Tire Size Box

225/50R18 vs 225/55R18

225/55R18 compared with 225/50R18

+3.3% diameter, 0.0" width

225/55R18 is 27.74" tall vs 26.86". More than the 3% rule of thumb, so check carefully before switching.

26.9"18" rim4.4"8.9" wide
225/50R18 (solid) compared with 225/55R18 (dashed outline), drawn to scale

With 225/55R18 tires, when your speedometer says 60 mph you are really going

62.0 mph

225/55R18 is +0.89 inches (+3.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

225/50R18225/55R18Difference%
Overall diameter26.86"27.74"+0.89"+3.3%
Section width8.86"8.86"0.00"0.0%
Sidewall height4.43"4.87"+0.44"+10.0%
Circumference84.38"87.16"+2.78"+3.3%
Revolutions per mile750.9726.9−24.0−3.2%

Speedometer difference

If your vehicle came with 225/50R18 and you fit 225/55R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph62.0 mph+2.0 mph
65 mph67.1 mph+2.1 mph
70 mph72.3 mph+2.3 mph
75 mph77.5 mph+2.5 mph
80 mph82.6 mph+2.6 mph

Each size on its own

Questions

Which is bigger, 225/50R18 or 225/55R18?
225/55R18 is taller by 0.89 inches (27.74" vs 26.86"). 225/50R18 is the same width.
Can I replace 225/50R18 with 225/55R18?
It is not recommended without checking carefully. The diameter difference is +3.3%, 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 225/55R18 change my speedometer?
When your speedometer reads 60 mph with 225/55R18 fitted (calibrated for 225/50R18), your real speed is 62.0 mph. Your odometer will under-count miles by about 3.3%.
Will 225/55R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.44 inches of ground clearance at the axle.

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