Tire Size Box

285/80R15 vs 285/85R15

285/85R15 compared with 285/80R15

+3.4% diameter, 0.0" width

285/85R15 is 34.07" tall vs 32.95". More than the 3% rule of thumb, so check carefully before switching.

33.0"15" rim9.0"11.2" wide
285/80R15 (solid) compared with 285/85R15 (dashed outline), drawn to scale

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

62.0 mph

285/85R15 is +1.12 inches (+3.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/80R15285/85R15Difference%
Overall diameter32.95"34.07"+1.12"+3.4%
Section width11.22"11.22"0.00"0.0%
Sidewall height8.98"9.54"+0.56"+6.3%
Circumference103.52"107.05"+3.53"+3.4%
Revolutions per mile612.0591.9−20.2−3.3%

Speedometer difference

If your vehicle came with 285/80R15 and you fit 285/85R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.4 mph+1.4 mph
50 mph51.7 mph+1.7 mph
60 mph62.0 mph+2.0 mph
65 mph67.2 mph+2.2 mph
70 mph72.4 mph+2.4 mph
75 mph77.6 mph+2.6 mph
80 mph82.7 mph+2.7 mph

Each size on its own

Questions

Which is bigger, 285/80R15 or 285/85R15?
285/85R15 is taller by 1.12 inches (34.07" vs 32.95"). 285/80R15 is the same width.
Can I replace 285/80R15 with 285/85R15?
It is not recommended without checking carefully. The diameter difference is +3.4%, 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 285/80R15), your real speed is 62.0 mph. Your odometer will under-count miles by about 3.4%.
Will 285/85R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.56 inches of ground clearance at the axle.

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