Tire Size Box

205/55R17 vs 285/35R18

285/35R18 compared with 205/55R17

−0.1% diameter, +3.1" width

285/35R18 is 25.85" tall vs 25.88". Within the 3% rule, so usually interchangeable.

25.9"17" rim4.4"8.1" wide
205/55R17 (solid) compared with 285/35R18 (dashed outline), drawn to scale

With 285/35R18 tires, when your speedometer says 60 mph you are really going

59.9 mph

285/35R18 is −0.02 inches (−0.1%) in overall diameter. That is within the 3% most shops and makers allow.

205/55R17285/35R18Difference%
Overall diameter25.88"25.85"−0.02"−0.1%
Section width8.07"11.22"+3.15"+39.0%
Sidewall height4.44"3.93"−0.51"−11.5%
Circumference81.30"81.22"−0.07"−0.1%
Revolutions per mile779.4780.1+0.7+0.1%

Speedometer difference

If your vehicle came with 205/55R17 and you fit 285/35R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.0 mph0.0 mph
30 mph30.0 mph0.0 mph
40 mph40.0 mph0.0 mph
50 mph50.0 mph0.0 mph
60 mph59.9 mph−0.1 mph
65 mph64.9 mph−0.1 mph
70 mph69.9 mph−0.1 mph
75 mph74.9 mph−0.1 mph
80 mph79.9 mph−0.1 mph

Each size on its own

Questions

Which is bigger, 205/55R17 or 285/35R18?
205/55R17 is taller by 0.02 inches (25.88" vs 25.85"). 285/35R18 is wider by 3.15 inches.
Can I replace 205/55R17 with 285/35R18?
Usually, yes. The diameter difference is −0.1%, 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 285/35R18 change my speedometer?
When your speedometer reads 60 mph with 285/35R18 fitted (calibrated for 205/55R17), your real speed is 59.9 mph. Your odometer will over-count miles by about 0.1%.
Will 285/35R18 lift my vehicle?
Ride height changes by half the diameter difference: −0.01 inches of ground clearance at the axle.

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