Tire Size Box

285/45R18 vs 285/55R18

285/55R18 compared with 285/45R18

+8.0% diameter, 0.0" width

285/55R18 is 30.34" tall vs 28.10". More than the 3% rule of thumb, so check carefully before switching.

28.1"18" rim5.0"11.2" wide
285/45R18 (solid) compared with 285/55R18 (dashed outline), drawn to scale

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

64.8 mph

285/55R18 is +2.24 inches (+8.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/45R18285/55R18Difference%
Overall diameter28.10"30.34"+2.24"+8.0%
Section width11.22"11.22"0.00"0.0%
Sidewall height5.05"6.17"+1.12"+22.2%
Circumference88.27"95.32"+7.05"+8.0%
Revolutions per mile717.8664.7−53.1−7.4%

Speedometer difference

If your vehicle came with 285/45R18 and you fit 285/55R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.6 mph+1.6 mph
30 mph32.4 mph+2.4 mph
40 mph43.2 mph+3.2 mph
50 mph54.0 mph+4.0 mph
60 mph64.8 mph+4.8 mph
65 mph70.2 mph+5.2 mph
70 mph75.6 mph+5.6 mph
75 mph81.0 mph+6.0 mph
80 mph86.4 mph+6.4 mph

Each size on its own

Questions

Which is bigger, 285/45R18 or 285/55R18?
285/55R18 is taller by 2.24 inches (30.34" vs 28.10"). 285/45R18 is the same width.
Can I replace 285/45R18 with 285/55R18?
It is not recommended without checking carefully. The diameter difference is +8.0%, 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 285/45R18), your real speed is 64.8 mph. Your odometer will under-count miles by about 8.0%.
Will 285/55R18 lift my vehicle?
Ride height changes by half the diameter difference: +1.12 inches of ground clearance at the axle.

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