Tire Size Box

355/25R21 vs 335/30R21

335/30R21 compared with 355/25R21

+3.3% diameter, −0.8" width

335/30R21 is 28.91" tall vs 27.99". More than the 3% rule of thumb, so check carefully before switching.

28.0"21" rim3.5"14.0" wide
355/25R21 (solid) compared with 335/30R21 (dashed outline), drawn to scale

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

62.0 mph

335/30R21 is +0.93 inches (+3.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

355/25R21335/30R21Difference%
Overall diameter27.99"28.91"+0.93"+3.3%
Section width13.98"13.19"−0.79"−5.6%
Sidewall height3.49"3.96"+0.46"+13.2%
Circumference87.93"90.83"+2.91"+3.3%
Revolutions per mile720.6697.5−23.1−3.2%

Speedometer difference

If your vehicle came with 355/25R21 and you fit 335/30R21, 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 mph67.1 mph+2.1 mph
70 mph72.3 mph+2.3 mph
75 mph77.5 mph+2.5 mph
80 mph82.6 mph+2.6 mph

Each size on its own

Questions

Which is bigger, 355/25R21 or 335/30R21?
335/30R21 is taller by 0.93 inches (28.91" vs 27.99"). 355/25R21 is wider by 0.79 inches.
Can I replace 355/25R21 with 335/30R21?
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 335/30R21 change my speedometer?
When your speedometer reads 60 mph with 335/30R21 fitted (calibrated for 355/25R21), your real speed is 62.0 mph. Your odometer will under-count miles by about 3.3%.
Will 335/30R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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