Tire Size Box

335/35R21 vs 325/40R21

325/40R21 compared with 335/35R21

+3.3% diameter, −0.4" width

325/40R21 is 31.24" tall vs 30.23". More than the 3% rule of thumb, so check carefully before switching.

30.2"21" rim4.6"13.2" wide
335/35R21 (solid) compared with 325/40R21 (dashed outline), drawn to scale

With 325/40R21 tires, when your speedometer says 60 mph you are really going

62.0 mph

325/40R21 is +1.00 inches (+3.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

335/35R21325/40R21Difference%
Overall diameter30.23"31.24"+1.00"+3.3%
Section width13.19"12.80"−0.39"−3.0%
Sidewall height4.62"5.12"+0.50"+10.9%
Circumference94.98"98.13"+3.15"+3.3%
Revolutions per mile667.1645.7−21.4−3.2%

Speedometer difference

If your vehicle came with 335/35R21 and you fit 325/40R21, 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 mph41.3 mph+1.3 mph
50 mph51.7 mph+1.7 mph
60 mph62.0 mph+2.0 mph
65 mph67.2 mph+2.2 mph
70 mph72.3 mph+2.3 mph
75 mph77.5 mph+2.5 mph
80 mph82.7 mph+2.7 mph

Each size on its own

Questions

Which is bigger, 335/35R21 or 325/40R21?
325/40R21 is taller by 1.00 inches (31.24" vs 30.23"). 335/35R21 is wider by 0.39 inches.
Can I replace 335/35R21 with 325/40R21?
It is not recommended without checking carefully. The diameter difference is +3.3%, 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 325/40R21 change my speedometer?
When your speedometer reads 60 mph with 325/40R21 fitted (calibrated for 335/35R21), your real speed is 62.0 mph. Your odometer will under-count miles by about 3.3%.
Will 325/40R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.50 inches of ground clearance at the axle.

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