Tire Size Box

185/70R15 vs 205/70R15

205/70R15 compared with 185/70R15

+4.4% diameter, +0.8" width

205/70R15 is 26.30" tall vs 25.20". More than the 3% rule of thumb, so check carefully before switching.

25.2"15" rim5.1"7.3" wide
185/70R15 (solid) compared with 205/70R15 (dashed outline), drawn to scale

With 205/70R15 tires, when your speedometer says 60 mph you are really going

62.6 mph

205/70R15 is +1.10 inches (+4.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

185/70R15205/70R15Difference%
Overall diameter25.20"26.30"+1.10"+4.4%
Section width7.28"8.07"+0.79"+10.8%
Sidewall height5.10"5.65"+0.55"+10.8%
Circumference79.16"82.62"+3.46"+4.4%
Revolutions per mile800.4766.9−33.6−4.2%

Speedometer difference

If your vehicle came with 185/70R15 and you fit 205/70R15, 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 mph41.8 mph+1.8 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, 185/70R15 or 205/70R15?
205/70R15 is taller by 1.10 inches (26.30" vs 25.20"). 205/70R15 is wider by 0.79 inches.
Can I replace 185/70R15 with 205/70R15?
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 205/70R15 change my speedometer?
When your speedometer reads 60 mph with 205/70R15 fitted (calibrated for 185/70R15), your real speed is 62.6 mph. Your odometer will under-count miles by about 4.4%.
Will 205/70R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.55 inches of ground clearance at the axle.

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