Tire Size Box

185/55R15 vs 185/65R15

185/65R15 compared with 185/55R15

+6.3% diameter, 0.0" width

185/65R15 is 24.47" tall vs 23.01". More than the 3% rule of thumb, so check carefully before switching.

23.0"15" rim4.0"7.3" wide
185/55R15 (solid) compared with 185/65R15 (dashed outline), drawn to scale

With 185/65R15 tires, when your speedometer says 60 mph you are really going

63.8 mph

185/65R15 is +1.46 inches (+6.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

185/55R15185/65R15Difference%
Overall diameter23.01"24.47"+1.46"+6.3%
Section width7.28"7.28"0.00"0.0%
Sidewall height4.01"4.73"+0.73"+18.2%
Circumference72.29"76.87"+4.58"+6.3%
Revolutions per mile876.4824.2−52.2−6.0%

Speedometer difference

If your vehicle came with 185/55R15 and you fit 185/65R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph31.9 mph+1.9 mph
40 mph42.5 mph+2.5 mph
50 mph53.2 mph+3.2 mph
60 mph63.8 mph+3.8 mph
65 mph69.1 mph+4.1 mph
70 mph74.4 mph+4.4 mph
75 mph79.7 mph+4.7 mph
80 mph85.1 mph+5.1 mph

Each size on its own

Questions

Which is bigger, 185/55R15 or 185/65R15?
185/65R15 is taller by 1.46 inches (24.47" vs 23.01"). 185/55R15 is the same width.
Can I replace 185/55R15 with 185/65R15?
It is not recommended without checking carefully. The diameter difference is +6.3%, 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 185/65R15 change my speedometer?
When your speedometer reads 60 mph with 185/65R15 fitted (calibrated for 185/55R15), your real speed is 63.8 mph. Your odometer will under-count miles by about 6.3%.
Will 185/65R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.73 inches of ground clearance at the axle.

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