Tire Size Box

325/55R18 vs 325/60R18

325/60R18 compared with 325/55R18

+4.0% diameter, 0.0" width

325/60R18 is 33.35" tall vs 32.07". More than the 3% rule of thumb, so check carefully before switching.

32.1"18" rim7.0"12.8" wide
325/55R18 (solid) compared with 325/60R18 (dashed outline), drawn to scale

With 325/60R18 tires, when your speedometer says 60 mph you are really going

62.4 mph

325/60R18 is +1.28 inches (+4.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

325/55R18325/60R18Difference%
Overall diameter32.07"33.35"+1.28"+4.0%
Section width12.80"12.80"0.00"0.0%
Sidewall height7.04"7.68"+0.64"+9.1%
Circumference100.77"104.79"+4.02"+4.0%
Revolutions per mile628.8604.7−24.1−3.8%

Speedometer difference

If your vehicle came with 325/55R18 and you fit 325/60R18, 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 mph72.8 mph+2.8 mph
75 mph78.0 mph+3.0 mph
80 mph83.2 mph+3.2 mph

Each size on its own

Questions

Which is bigger, 325/55R18 or 325/60R18?
325/60R18 is taller by 1.28 inches (33.35" vs 32.07"). 325/55R18 is the same width.
Can I replace 325/55R18 with 325/60R18?
It is not recommended without checking carefully. The diameter difference is +4.0%, 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 325/60R18 change my speedometer?
When your speedometer reads 60 mph with 325/60R18 fitted (calibrated for 325/55R18), your real speed is 62.4 mph. Your odometer will under-count miles by about 4.0%.
Will 325/60R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.64 inches of ground clearance at the axle.

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