Tire Size Box

205/70R18 vs 225/70R18

225/70R18 compared with 205/70R18

+3.8% diameter, +0.8" width

225/70R18 is 30.40" tall vs 29.30". More than the 3% rule of thumb, so check carefully before switching.

29.3"18" rim5.6"8.1" wide
205/70R18 (solid) compared with 225/70R18 (dashed outline), drawn to scale

With 225/70R18 tires, when your speedometer says 60 mph you are really going

62.3 mph

225/70R18 is +1.10 inches (+3.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

205/70R18225/70R18Difference%
Overall diameter29.30"30.40"+1.10"+3.8%
Section width8.07"8.86"+0.79"+9.8%
Sidewall height5.65"6.20"+0.55"+9.8%
Circumference92.05"95.51"+3.46"+3.8%
Revolutions per mile688.4663.4−25.0−3.6%

Speedometer difference

If your vehicle came with 205/70R18 and you fit 225/70R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.1 mph+1.1 mph
40 mph41.5 mph+1.5 mph
50 mph51.9 mph+1.9 mph
60 mph62.3 mph+2.3 mph
65 mph67.4 mph+2.4 mph
70 mph72.6 mph+2.6 mph
75 mph77.8 mph+2.8 mph
80 mph83.0 mph+3.0 mph

Each size on its own

Questions

Which is bigger, 205/70R18 or 225/70R18?
225/70R18 is taller by 1.10 inches (30.40" vs 29.30"). 225/70R18 is wider by 0.79 inches.
Can I replace 205/70R18 with 225/70R18?
It is not recommended without checking carefully. The diameter difference is +3.8%, 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 225/70R18 change my speedometer?
When your speedometer reads 60 mph with 225/70R18 fitted (calibrated for 205/70R18), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.8%.
Will 225/70R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.55 inches of ground clearance at the axle.

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