Tire Size Box

185/50R15 vs 185/55R15

185/55R15 compared with 185/50R15

+3.3% diameter, 0.0" width

185/55R15 is 23.01" tall vs 22.28". More than the 3% rule of thumb, so check carefully before switching.

22.3"15" rim3.6"7.3" wide
185/50R15 (solid) compared with 185/55R15 (dashed outline), drawn to scale

With 185/55R15 tires, when your speedometer says 60 mph you are really going

62.0 mph

185/55R15 is +0.73 inches (+3.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

185/50R15185/55R15Difference%
Overall diameter22.28"23.01"+0.73"+3.3%
Section width7.28"7.28"0.00"0.0%
Sidewall height3.64"4.01"+0.36"+10.0%
Circumference70.01"72.29"+2.29"+3.3%
Revolutions per mile905.1876.4−28.6−3.2%

Speedometer difference

If your vehicle came with 185/50R15 and you fit 185/55R15, 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, 185/50R15 or 185/55R15?
185/55R15 is taller by 0.73 inches (23.01" vs 22.28"). 185/50R15 is the same width.
Can I replace 185/50R15 with 185/55R15?
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 185/55R15 change my speedometer?
When your speedometer reads 60 mph with 185/55R15 fitted (calibrated for 185/50R15), your real speed is 62.0 mph. Your odometer will under-count miles by about 3.3%.
Will 185/55R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.36 inches of ground clearance at the axle.

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