Tire Size Box

335/30R20 vs 335/40R20

335/40R20 compared with 335/30R20

+9.4% diameter, 0.0" width

335/40R20 is 30.55" tall vs 27.91". More than the 3% rule of thumb, so check carefully before switching.

27.9"20" rim4.0"13.2" wide
335/30R20 (solid) compared with 335/40R20 (dashed outline), drawn to scale

With 335/40R20 tires, when your speedometer says 60 mph you are really going

65.7 mph

335/40R20 is +2.64 inches (+9.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

335/30R20335/40R20Difference%
Overall diameter27.91"30.55"+2.64"+9.4%
Section width13.19"13.19"0.00"0.0%
Sidewall height3.96"5.28"+1.32"+33.3%
Circumference87.69"95.98"+8.29"+9.4%
Revolutions per mile722.5660.1−62.4−8.6%

Speedometer difference

If your vehicle came with 335/30R20 and you fit 335/40R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.9 mph+1.9 mph
30 mph32.8 mph+2.8 mph
40 mph43.8 mph+3.8 mph
50 mph54.7 mph+4.7 mph
60 mph65.7 mph+5.7 mph
65 mph71.1 mph+6.1 mph
70 mph76.6 mph+6.6 mph
75 mph82.1 mph+7.1 mph
80 mph87.6 mph+7.6 mph

Each size on its own

Questions

Which is bigger, 335/30R20 or 335/40R20?
335/40R20 is taller by 2.64 inches (30.55" vs 27.91"). 335/30R20 is the same width.
Can I replace 335/30R20 with 335/40R20?
It is not recommended without checking carefully. The diameter difference is +9.4%, 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 335/40R20 change my speedometer?
When your speedometer reads 60 mph with 335/40R20 fitted (calibrated for 335/30R20), your real speed is 65.7 mph. Your odometer will under-count miles by about 9.4%.
Will 335/40R20 lift my vehicle?
Ride height changes by half the diameter difference: +1.32 inches of ground clearance at the axle.

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