%, 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 285/50R20 change my speedometer?
When your speedometer reads 60 mph with 285/50R20 fitted (calibrated for 285/45R20), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.7%.
Will 285/50R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.56 inches of ground clearance at the axle.

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