Tire Size Box

325/60R18 vs 325/65R18

325/65R18 compared with 325/60R18

+3.8% diameter, 0.0" width

325/65R18 is 34.63" tall vs 33.35". More than the 3% rule of thumb, so check carefully before switching.

33.4"18" rim7.7"12.8" wide
325/60R18 (solid) compared with 325/65R18 (dashed outline), drawn to scale

With 325/65R18 tires, when your speedometer says 60 mph you are really going

62.3 mph

325/65R18 is +1.28 inches (+3.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

325/60R18325/65R18Difference%
Overall diameter33.35"34.63"+1.28"+3.8%
Section width12.80"12.80"0.00"0.0%
Sidewall height7.68"8.32"+0.64"+8.3%
Circumference104.79"108.81"+4.02"+3.8%
Revolutions per mile604.7582.3−22.3−3.7%

Speedometer difference

If your vehicle came with 325/60R18 and you fit 325/65R18, 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 mph41.5 mph+1.5 mph
50 mph51.9 mph+1.9 mph
60 mph62.3 mph+2.3 mph
65 mph67.5 mph+2.5 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, 325/60R18 or 325/65R18?
325/65R18 is taller by 1.28 inches (34.63" vs 33.35"). 325/60R18 is the same width.
Can I replace 325/60R18 with 325/65R18?
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 325/65R18 change my speedometer?
When your speedometer reads 60 mph with 325/65R18 fitted (calibrated for 325/60R18), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.8%.
Will 325/65R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.64 inches of ground clearance at the axle.

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