Tire Size Box

185/65R15 vs 185/75R15

185/75R15 compared with 185/65R15

+6.0% diameter, 0.0" width

185/75R15 is 25.93" tall vs 24.47". More than the 3% rule of thumb, so check carefully before switching.

24.5"15" rim4.7"7.3" wide
185/65R15 (solid) compared with 185/75R15 (dashed outline), drawn to scale

With 185/75R15 tires, when your speedometer says 60 mph you are really going

63.6 mph

185/75R15 is +1.46 inches (+6.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

185/65R15185/75R15Difference%
Overall diameter24.47"25.93"+1.46"+6.0%
Section width7.28"7.28"0.00"0.0%
Sidewall height4.73"5.46"+0.73"+15.4%
Circumference76.87"81.45"+4.58"+6.0%
Revolutions per mile824.2777.9−46.3−5.6%

Speedometer difference

If your vehicle came with 185/65R15 and you fit 185/75R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.2 mph+1.2 mph
30 mph31.8 mph+1.8 mph
40 mph42.4 mph+2.4 mph
50 mph53.0 mph+3.0 mph
60 mph63.6 mph+3.6 mph
65 mph68.9 mph+3.9 mph
70 mph74.2 mph+4.2 mph
75 mph79.5 mph+4.5 mph
80 mph84.8 mph+4.8 mph

Each size on its own

Questions

Which is bigger, 185/65R15 or 185/75R15?
185/75R15 is taller by 1.46 inches (25.93" vs 24.47"). 185/65R15 is the same width.
Can I replace 185/65R15 with 185/75R15?
It is not recommended without checking carefully. The diameter difference is +6.0%, 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 185/75R15 change my speedometer?
When your speedometer reads 60 mph with 185/75R15 fitted (calibrated for 185/65R15), your real speed is 63.6 mph. Your odometer will under-count miles by about 6.0%.
Will 185/75R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.73 inches of ground clearance at the axle.

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