Tire Size Box

185/75R15 vs 185/85R15

185/85R15 compared with 185/75R15

+5.6% diameter, 0.0" width

185/85R15 is 27.38" tall vs 25.93". More than the 3% rule of thumb, so check carefully before switching.

25.9"15" rim5.5"7.3" wide
185/75R15 (solid) compared with 185/85R15 (dashed outline), drawn to scale

With 185/85R15 tires, when your speedometer says 60 mph you are really going

63.4 mph

185/85R15 is +1.46 inches (+5.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

185/75R15185/85R15Difference%
Overall diameter25.93"27.38"+1.46"+5.6%
Section width7.28"7.28"0.00"0.0%
Sidewall height5.46"6.19"+0.73"+13.3%
Circumference81.45"86.02"+4.58"+5.6%
Revolutions per mile777.9736.5−41.4−5.3%

Speedometer difference

If your vehicle came with 185/75R15 and you fit 185/85R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.1 mph+1.1 mph
30 mph31.7 mph+1.7 mph
40 mph42.2 mph+2.2 mph
50 mph52.8 mph+2.8 mph
60 mph63.4 mph+3.4 mph
65 mph68.7 mph+3.7 mph
70 mph73.9 mph+3.9 mph
75 mph79.2 mph+4.2 mph
80 mph84.5 mph+4.5 mph

Each size on its own

Questions

Which is bigger, 185/75R15 or 185/85R15?
185/85R15 is taller by 1.46 inches (27.38" vs 25.93"). 185/75R15 is the same width.
Can I replace 185/75R15 with 185/85R15?
It is not recommended without checking carefully. The diameter difference is +5.6%, 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 185/85R15 change my speedometer?
When your speedometer reads 60 mph with 185/85R15 fitted (calibrated for 185/75R15), your real speed is 63.4 mph. Your odometer will under-count miles by about 5.6%.
Will 185/85R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.73 inches of ground clearance at the axle.

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