Tire Size Box

345/35R21 vs 335/40R21

335/40R21 compared with 345/35R21

+3.4% diameter, −0.4" width

335/40R21 is 31.55" tall vs 30.51". More than the 3% rule of thumb, so check carefully before switching.

30.5"21" rim4.8"13.6" wide
345/35R21 (solid) compared with 335/40R21 (dashed outline), drawn to scale

With 335/40R21 tires, when your speedometer says 60 mph you are really going

62.1 mph

335/40R21 is +1.04 inches (+3.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

345/35R21335/40R21Difference%
Overall diameter30.51"31.55"+1.04"+3.4%
Section width13.58"13.19"−0.39"−2.9%
Sidewall height4.75"5.28"+0.52"+11.0%
Circumference95.84"99.12"+3.28"+3.4%
Revolutions per mile661.1639.2−21.9−3.3%

Speedometer difference

If your vehicle came with 345/35R21 and you fit 335/40R21, 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 mph41.4 mph+1.4 mph
50 mph51.7 mph+1.7 mph
60 mph62.1 mph+2.1 mph
65 mph67.2 mph+2.2 mph
70 mph72.4 mph+2.4 mph
75 mph77.6 mph+2.6 mph
80 mph82.7 mph+2.7 mph

Each size on its own

Questions

Which is bigger, 345/35R21 or 335/40R21?
335/40R21 is taller by 1.04 inches (31.55" vs 30.51"). 345/35R21 is wider by 0.39 inches.
Can I replace 345/35R21 with 335/40R21?
It is not recommended without checking carefully. The diameter difference is +3.4%, 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 335/40R21 change my speedometer?
When your speedometer reads 60 mph with 335/40R21 fitted (calibrated for 345/35R21), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.4%.
Will 335/40R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.52 inches of ground clearance at the axle.

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