Tire Size Box

275/50R18 vs 285/50R18

285/50R18 compared with 275/50R18

+1.4% diameter, +0.4" width

285/50R18 is 29.22" tall vs 28.83". Within the 3% rule, so usually interchangeable.

28.8"18" rim5.4"10.8" wide
275/50R18 (solid) compared with 285/50R18 (dashed outline), drawn to scale

With 285/50R18 tires, when your speedometer says 60 mph you are really going

60.8 mph

285/50R18 is +0.39 inches (+1.4%) in overall diameter. That is within the 3% most shops and makers allow.

275/50R18285/50R18Difference%
Overall diameter28.83"29.22"+0.39"+1.4%
Section width10.83"11.22"+0.39"+3.6%
Sidewall height5.41"5.61"+0.20"+3.6%
Circumference90.56"91.80"+1.24"+1.4%
Revolutions per mile699.6690.2−9.4−1.3%

Speedometer difference

If your vehicle came with 275/50R18 and you fit 285/50R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.3 mph+0.3 mph
30 mph30.4 mph+0.4 mph
40 mph40.5 mph+0.5 mph
50 mph50.7 mph+0.7 mph
60 mph60.8 mph+0.8 mph
65 mph65.9 mph+0.9 mph
70 mph71.0 mph+1.0 mph
75 mph76.0 mph+1.0 mph
80 mph81.1 mph+1.1 mph

Each size on its own

Questions

Which is bigger, 275/50R18 or 285/50R18?
285/50R18 is taller by 0.39 inches (29.22" vs 28.83"). 285/50R18 is wider by 0.39 inches.
Can I replace 275/50R18 with 285/50R18?
Usually, yes. The diameter difference is +1.4%, inside the 3% rule of thumb most tire shops use. Check that the wider or taller tire clears your suspension and fenders, and that its load index meets your placard.
How much will 285/50R18 change my speedometer?
When your speedometer reads 60 mph with 285/50R18 fitted (calibrated for 275/50R18), your real speed is 60.8 mph. Your odometer will under-count miles by about 1.4%.
Will 285/50R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.20 inches of ground clearance at the axle.

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