Tire Size Box

165/70R15 vs 185/70R15

185/70R15 compared with 165/70R15

+4.6% diameter, +0.8" width

185/70R15 is 25.20" tall vs 24.09". More than the 3% rule of thumb, so check carefully before switching.

24.1"15" rim4.5"6.5" wide
165/70R15 (solid) compared with 185/70R15 (dashed outline), drawn to scale

With 185/70R15 tires, when your speedometer says 60 mph you are really going

62.7 mph

185/70R15 is +1.10 inches (+4.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

165/70R15185/70R15Difference%
Overall diameter24.09"25.20"+1.10"+4.6%
Section width6.50"7.28"+0.79"+12.1%
Sidewall height4.55"5.10"+0.55"+12.1%
Circumference75.70"79.16"+3.46"+4.6%
Revolutions per mile837.0800.4−36.6−4.4%

Speedometer difference

If your vehicle came with 165/70R15 and you fit 185/70R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.4 mph+1.4 mph
40 mph41.8 mph+1.8 mph
50 mph52.3 mph+2.3 mph
60 mph62.7 mph+2.7 mph
65 mph68.0 mph+3.0 mph
70 mph73.2 mph+3.2 mph
75 mph78.4 mph+3.4 mph
80 mph83.7 mph+3.7 mph

Each size on its own

Questions

Which is bigger, 165/70R15 or 185/70R15?
185/70R15 is taller by 1.10 inches (25.20" vs 24.09"). 185/70R15 is wider by 0.79 inches.
Can I replace 165/70R15 with 185/70R15?
It is not recommended without checking carefully. The diameter difference is +4.6%, 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 185/70R15 change my speedometer?
When your speedometer reads 60 mph with 185/70R15 fitted (calibrated for 165/70R15), your real speed is 62.7 mph. Your odometer will under-count miles by about 4.6%.
Will 185/70R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.55 inches of ground clearance at the axle.

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