Tire Size Box

285/75R15 vs 285/85R15

285/85R15 compared with 285/75R15

+7.1% diameter, 0.0" width

285/85R15 is 34.07" tall vs 31.83". More than the 3% rule of thumb, so check carefully before switching.

31.8"15" rim8.4"11.2" wide
285/75R15 (solid) compared with 285/85R15 (dashed outline), drawn to scale

With 285/85R15 tires, when your speedometer says 60 mph you are really going

64.2 mph

285/85R15 is +2.24 inches (+7.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/75R15285/85R15Difference%
Overall diameter31.83"34.07"+2.24"+7.1%
Section width11.22"11.22"0.00"0.0%
Sidewall height8.42"9.54"+1.12"+13.3%
Circumference100.00"107.05"+7.05"+7.1%
Revolutions per mile633.6591.9−41.7−6.6%

Speedometer difference

If your vehicle came with 285/75R15 and you fit 285/85R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.4 mph+1.4 mph
30 mph32.1 mph+2.1 mph
40 mph42.8 mph+2.8 mph
50 mph53.5 mph+3.5 mph
60 mph64.2 mph+4.2 mph
65 mph69.6 mph+4.6 mph
70 mph74.9 mph+4.9 mph
75 mph80.3 mph+5.3 mph
80 mph85.6 mph+5.6 mph

Each size on its own

Questions

Which is bigger, 285/75R15 or 285/85R15?
285/85R15 is taller by 2.24 inches (34.07" vs 31.83"). 285/75R15 is the same width.
Can I replace 285/75R15 with 285/85R15?
It is not recommended without checking carefully. The diameter difference is +7.1%, 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 285/85R15 change my speedometer?
When your speedometer reads 60 mph with 285/85R15 fitted (calibrated for 285/75R15), your real speed is 64.2 mph. Your odometer will under-count miles by about 7.1%.
Will 285/85R15 lift my vehicle?
Ride height changes by half the diameter difference: +1.12 inches of ground clearance at the axle.

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