Tire Size Box

165/85R15 vs 185/85R15

185/85R15 compared with 165/85R15

+5.1% diameter, +0.8" width

185/85R15 is 27.38" tall vs 26.04". More than the 3% rule of thumb, so check carefully before switching.

26.0"15" rim5.5"6.5" wide
165/85R15 (solid) compared with 185/85R15 (dashed outline), drawn to scale

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

63.1 mph

185/85R15 is +1.34 inches (+5.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

165/85R15185/85R15Difference%
Overall diameter26.04"27.38"+1.34"+5.1%
Section width6.50"7.28"+0.79"+12.1%
Sidewall height5.52"6.19"+0.67"+12.1%
Circumference81.82"86.02"+4.21"+5.1%
Revolutions per mile774.4736.5−37.9−4.9%

Speedometer difference

If your vehicle came with 165/85R15 and you fit 185/85R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.0 mph+1.0 mph
30 mph31.5 mph+1.5 mph
40 mph42.1 mph+2.1 mph
50 mph52.6 mph+2.6 mph
60 mph63.1 mph+3.1 mph
65 mph68.3 mph+3.3 mph
70 mph73.6 mph+3.6 mph
75 mph78.9 mph+3.9 mph
80 mph84.1 mph+4.1 mph

Each size on its own

Questions

Which is bigger, 165/85R15 or 185/85R15?
185/85R15 is taller by 1.34 inches (27.38" vs 26.04"). 185/85R15 is wider by 0.79 inches.
Can I replace 165/85R15 with 185/85R15?
It is not recommended without checking carefully. The diameter difference is +5.1%, 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 185/85R15 change my speedometer?
When your speedometer reads 60 mph with 185/85R15 fitted (calibrated for 165/85R15), your real speed is 63.1 mph. Your odometer will under-count miles by about 5.1%.
Will 185/85R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.67 inches of ground clearance at the axle.

Other comparisons