Tire Size Box

255/55R15 vs 255/65R15

255/65R15 compared with 255/55R15

+7.7% diameter, 0.0" width

255/65R15 is 28.05" tall vs 26.04". More than the 3% rule of thumb, so check carefully before switching.

26.0"15" rim5.5"10.0" wide
255/55R15 (solid) compared with 255/65R15 (dashed outline), drawn to scale

With 255/65R15 tires, when your speedometer says 60 mph you are really going

64.6 mph

255/65R15 is +2.01 inches (+7.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/55R15255/65R15Difference%
Overall diameter26.04"28.05"+2.01"+7.7%
Section width10.04"10.04"0.00"0.0%
Sidewall height5.52"6.53"+1.00"+18.2%
Circumference81.82"88.13"+6.31"+7.7%
Revolutions per mile774.4719.0−55.4−7.2%

Speedometer difference

If your vehicle came with 255/55R15 and you fit 255/65R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.5 mph+1.5 mph
30 mph32.3 mph+2.3 mph
40 mph43.1 mph+3.1 mph
50 mph53.9 mph+3.9 mph
60 mph64.6 mph+4.6 mph
65 mph70.0 mph+5.0 mph
70 mph75.4 mph+5.4 mph
75 mph80.8 mph+5.8 mph
80 mph86.2 mph+6.2 mph

Each size on its own

Questions

Which is bigger, 255/55R15 or 255/65R15?
255/65R15 is taller by 2.01 inches (28.05" vs 26.04"). 255/55R15 is the same width.
Can I replace 255/55R15 with 255/65R15?
It is not recommended without checking carefully. The diameter difference is +7.7%, 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 255/65R15 change my speedometer?
When your speedometer reads 60 mph with 255/65R15 fitted (calibrated for 255/55R15), your real speed is 64.6 mph. Your odometer will under-count miles by about 7.7%.
Will 255/65R15 lift my vehicle?
Ride height changes by half the diameter difference: +1.00 inches of ground clearance at the axle.

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