Tire Size Box

325/30R21 vs 325/35R21

325/35R21 compared with 325/30R21

+4.5% diameter, 0.0" width

325/35R21 is 29.96" tall vs 28.68". More than the 3% rule of thumb, so check carefully before switching.

28.7"21" rim3.8"12.8" wide
325/30R21 (solid) compared with 325/35R21 (dashed outline), drawn to scale

With 325/35R21 tires, when your speedometer says 60 mph you are really going

62.7 mph

325/35R21 is +1.28 inches (+4.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

325/30R21325/35R21Difference%
Overall diameter28.68"29.96"+1.28"+4.5%
Section width12.80"12.80"0.00"0.0%
Sidewall height3.84"4.48"+0.64"+16.7%
Circumference90.09"94.11"+4.02"+4.5%
Revolutions per mile703.3673.2−30.0−4.3%

Speedometer difference

If your vehicle came with 325/30R21 and you fit 325/35R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.3 mph+1.3 mph
40 mph41.8 mph+1.8 mph
50 mph52.2 mph+2.2 mph
60 mph62.7 mph+2.7 mph
65 mph67.9 mph+2.9 mph
70 mph73.1 mph+3.1 mph
75 mph78.3 mph+3.3 mph
80 mph83.6 mph+3.6 mph

Each size on its own

Questions

Which is bigger, 325/30R21 or 325/35R21?
325/35R21 is taller by 1.28 inches (29.96" vs 28.68"). 325/30R21 is the same width.
Can I replace 325/30R21 with 325/35R21?
It is not recommended without checking carefully. The diameter difference is +4.5%, 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 325/35R21 change my speedometer?
When your speedometer reads 60 mph with 325/35R21 fitted (calibrated for 325/30R21), your real speed is 62.7 mph. Your odometer will under-count miles by about 4.5%.
Will 325/35R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.64 inches of ground clearance at the axle.

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