Tire Size Box

205/50R18 vs 205/55R18

205/55R18 compared with 205/50R18

+3.1% diameter, 0.0" width

205/55R18 is 26.88" tall vs 26.07". More than the 3% rule of thumb, so check carefully before switching.

26.1"18" rim4.0"8.1" wide
205/50R18 (solid) compared with 205/55R18 (dashed outline), drawn to scale

With 205/55R18 tires, when your speedometer says 60 mph you are really going

61.9 mph

205/55R18 is +0.81 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

205/50R18205/55R18Difference%
Overall diameter26.07"26.88"+0.81"+3.1%
Section width8.07"8.07"0.00"0.0%
Sidewall height4.04"4.44"+0.40"+10.0%
Circumference81.90"84.44"+2.54"+3.1%
Revolutions per mile773.6750.4−23.2−3.0%

Speedometer difference

If your vehicle came with 205/50R18 and you fit 205/55R18, 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 mph61.9 mph+1.9 mph
65 mph67.0 mph+2.0 mph
70 mph72.2 mph+2.2 mph
75 mph77.3 mph+2.3 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 205/50R18 or 205/55R18?
205/55R18 is taller by 0.81 inches (26.88" vs 26.07"). 205/50R18 is the same width.
Can I replace 205/50R18 with 205/55R18?
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 205/55R18 change my speedometer?
When your speedometer reads 60 mph with 205/55R18 fitted (calibrated for 205/50R18), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.1%.
Will 205/55R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.40 inches of ground clearance at the axle.

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