Tire Size Box

335/40R18 vs 325/45R18

325/45R18 compared with 335/40R18

+3.4% diameter, −0.4" width

325/45R18 is 29.52" tall vs 28.55". More than the 3% rule of thumb, so check carefully before switching.

28.6"18" rim5.3"13.2" wide
335/40R18 (solid) compared with 325/45R18 (dashed outline), drawn to scale

With 325/45R18 tires, when your speedometer says 60 mph you are really going

62.0 mph

325/45R18 is +0.96 inches (+3.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

335/40R18325/45R18Difference%
Overall diameter28.55"29.52"+0.96"+3.4%
Section width13.19"12.80"−0.39"−3.0%
Sidewall height5.28"5.76"+0.48"+9.1%
Circumference89.70"92.73"+3.03"+3.4%
Revolutions per mile706.4683.3−23.1−3.3%

Speedometer difference

If your vehicle came with 335/40R18 and you fit 325/45R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.4 mph+1.4 mph
50 mph51.7 mph+1.7 mph
60 mph62.0 mph+2.0 mph
65 mph67.2 mph+2.2 mph
70 mph72.4 mph+2.4 mph
75 mph77.5 mph+2.5 mph
80 mph82.7 mph+2.7 mph

Each size on its own

Questions

Which is bigger, 335/40R18 or 325/45R18?
325/45R18 is taller by 0.96 inches (29.52" vs 28.55"). 335/40R18 is wider by 0.39 inches.
Can I replace 335/40R18 with 325/45R18?
It is not recommended without checking carefully. The diameter difference is +3.4%, 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 325/45R18 change my speedometer?
When your speedometer reads 60 mph with 325/45R18 fitted (calibrated for 335/40R18), your real speed is 62.0 mph. Your odometer will under-count miles by about 3.4%.
Will 325/45R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.48 inches of ground clearance at the axle.

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