Tire Size Box

275/35R20 vs 275/40R20

275/40R20 compared with 275/35R20

+3.9% diameter, 0.0" width

275/40R20 is 28.66" tall vs 27.58". More than the 3% rule of thumb, so check carefully before switching.

27.6"20" rim3.8"10.8" wide
275/35R20 (solid) compared with 275/40R20 (dashed outline), drawn to scale

With 275/40R20 tires, when your speedometer says 60 mph you are really going

62.4 mph

275/40R20 is +1.08 inches (+3.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

275/35R20275/40R20Difference%
Overall diameter27.58"28.66"+1.08"+3.9%
Section width10.83"10.83"0.00"0.0%
Sidewall height3.79"4.33"+0.54"+14.3%
Circumference86.64"90.04"+3.40"+3.9%
Revolutions per mile731.3703.7−27.6−3.8%

Speedometer difference

If your vehicle came with 275/35R20 and you fit 275/40R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.6 mph+1.6 mph
50 mph52.0 mph+2.0 mph
60 mph62.4 mph+2.4 mph
65 mph67.6 mph+2.6 mph
70 mph72.7 mph+2.7 mph
75 mph77.9 mph+2.9 mph
80 mph83.1 mph+3.1 mph

Each size on its own

Questions

Which is bigger, 275/35R20 or 275/40R20?
275/40R20 is taller by 1.08 inches (28.66" vs 27.58"). 275/35R20 is the same width.
Can I replace 275/35R20 with 275/40R20?
It is not recommended without checking carefully. The diameter difference is +3.9%, 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 275/40R20 change my speedometer?
When your speedometer reads 60 mph with 275/40R20 fitted (calibrated for 275/35R20), your real speed is 62.4 mph. Your odometer will under-count miles by about 3.9%.
Will 275/40R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.54 inches of ground clearance at the axle.

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