Tire Size Box

335/35R21 vs 335/40R21

335/40R21 compared with 335/35R21

+4.4% diameter, 0.0" width

335/40R21 is 31.55" tall vs 30.23". More than the 3% rule of thumb, so check carefully before switching.

30.2"21" rim4.6"13.2" wide
335/35R21 (solid) compared with 335/40R21 (dashed outline), drawn to scale

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

62.6 mph

335/40R21 is +1.32 inches (+4.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

335/35R21335/40R21Difference%
Overall diameter30.23"31.55"+1.32"+4.4%
Section width13.19"13.19"0.00"0.0%
Sidewall height4.62"5.28"+0.66"+14.3%
Circumference94.98"99.12"+4.14"+4.4%
Revolutions per mile667.1639.2−27.9−4.2%

Speedometer difference

If your vehicle came with 335/35R21 and you fit 335/40R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.3 mph+1.3 mph
40 mph41.7 mph+1.7 mph
50 mph52.2 mph+2.2 mph
60 mph62.6 mph+2.6 mph
65 mph67.8 mph+2.8 mph
70 mph73.1 mph+3.1 mph
75 mph78.3 mph+3.3 mph
80 mph83.5 mph+3.5 mph

Each size on its own

Questions

Which is bigger, 335/35R21 or 335/40R21?
335/40R21 is taller by 1.32 inches (31.55" vs 30.23"). 335/35R21 is the same width.
Can I replace 335/35R21 with 335/40R21?
It is not recommended without checking carefully. The diameter difference is +4.4%, 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 335/35R21), your real speed is 62.6 mph. Your odometer will under-count miles by about 4.4%.
Will 335/40R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.66 inches of ground clearance at the axle.

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