Tire Size Box

335/35R18 vs 335/40R18

335/40R18 compared with 335/35R18

+4.8% diameter, 0.0" width

335/40R18 is 28.55" tall vs 27.23". More than the 3% rule of thumb, so check carefully before switching.

27.2"18" rim4.6"13.2" wide
335/35R18 (solid) compared with 335/40R18 (dashed outline), drawn to scale

With 335/40R18 tires, when your speedometer says 60 mph you are really going

62.9 mph

335/40R18 is +1.32 inches (+4.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

335/35R18335/40R18Difference%
Overall diameter27.23"28.55"+1.32"+4.8%
Section width13.19"13.19"0.00"0.0%
Sidewall height4.62"5.28"+0.66"+14.3%
Circumference85.55"89.70"+4.14"+4.8%
Revolutions per mile740.6706.4−34.2−4.6%

Speedometer difference

If your vehicle came with 335/35R18 and you fit 335/40R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.0 mph+1.0 mph
30 mph31.5 mph+1.5 mph
40 mph41.9 mph+1.9 mph
50 mph52.4 mph+2.4 mph
60 mph62.9 mph+2.9 mph
65 mph68.1 mph+3.1 mph
70 mph73.4 mph+3.4 mph
75 mph78.6 mph+3.6 mph
80 mph83.9 mph+3.9 mph

Each size on its own

Questions

Which is bigger, 335/35R18 or 335/40R18?
335/40R18 is taller by 1.32 inches (28.55" vs 27.23"). 335/35R18 is the same width.
Can I replace 335/35R18 with 335/40R18?
It is not recommended without checking carefully. The diameter difference is +4.8%, 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 335/40R18 change my speedometer?
When your speedometer reads 60 mph with 335/40R18 fitted (calibrated for 335/35R18), your real speed is 62.9 mph. Your odometer will under-count miles by about 4.8%.
Will 335/40R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.66 inches of ground clearance at the axle.

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