Tire Size Box

335/25R21 vs 335/30R21

335/30R21 compared with 335/25R21

+4.8% diameter, 0.0" width

335/30R21 is 28.91" 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 335/30R21 (dashed outline), drawn to scale

With 335/30R21 tires, when your speedometer says 60 mph you are really going

62.9 mph

335/30R21 is +1.32 inches (+4.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

335/25R21335/30R21Difference%
Overall diameter27.59"28.91"+1.32"+4.8%
Section width13.19"13.19"0.00"0.0%
Sidewall height3.30"3.96"+0.66"+20.0%
Circumference86.69"90.83"+4.14"+4.8%
Revolutions per mile730.9697.5−33.3−4.6%

Speedometer difference

If your vehicle came with 335/25R21 and you fit 335/30R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.0 mph+1.0 mph
30 mph31.4 mph+1.4 mph
40 mph41.9 mph+1.9 mph
50 mph52.4 mph+2.4 mph
60 mph62.9 mph+2.9 mph
65 mph68.1 mph+3.1 mph
70 mph73.3 mph+3.3 mph
75 mph78.6 mph+3.6 mph
80 mph83.8 mph+3.8 mph

Each size on its own

Questions

Which is bigger, 335/25R21 or 335/30R21?
335/30R21 is taller by 1.32 inches (28.91" vs 27.59"). 335/25R21 is the same width.
Can I replace 335/25R21 with 335/30R21?
It is not recommended without checking carefully. The diameter difference is +4.8%, 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 335/30R21 change my speedometer?
When your speedometer reads 60 mph with 335/30R21 fitted (calibrated for 335/25R21), your real speed is 62.9 mph. Your odometer will under-count miles by about 4.8%.
Will 335/30R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.66 inches of ground clearance at the axle.

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