Tire Size Box

285/50R18 vs 285/55R18

285/55R18 compared with 285/50R18

+3.8% diameter, 0.0" width

285/55R18 is 30.34" tall vs 29.22". More than the 3% rule of thumb, so check carefully before switching.

29.2"18" rim5.6"11.2" wide
285/50R18 (solid) compared with 285/55R18 (dashed outline), drawn to scale

With 285/55R18 tires, when your speedometer says 60 mph you are really going

62.3 mph

285/55R18 is +1.12 inches (+3.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/50R18285/55R18Difference%
Overall diameter29.22"30.34"+1.12"+3.8%
Section width11.22"11.22"0.00"0.0%
Sidewall height5.61"6.17"+0.56"+10.0%
Circumference91.80"95.32"+3.53"+3.8%
Revolutions per mile690.2664.7−25.5−3.7%

Speedometer difference

If your vehicle came with 285/50R18 and you fit 285/55R18, 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 mph41.5 mph+1.5 mph
50 mph51.9 mph+1.9 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, 285/50R18 or 285/55R18?
285/55R18 is taller by 1.12 inches (30.34" vs 29.22"). 285/50R18 is the same width.
Can I replace 285/50R18 with 285/55R18?
It is not recommended without checking carefully. The diameter difference is +3.8%, 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 285/55R18 change my speedometer?
When your speedometer reads 60 mph with 285/55R18 fitted (calibrated for 285/50R18), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.8%.
Will 285/55R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.56 inches of ground clearance at the axle.

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