Tire Size Box

175/70R15 vs 175/80R15

175/80R15 compared with 175/70R15

+5.6% diameter, 0.0" width

175/80R15 is 26.02" tall vs 24.65". More than the 3% rule of thumb, so check carefully before switching.

24.6"15" rim4.8"6.9" wide
175/70R15 (solid) compared with 175/80R15 (dashed outline), drawn to scale

With 175/80R15 tires, when your speedometer says 60 mph you are really going

63.4 mph

175/80R15 is +1.38 inches (+5.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

175/70R15175/80R15Difference%
Overall diameter24.65"26.02"+1.38"+5.6%
Section width6.89"6.89"0.00"0.0%
Sidewall height4.82"5.51"+0.69"+14.3%
Circumference77.43"81.76"+4.33"+5.6%
Revolutions per mile818.3775.0−43.3−5.3%

Speedometer difference

If your vehicle came with 175/70R15 and you fit 175/80R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.1 mph+1.1 mph
30 mph31.7 mph+1.7 mph
40 mph42.2 mph+2.2 mph
50 mph52.8 mph+2.8 mph
60 mph63.4 mph+3.4 mph
65 mph68.6 mph+3.6 mph
70 mph73.9 mph+3.9 mph
75 mph79.2 mph+4.2 mph
80 mph84.5 mph+4.5 mph

Each size on its own

Questions

Which is bigger, 175/70R15 or 175/80R15?
175/80R15 is taller by 1.38 inches (26.02" vs 24.65"). 175/70R15 is the same width.
Can I replace 175/70R15 with 175/80R15?
It is not recommended without checking carefully. The diameter difference is +5.6%, 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 175/80R15 change my speedometer?
When your speedometer reads 60 mph with 175/80R15 fitted (calibrated for 175/70R15), your real speed is 63.4 mph. Your odometer will under-count miles by about 5.6%.
Will 175/80R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.69 inches of ground clearance at the axle.

Other comparisons