Tire Size Box

235/50R21 vs 235/55R21

235/55R21 compared with 235/50R21

+3.1% diameter, 0.0" width

235/55R21 is 31.18" tall vs 30.25". More than the 3% rule of thumb, so check carefully before switching.

30.3"21" rim4.6"9.3" wide
235/50R21 (solid) compared with 235/55R21 (dashed outline), drawn to scale

With 235/55R21 tires, when your speedometer says 60 mph you are really going

61.8 mph

235/55R21 is +0.93 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/50R21235/55R21Difference%
Overall diameter30.25"31.18"+0.93"+3.1%
Section width9.25"9.25"0.00"0.0%
Sidewall height4.63"5.09"+0.46"+10.0%
Circumference95.04"97.95"+2.91"+3.1%
Revolutions per mile666.7646.9−19.8−3.0%

Speedometer difference

If your vehicle came with 235/50R21 and you fit 235/55R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph30.9 mph+0.9 mph
40 mph41.2 mph+1.2 mph
50 mph51.5 mph+1.5 mph
60 mph61.8 mph+1.8 mph
65 mph67.0 mph+2.0 mph
70 mph72.1 mph+2.1 mph
75 mph77.3 mph+2.3 mph
80 mph82.4 mph+2.4 mph

Each size on its own

Questions

Which is bigger, 235/50R21 or 235/55R21?
235/55R21 is taller by 0.93 inches (31.18" vs 30.25"). 235/50R21 is the same width.
Can I replace 235/50R21 with 235/55R21?
It is not recommended without checking carefully. The diameter difference is +3.1%, 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 235/55R21 change my speedometer?
When your speedometer reads 60 mph with 235/55R21 fitted (calibrated for 235/50R21), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.1%.
Will 235/55R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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