Tire Size Box

185/70R15 vs 185/80R15

185/80R15 compared with 185/70R15

+5.8% diameter, 0.0" width

185/80R15 is 26.65" 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 185/80R15 (dashed outline), drawn to scale

With 185/80R15 tires, when your speedometer says 60 mph you are really going

63.5 mph

185/80R15 is +1.46 inches (+5.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

185/70R15185/80R15Difference%
Overall diameter25.20"26.65"+1.46"+5.8%
Section width7.28"7.28"0.00"0.0%
Sidewall height5.10"5.83"+0.73"+14.3%
Circumference79.16"83.73"+4.58"+5.8%
Revolutions per mile800.4756.7−43.7−5.5%

Speedometer difference

If your vehicle came with 185/70R15 and you fit 185/80R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.2 mph+1.2 mph
30 mph31.7 mph+1.7 mph
40 mph42.3 mph+2.3 mph
50 mph52.9 mph+2.9 mph
60 mph63.5 mph+3.5 mph
65 mph68.8 mph+3.8 mph
70 mph74.0 mph+4.0 mph
75 mph79.3 mph+4.3 mph
80 mph84.6 mph+4.6 mph

Each size on its own

Questions

Which is bigger, 185/70R15 or 185/80R15?
185/80R15 is taller by 1.46 inches (26.65" vs 25.20"). 185/70R15 is the same width.
Can I replace 185/70R15 with 185/80R15?
It is not recommended without checking carefully. The diameter difference is +5.8%, 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 185/80R15 change my speedometer?
When your speedometer reads 60 mph with 185/80R15 fitted (calibrated for 185/70R15), your real speed is 63.5 mph. Your odometer will under-count miles by about 5.8%.
Will 185/80R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.73 inches of ground clearance at the axle.

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