Tire Size Box

285/45R21 vs 285/50R21

285/50R21 compared with 285/45R21

+3.6% diameter, 0.0" width

285/50R21 is 32.22" tall vs 31.10". More than the 3% rule of thumb, so check carefully before switching.

31.1"21" rim5.0"11.2" wide
285/45R21 (solid) compared with 285/50R21 (dashed outline), drawn to scale

With 285/50R21 tires, when your speedometer says 60 mph you are really going

62.2 mph

285/50R21 is +1.12 inches (+3.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/45R21285/50R21Difference%
Overall diameter31.10"32.22"+1.12"+3.6%
Section width11.22"11.22"0.00"0.0%
Sidewall height5.05"5.61"+0.56"+11.1%
Circumference97.70"101.22"+3.53"+3.6%
Revolutions per mile648.5625.9−22.6−3.5%

Speedometer difference

If your vehicle came with 285/45R21 and you fit 285/50R21, 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, 285/45R21 or 285/50R21?
285/50R21 is taller by 1.12 inches (32.22" vs 31.10"). 285/45R21 is the same width.
Can I replace 285/45R21 with 285/50R21?
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 285/50R21 change my speedometer?
When your speedometer reads 60 mph with 285/50R21 fitted (calibrated for 285/45R21), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.6%.
Will 285/50R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.56 inches of ground clearance at the axle.

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