Tire Size Box

285/40R21 vs 285/50R21

285/50R21 compared with 285/40R21

+7.5% diameter, 0.0" width

285/50R21 is 32.22" tall vs 29.98". More than the 3% rule of thumb, so check carefully before switching.

30.0"21" rim4.5"11.2" wide
285/40R21 (solid) compared with 285/50R21 (dashed outline), drawn to scale

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

64.5 mph

285/50R21 is +2.24 inches (+7.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/40R21285/50R21Difference%
Overall diameter29.98"32.22"+2.24"+7.5%
Section width11.22"11.22"0.00"0.0%
Sidewall height4.49"5.61"+1.12"+25.0%
Circumference94.17"101.22"+7.05"+7.5%
Revolutions per mile672.8625.9−46.9−7.0%

Speedometer difference

If your vehicle came with 285/40R21 and you fit 285/50R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.5 mph+1.5 mph
30 mph32.2 mph+2.2 mph
40 mph43.0 mph+3.0 mph
50 mph53.7 mph+3.7 mph
60 mph64.5 mph+4.5 mph
65 mph69.9 mph+4.9 mph
70 mph75.2 mph+5.2 mph
75 mph80.6 mph+5.6 mph
80 mph86.0 mph+6.0 mph

Each size on its own

Questions

Which is bigger, 285/40R21 or 285/50R21?
285/50R21 is taller by 2.24 inches (32.22" vs 29.98"). 285/40R21 is the same width.
Can I replace 285/40R21 with 285/50R21?
It is not recommended without checking carefully. The diameter difference is +7.5%, 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 285/40R21), your real speed is 64.5 mph. Your odometer will under-count miles by about 7.5%.
Will 285/50R21 lift my vehicle?
Ride height changes by half the diameter difference: +1.12 inches of ground clearance at the axle.

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