Tire Size Box

345/40R21 vs 335/45R21

335/45R21 compared with 345/40R21

+3.2% diameter, −0.4" width

335/45R21 is 32.87" tall vs 31.87". More than the 3% rule of thumb, so check carefully before switching.

31.9"21" rim5.4"13.6" wide
345/40R21 (solid) compared with 335/45R21 (dashed outline), drawn to scale

With 335/45R21 tires, when your speedometer says 60 mph you are really going

61.9 mph

335/45R21 is +1.00 inches (+3.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

345/40R21335/45R21Difference%
Overall diameter31.87"32.87"+1.00"+3.2%
Section width13.58"13.19"−0.39"−2.9%
Sidewall height5.43"5.94"+0.50"+9.2%
Circumference100.11"103.26"+3.15"+3.2%
Revolutions per mile632.9613.6−19.3−3.1%

Speedometer difference

If your vehicle came with 345/40R21 and you fit 335/45R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph30.9 mph+0.9 mph
40 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.0 mph+2.0 mph
70 mph72.2 mph+2.2 mph
75 mph77.4 mph+2.4 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 345/40R21 or 335/45R21?
335/45R21 is taller by 1.00 inches (32.87" vs 31.87"). 345/40R21 is wider by 0.39 inches.
Can I replace 345/40R21 with 335/45R21?
It is not recommended without checking carefully. The diameter difference is +3.2%, 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 335/45R21 change my speedometer?
When your speedometer reads 60 mph with 335/45R21 fitted (calibrated for 345/40R21), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.2%.
Will 335/45R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.50 inches of ground clearance at the axle.

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