Tire Size Box

345/25R21 vs 335/30R21

335/30R21 compared with 345/25R21

+4.0% diameter, −0.4" width

335/30R21 is 28.91" tall vs 27.79". More than the 3% rule of thumb, so check carefully before switching.

27.8"21" rim3.4"13.6" wide
345/25R21 (solid) compared with 335/30R21 (dashed outline), drawn to scale

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

62.4 mph

335/30R21 is +1.12 inches (+4.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

345/25R21335/30R21Difference%
Overall diameter27.79"28.91"+1.12"+4.0%
Section width13.58"13.19"−0.39"−2.9%
Sidewall height3.40"3.96"+0.56"+16.5%
Circumference87.31"90.83"+3.53"+4.0%
Revolutions per mile725.7697.5−28.2−3.9%

Speedometer difference

If your vehicle came with 345/25R21 and you fit 335/30R21, 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 mph72.8 mph+2.8 mph
75 mph78.0 mph+3.0 mph
80 mph83.2 mph+3.2 mph

Each size on its own

Questions

Which is bigger, 345/25R21 or 335/30R21?
335/30R21 is taller by 1.12 inches (28.91" vs 27.79"). 345/25R21 is wider by 0.39 inches.
Can I replace 345/25R21 with 335/30R21?
It is not recommended without checking carefully. The diameter difference is +4.0%, 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 345/25R21), your real speed is 62.4 mph. Your odometer will under-count miles by about 4.0%.
Will 335/30R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.56 inches of ground clearance at the axle.

Other comparisons