Tire Size Box

235/35R17 vs 235/40R17

235/40R17 compared with 235/35R17

+3.9% diameter, 0.0" width

235/40R17 is 24.40" tall vs 23.48". More than the 3% rule of thumb, so check carefully before switching.

23.5"17" rim3.2"9.3" wide
235/35R17 (solid) compared with 235/40R17 (dashed outline), drawn to scale

With 235/40R17 tires, when your speedometer says 60 mph you are really going

62.4 mph

235/40R17 is +0.93 inches (+3.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/35R17235/40R17Difference%
Overall diameter23.48"24.40"+0.93"+3.9%
Section width9.25"9.25"0.00"0.0%
Sidewall height3.24"3.70"+0.46"+14.3%
Circumference73.75"76.66"+2.91"+3.9%
Revolutions per mile859.1826.5−32.6−3.8%

Speedometer difference

If your vehicle came with 235/35R17 and you fit 235/40R17, 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 mph72.8 mph+2.8 mph
75 mph78.0 mph+3.0 mph
80 mph83.2 mph+3.2 mph

Each size on its own

Questions

Which is bigger, 235/35R17 or 235/40R17?
235/40R17 is taller by 0.93 inches (24.40" vs 23.48"). 235/35R17 is the same width.
Can I replace 235/35R17 with 235/40R17?
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 235/40R17 change my speedometer?
When your speedometer reads 60 mph with 235/40R17 fitted (calibrated for 235/35R17), your real speed is 62.4 mph. Your odometer will under-count miles by about 3.9%.
Will 235/40R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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