Tire Size Box

335/40R20 vs 325/45R20

325/45R20 compared with 335/40R20

+3.2% diameter, −0.4" width

325/45R20 is 31.52" tall vs 30.55". More than the 3% rule of thumb, so check carefully before switching.

30.6"20" rim5.3"13.2" wide
335/40R20 (solid) compared with 325/45R20 (dashed outline), drawn to scale

With 325/45R20 tires, when your speedometer says 60 mph you are really going

61.9 mph

325/45R20 is +0.96 inches (+3.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

335/40R20325/45R20Difference%
Overall diameter30.55"31.52"+0.96"+3.2%
Section width13.19"12.80"−0.39"−3.0%
Sidewall height5.28"5.76"+0.48"+9.1%
Circumference95.98"99.01"+3.03"+3.2%
Revolutions per mile660.1639.9−20.2−3.1%

Speedometer difference

If your vehicle came with 335/40R20 and you fit 325/45R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph30.9 mph+0.9 mph
40 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.1 mph+2.1 mph
70 mph72.2 mph+2.2 mph
75 mph77.4 mph+2.4 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 335/40R20 or 325/45R20?
325/45R20 is taller by 0.96 inches (31.52" vs 30.55"). 335/40R20 is wider by 0.39 inches.
Can I replace 335/40R20 with 325/45R20?
It is not recommended without checking carefully. The diameter difference is +3.2%, 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 325/45R20 change my speedometer?
When your speedometer reads 60 mph with 325/45R20 fitted (calibrated for 335/40R20), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.2%.
Will 325/45R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.48 inches of ground clearance at the axle.

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