Tire Size Box

325/60R18 vs 325/70R18

325/70R18 compared with 325/60R18

+7.7% diameter, 0.0" width

325/70R18 is 35.91" 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 325/70R18 (dashed outline), drawn to scale

With 325/70R18 tires, when your speedometer says 60 mph you are really going

64.6 mph

325/70R18 is +2.56 inches (+7.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

325/60R18325/70R18Difference%
Overall diameter33.35"35.91"+2.56"+7.7%
Section width12.80"12.80"0.00"0.0%
Sidewall height7.68"8.96"+1.28"+16.7%
Circumference104.79"112.83"+8.04"+7.7%
Revolutions per mile604.7561.6−43.1−7.1%

Speedometer difference

If your vehicle came with 325/60R18 and you fit 325/70R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.5 mph+1.5 mph
30 mph32.3 mph+2.3 mph
40 mph43.1 mph+3.1 mph
50 mph53.8 mph+3.8 mph
60 mph64.6 mph+4.6 mph
65 mph70.0 mph+5.0 mph
70 mph75.4 mph+5.4 mph
75 mph80.8 mph+5.8 mph
80 mph86.1 mph+6.1 mph

Each size on its own

Questions

Which is bigger, 325/60R18 or 325/70R18?
325/70R18 is taller by 2.56 inches (35.91" vs 33.35"). 325/60R18 is the same width.
Can I replace 325/60R18 with 325/70R18?
It is not recommended without checking carefully. The diameter difference is +7.7%, 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 325/70R18 change my speedometer?
When your speedometer reads 60 mph with 325/70R18 fitted (calibrated for 325/60R18), your real speed is 64.6 mph. Your odometer will under-count miles by about 7.7%.
Will 325/70R18 lift my vehicle?
Ride height changes by half the diameter difference: +1.28 inches of ground clearance at the axle.

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