Tire Size Box

225/65R17 vs 205/65R18

205/65R18 compared with 225/65R17

−0.1% diameter, −0.8" width

205/65R18 is 28.49" tall vs 28.52". Within the 3% rule, so usually interchangeable.

28.5"17" rim5.8"8.9" wide
225/65R17 (solid) compared with 205/65R18 (dashed outline), drawn to scale

With 205/65R18 tires, when your speedometer says 60 mph you are really going

60.0 mph

205/65R18 is −0.02 inches (−0.1%) in overall diameter. That is within the 3% most shops and makers allow.

225/65R17205/65R18Difference%
Overall diameter28.52"28.49"−0.02"−0.1%
Section width8.86"8.07"−0.79"−8.9%
Sidewall height5.76"5.25"−0.51"−8.9%
Circumference89.58"89.51"−0.07"−0.1%
Revolutions per mile707.3707.8+0.6+0.1%

Speedometer difference

If your vehicle came with 225/65R17 and you fit 205/65R18, 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 mph60.0 mph0.0 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, 225/65R17 or 205/65R18?
225/65R17 is taller by 0.02 inches (28.52" vs 28.49"). 225/65R17 is wider by 0.79 inches.
Can I replace 225/65R17 with 205/65R18?
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 205/65R18 change my speedometer?
When your speedometer reads 60 mph with 205/65R18 fitted (calibrated for 225/65R17), your real speed is 60.0 mph. Your odometer will over-count miles by about 0.1%.
Will 205/65R18 lift my vehicle?
Ride height changes by half the diameter difference: −0.01 inches of ground clearance at the axle.

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