Tire Size Box

165/55R15 vs 185/55R15

185/55R15 compared with 165/55R15

+3.9% diameter, +0.8" width

185/55R15 is 23.01" tall vs 22.15". More than the 3% rule of thumb, so check carefully before switching.

22.1"15" rim3.6"6.5" wide
165/55R15 (solid) compared with 185/55R15 (dashed outline), drawn to scale

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

62.3 mph

185/55R15 is +0.87 inches (+3.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

165/55R15185/55R15Difference%
Overall diameter22.15"23.01"+0.87"+3.9%
Section width6.50"7.28"+0.79"+12.1%
Sidewall height3.57"4.01"+0.43"+12.1%
Circumference69.57"72.29"+2.72"+3.9%
Revolutions per mile910.7876.4−34.3−3.8%

Speedometer difference

If your vehicle came with 165/55R15 and you fit 185/55R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.6 mph+1.6 mph
50 mph52.0 mph+2.0 mph
60 mph62.3 mph+2.3 mph
65 mph67.5 mph+2.5 mph
70 mph72.7 mph+2.7 mph
75 mph77.9 mph+2.9 mph
80 mph83.1 mph+3.1 mph

Each size on its own

Questions

Which is bigger, 165/55R15 or 185/55R15?
185/55R15 is taller by 0.87 inches (23.01" vs 22.15"). 185/55R15 is wider by 0.79 inches.
Can I replace 165/55R15 with 185/55R15?
It is not recommended without checking carefully. The diameter difference is +3.9%, 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 165/55R15), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.9%.
Will 185/55R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.43 inches of ground clearance at the axle.

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