Tire Size Box

335/40R21 vs 325/45R21

325/45R21 compared with 335/40R21

+3.1% diameter, −0.4" width

325/45R21 is 32.52" tall vs 31.55". More than the 3% rule of thumb, so check carefully before switching.

31.6"21" rim5.3"13.2" wide
335/40R21 (solid) compared with 325/45R21 (dashed outline), drawn to scale

With 325/45R21 tires, when your speedometer says 60 mph you are really going

61.8 mph

325/45R21 is +0.96 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

335/40R21325/45R21Difference%
Overall diameter31.55"32.52"+0.96"+3.1%
Section width13.19"12.80"−0.39"−3.0%
Sidewall height5.28"5.76"+0.48"+9.1%
Circumference99.12"102.15"+3.03"+3.1%
Revolutions per mile639.2620.3−19.0−3.0%

Speedometer difference

If your vehicle came with 335/40R21 and you fit 325/45R21, 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 mph41.2 mph+1.2 mph
50 mph51.5 mph+1.5 mph
60 mph61.8 mph+1.8 mph
65 mph67.0 mph+2.0 mph
70 mph72.1 mph+2.1 mph
75 mph77.3 mph+2.3 mph
80 mph82.4 mph+2.4 mph

Each size on its own

Questions

Which is bigger, 335/40R21 or 325/45R21?
325/45R21 is taller by 0.96 inches (32.52" vs 31.55"). 335/40R21 is wider by 0.39 inches.
Can I replace 335/40R21 with 325/45R21?
It is not recommended without checking carefully. The diameter difference is +3.1%, 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 325/45R21 change my speedometer?
When your speedometer reads 60 mph with 325/45R21 fitted (calibrated for 335/40R21), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.1%.
Will 325/45R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.48 inches of ground clearance at the axle.

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