Tire Size Box

245/60R20 vs 335/40R21

335/40R21 compared with 245/60R20

−0.1% diameter, +3.5" width

335/40R21 is 31.55" tall vs 31.57". Within the 3% rule, so usually interchangeable.

31.6"20" rim5.8"9.6" wide
245/60R20 (solid) compared with 335/40R21 (dashed outline), drawn to scale

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

60.0 mph

335/40R21 is −0.02 inches (−0.1%) in overall diameter. That is within the 3% most shops and makers allow.

245/60R20335/40R21Difference%
Overall diameter31.57"31.55"−0.02"−0.1%
Section width9.65"13.19"+3.54"+36.7%
Sidewall height5.79"5.28"−0.51"−8.8%
Circumference99.20"99.12"−0.07"−0.1%
Revolutions per mile638.7639.2+0.5+0.1%

Speedometer difference

If your vehicle came with 245/60R20 and you fit 335/40R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.0 mph0.0 mph
30 mph30.0 mph0.0 mph
40 mph40.0 mph0.0 mph
50 mph50.0 mph0.0 mph
60 mph60.0 mph0.0 mph
65 mph65.0 mph0.0 mph
70 mph69.9 mph−0.1 mph
75 mph74.9 mph−0.1 mph
80 mph79.9 mph−0.1 mph

Each size on its own

Questions

Which is bigger, 245/60R20 or 335/40R21?
245/60R20 is taller by 0.02 inches (31.57" vs 31.55"). 335/40R21 is wider by 3.54 inches.
Can I replace 245/60R20 with 335/40R21?
Usually, yes. The diameter difference is −0.1%, inside the 3% rule of thumb most tire shops use. Check that the wider or taller tire clears your suspension and fenders, and that its load index meets your placard.
How much will 335/40R21 change my speedometer?
When your speedometer reads 60 mph with 335/40R21 fitted (calibrated for 245/60R20), your real speed is 60.0 mph. Your odometer will over-count miles by about 0.1%.
Will 335/40R21 lift my vehicle?
Ride height changes by half the diameter difference: −0.01 inches of ground clearance at the axle.

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