Tire Size Box

245/35R17 vs 245/40R17

245/40R17 compared with 245/35R17

+4.1% diameter, 0.0" width

245/40R17 is 24.72" tall vs 23.75". More than the 3% rule of thumb, so check carefully before switching.

23.8"17" rim3.4"9.6" wide
245/35R17 (solid) compared with 245/40R17 (dashed outline), drawn to scale

With 245/40R17 tires, when your speedometer says 60 mph you are really going

62.4 mph

245/40R17 is +0.96 inches (+4.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/35R17245/40R17Difference%
Overall diameter23.75"24.72"+0.96"+4.1%
Section width9.65"9.65"0.00"0.0%
Sidewall height3.38"3.86"+0.48"+14.3%
Circumference74.62"77.65"+3.03"+4.1%
Revolutions per mile849.1816.0−33.1−3.9%

Speedometer difference

If your vehicle came with 245/35R17 and you fit 245/40R17, 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, 245/35R17 or 245/40R17?
245/40R17 is taller by 0.96 inches (24.72" vs 23.75"). 245/35R17 is the same width.
Can I replace 245/35R17 with 245/40R17?
It is not recommended without checking carefully. The diameter difference is +4.1%, 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 245/40R17 change my speedometer?
When your speedometer reads 60 mph with 245/40R17 fitted (calibrated for 245/35R17), your real speed is 62.4 mph. Your odometer will under-count miles by about 4.1%.
Will 245/40R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.48 inches of ground clearance at the axle.

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