Tire Size Box

285/35R17 vs 285/40R17

285/40R17 compared with 285/35R17

+4.5% diameter, 0.0" width

285/40R17 is 25.98" tall vs 24.85". More than the 3% rule of thumb, so check carefully before switching.

24.9"17" rim3.9"11.2" wide
285/35R17 (solid) compared with 285/40R17 (dashed outline), drawn to scale

With 285/40R17 tires, when your speedometer says 60 mph you are really going

62.7 mph

285/40R17 is +1.12 inches (+4.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/35R17285/40R17Difference%
Overall diameter24.85"25.98"+1.12"+4.5%
Section width11.22"11.22"0.00"0.0%
Sidewall height3.93"4.49"+0.56"+14.3%
Circumference78.08"81.61"+3.53"+4.5%
Revolutions per mile811.5776.4−35.1−4.3%

Speedometer difference

If your vehicle came with 285/35R17 and you fit 285/40R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.4 mph+1.4 mph
40 mph41.8 mph+1.8 mph
50 mph52.3 mph+2.3 mph
60 mph62.7 mph+2.7 mph
65 mph67.9 mph+2.9 mph
70 mph73.2 mph+3.2 mph
75 mph78.4 mph+3.4 mph
80 mph83.6 mph+3.6 mph

Each size on its own

Questions

Which is bigger, 285/35R17 or 285/40R17?
285/40R17 is taller by 1.12 inches (25.98" vs 24.85"). 285/35R17 is the same width.
Can I replace 285/35R17 with 285/40R17?
It is not recommended without checking carefully. The diameter difference is +4.5%, 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 285/40R17 change my speedometer?
When your speedometer reads 60 mph with 285/40R17 fitted (calibrated for 285/35R17), your real speed is 62.7 mph. Your odometer will under-count miles by about 4.5%.
Will 285/40R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.56 inches of ground clearance at the axle.

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