Tire Size Box

165/75R15 vs 185/75R15

185/75R15 compared with 165/75R15

+4.8% diameter, +0.8" width

185/75R15 is 25.93" tall vs 24.74". More than the 3% rule of thumb, so check carefully before switching.

24.7"15" rim4.9"6.5" wide
165/75R15 (solid) compared with 185/75R15 (dashed outline), drawn to scale

With 185/75R15 tires, when your speedometer says 60 mph you are really going

62.9 mph

185/75R15 is +1.18 inches (+4.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

165/75R15185/75R15Difference%
Overall diameter24.74"25.93"+1.18"+4.8%
Section width6.50"7.28"+0.79"+12.1%
Sidewall height4.87"5.46"+0.59"+12.1%
Circumference77.74"81.45"+3.71"+4.8%
Revolutions per mile815.1777.9−37.1−4.6%

Speedometer difference

If your vehicle came with 165/75R15 and you fit 185/75R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.0 mph+1.0 mph
30 mph31.4 mph+1.4 mph
40 mph41.9 mph+1.9 mph
50 mph52.4 mph+2.4 mph
60 mph62.9 mph+2.9 mph
65 mph68.1 mph+3.1 mph
70 mph73.3 mph+3.3 mph
75 mph78.6 mph+3.6 mph
80 mph83.8 mph+3.8 mph

Each size on its own

Questions

Which is bigger, 165/75R15 or 185/75R15?
185/75R15 is taller by 1.18 inches (25.93" vs 24.74"). 185/75R15 is wider by 0.79 inches.
Can I replace 165/75R15 with 185/75R15?
It is not recommended without checking carefully. The diameter difference is +4.8%, 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 185/75R15 change my speedometer?
When your speedometer reads 60 mph with 185/75R15 fitted (calibrated for 165/75R15), your real speed is 62.9 mph. Your odometer will under-count miles by about 4.8%.
Will 185/75R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.59 inches of ground clearance at the axle.

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