Tire Size Box

285/40R17 vs 285/45R17

285/45R17 compared with 285/40R17

+4.3% diameter, 0.0" width

285/45R17 is 27.10" tall vs 25.98". More than the 3% rule of thumb, so check carefully before switching.

26.0"17" rim4.5"11.2" wide
285/40R17 (solid) compared with 285/45R17 (dashed outline), drawn to scale

With 285/45R17 tires, when your speedometer says 60 mph you are really going

62.6 mph

285/45R17 is +1.12 inches (+4.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/40R17285/45R17Difference%
Overall diameter25.98"27.10"+1.12"+4.3%
Section width11.22"11.22"0.00"0.0%
Sidewall height4.49"5.05"+0.56"+12.5%
Circumference81.61"85.13"+3.53"+4.3%
Revolutions per mile776.4744.3−32.1−4.1%

Speedometer difference

If your vehicle came with 285/40R17 and you fit 285/45R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.3 mph+1.3 mph
40 mph41.7 mph+1.7 mph
50 mph52.2 mph+2.2 mph
60 mph62.6 mph+2.6 mph
65 mph67.8 mph+2.8 mph
70 mph73.0 mph+3.0 mph
75 mph78.2 mph+3.2 mph
80 mph83.5 mph+3.5 mph

Each size on its own

Questions

Which is bigger, 285/40R17 or 285/45R17?
285/45R17 is taller by 1.12 inches (27.10" vs 25.98"). 285/40R17 is the same width.
Can I replace 285/40R17 with 285/45R17?
It is not recommended without checking carefully. The diameter difference is +4.3%, 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 285/45R17 change my speedometer?
When your speedometer reads 60 mph with 285/45R17 fitted (calibrated for 285/40R17), your real speed is 62.6 mph. Your odometer will under-count miles by about 4.3%.
Will 285/45R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.56 inches of ground clearance at the axle.

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