Tire Size Box

205/75R18 vs 225/75R18

225/75R18 compared with 205/75R18

+3.9% diameter, +0.8" width

225/75R18 is 31.29" tall vs 30.11". More than the 3% rule of thumb, so check carefully before switching.

30.1"18" rim6.1"8.1" wide
205/75R18 (solid) compared with 225/75R18 (dashed outline), drawn to scale

With 225/75R18 tires, when your speedometer says 60 mph you are really going

62.4 mph

225/75R18 is +1.18 inches (+3.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

205/75R18225/75R18Difference%
Overall diameter30.11"31.29"+1.18"+3.9%
Section width8.07"8.86"+0.79"+9.8%
Sidewall height6.05"6.64"+0.59"+9.8%
Circumference94.58"98.29"+3.71"+3.9%
Revolutions per mile669.9644.6−25.3−3.8%

Speedometer difference

If your vehicle came with 205/75R18 and you fit 225/75R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.6 mph+1.6 mph
50 mph52.0 mph+2.0 mph
60 mph62.4 mph+2.4 mph
65 mph67.6 mph+2.6 mph
70 mph72.7 mph+2.7 mph
75 mph77.9 mph+2.9 mph
80 mph83.1 mph+3.1 mph

Each size on its own

Questions

Which is bigger, 205/75R18 or 225/75R18?
225/75R18 is taller by 1.18 inches (31.29" vs 30.11"). 225/75R18 is wider by 0.79 inches.
Can I replace 205/75R18 with 225/75R18?
It is not recommended without checking carefully. The diameter difference is +3.9%, 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 225/75R18 change my speedometer?
When your speedometer reads 60 mph with 225/75R18 fitted (calibrated for 205/75R18), your real speed is 62.4 mph. Your odometer will under-count miles by about 3.9%.
Will 225/75R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.59 inches of ground clearance at the axle.

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