Tire Size Box

185/65R15 vs 185/70R15

185/70R15 compared with 185/65R15

+3.0% diameter, 0.0" width

185/70R15 is 25.20" tall vs 24.47". Within the 3% rule, so usually interchangeable.

24.5"15" rim4.7"7.3" wide
185/65R15 (solid) compared with 185/70R15 (dashed outline), drawn to scale

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

61.8 mph

185/70R15 is +0.73 inches (+3.0%) in overall diameter. That is within the 3% most shops and makers allow.

185/65R15185/70R15Difference%
Overall diameter24.47"25.20"+0.73"+3.0%
Section width7.28"7.28"0.00"0.0%
Sidewall height4.73"5.10"+0.36"+7.7%
Circumference76.87"79.16"+2.29"+3.0%
Revolutions per mile824.2800.4−23.8−2.9%

Speedometer difference

If your vehicle came with 185/65R15 and you fit 185/70R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph30.9 mph+0.9 mph
40 mph41.2 mph+1.2 mph
50 mph51.5 mph+1.5 mph
60 mph61.8 mph+1.8 mph
65 mph66.9 mph+1.9 mph
70 mph72.1 mph+2.1 mph
75 mph77.2 mph+2.2 mph
80 mph82.4 mph+2.4 mph

Each size on its own

Questions

Which is bigger, 185/65R15 or 185/70R15?
185/70R15 is taller by 0.73 inches (25.20" vs 24.47"). 185/65R15 is the same width.
Can I replace 185/65R15 with 185/70R15?
Usually, yes. The diameter difference is +3.0%, inside the 3% rule of thumb most tire shops use. Check that the wider or taller tire clears your suspension and fenders, and that its load index meets your placard.
How much will 185/70R15 change my speedometer?
When your speedometer reads 60 mph with 185/70R15 fitted (calibrated for 185/65R15), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.0%.
Will 185/70R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.36 inches of ground clearance at the axle.

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