Tire Size Box

165/65R15 vs 185/65R15

185/65R15 compared with 165/65R15

+4.4% diameter, +0.8" width

185/65R15 is 24.47" tall vs 23.44". More than the 3% rule of thumb, so check carefully before switching.

23.4"15" rim4.2"6.5" wide
165/65R15 (solid) compared with 185/65R15 (dashed outline), drawn to scale

With 185/65R15 tires, when your speedometer says 60 mph you are really going

62.6 mph

185/65R15 is +1.02 inches (+4.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

165/65R15185/65R15Difference%
Overall diameter23.44"24.47"+1.02"+4.4%
Section width6.50"7.28"+0.79"+12.1%
Sidewall height4.22"4.73"+0.51"+12.1%
Circumference73.65"76.87"+3.22"+4.4%
Revolutions per mile860.2824.2−36.0−4.2%

Speedometer difference

If your vehicle came with 165/65R15 and you fit 185/65R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.3 mph+1.3 mph
40 mph41.7 mph+1.7 mph
50 mph52.2 mph+2.2 mph
60 mph62.6 mph+2.6 mph
65 mph67.8 mph+2.8 mph
70 mph73.1 mph+3.1 mph
75 mph78.3 mph+3.3 mph
80 mph83.5 mph+3.5 mph

Each size on its own

Questions

Which is bigger, 165/65R15 or 185/65R15?
185/65R15 is taller by 1.02 inches (24.47" vs 23.44"). 185/65R15 is wider by 0.79 inches.
Can I replace 165/65R15 with 185/65R15?
It is not recommended without checking carefully. The diameter difference is +4.4%, 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 185/65R15 change my speedometer?
When your speedometer reads 60 mph with 185/65R15 fitted (calibrated for 165/65R15), your real speed is 62.6 mph. Your odometer will under-count miles by about 4.4%.
Will 185/65R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.51 inches of ground clearance at the axle.

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