Tire Size Box

205/55R18 vs 225/55R18

225/55R18 compared with 205/55R18

+3.2% diameter, +0.8" width

225/55R18 is 27.74" tall vs 26.88". More than the 3% rule of thumb, so check carefully before switching.

26.9"18" rim4.4"8.1" wide
205/55R18 (solid) compared with 225/55R18 (dashed outline), drawn to scale

With 225/55R18 tires, when your speedometer says 60 mph you are really going

61.9 mph

225/55R18 is +0.87 inches (+3.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

205/55R18225/55R18Difference%
Overall diameter26.88"27.74"+0.87"+3.2%
Section width8.07"8.86"+0.79"+9.8%
Sidewall height4.44"4.87"+0.43"+9.8%
Circumference84.44"87.16"+2.72"+3.2%
Revolutions per mile750.4726.9−23.4−3.1%

Speedometer difference

If your vehicle came with 205/55R18 and you fit 225/55R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph31.0 mph+1.0 mph
40 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.1 mph+2.1 mph
70 mph72.3 mph+2.3 mph
75 mph77.4 mph+2.4 mph
80 mph82.6 mph+2.6 mph

Each size on its own

Questions

Which is bigger, 205/55R18 or 225/55R18?
225/55R18 is taller by 0.87 inches (27.74" vs 26.88"). 225/55R18 is wider by 0.79 inches.
Can I replace 205/55R18 with 225/55R18?
It is not recommended without checking carefully. The diameter difference is +3.2%, 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 225/55R18 change my speedometer?
When your speedometer reads 60 mph with 225/55R18 fitted (calibrated for 205/55R18), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.2%.
Will 225/55R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.43 inches of ground clearance at the axle.

Other comparisons