Tire Size Box

335/25R21 vs 325/30R21

325/30R21 compared with 335/25R21

+3.9% diameter, −0.4" width

325/30R21 is 28.68" tall vs 27.59". More than the 3% rule of thumb, so check carefully before switching.

27.6"21" rim3.3"13.2" wide
335/25R21 (solid) compared with 325/30R21 (dashed outline), drawn to scale

With 325/30R21 tires, when your speedometer says 60 mph you are really going

62.4 mph

325/30R21 is +1.08 inches (+3.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

335/25R21325/30R21Difference%
Overall diameter27.59"28.68"+1.08"+3.9%
Section width13.19"12.80"−0.39"−3.0%
Sidewall height3.30"3.84"+0.54"+16.4%
Circumference86.69"90.09"+3.40"+3.9%
Revolutions per mile730.9703.3−27.6−3.8%

Speedometer difference

If your vehicle came with 335/25R21 and you fit 325/30R21, 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 mph41.6 mph+1.6 mph
50 mph52.0 mph+2.0 mph
60 mph62.4 mph+2.4 mph
65 mph67.6 mph+2.6 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, 335/25R21 or 325/30R21?
325/30R21 is taller by 1.08 inches (28.68" vs 27.59"). 335/25R21 is wider by 0.39 inches.
Can I replace 335/25R21 with 325/30R21?
It is not recommended without checking carefully. The diameter difference is +3.9%, 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 325/30R21 change my speedometer?
When your speedometer reads 60 mph with 325/30R21 fitted (calibrated for 335/25R21), your real speed is 62.4 mph. Your odometer will under-count miles by about 3.9%.
Will 325/30R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.54 inches of ground clearance at the axle.

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