Tire Size Box

235/55R17 vs 255/55R17

255/55R17 compared with 235/55R17

+3.2% diameter, +0.8" width

255/55R17 is 28.04" tall vs 27.18". More than the 3% rule of thumb, so check carefully before switching.

27.2"17" rim5.1"9.3" wide
235/55R17 (solid) compared with 255/55R17 (dashed outline), drawn to scale

With 255/55R17 tires, when your speedometer says 60 mph you are really going

61.9 mph

255/55R17 is +0.87 inches (+3.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/55R17255/55R17Difference%
Overall diameter27.18"28.04"+0.87"+3.2%
Section width9.25"10.04"+0.79"+8.5%
Sidewall height5.09"5.52"+0.43"+8.5%
Circumference85.38"88.10"+2.72"+3.2%
Revolutions per mile742.1719.2−22.9−3.1%

Speedometer difference

If your vehicle came with 235/55R17 and you fit 255/55R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph31.0 mph+1.0 mph
40 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.1 mph+2.1 mph
70 mph72.2 mph+2.2 mph
75 mph77.4 mph+2.4 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 235/55R17 or 255/55R17?
255/55R17 is taller by 0.87 inches (28.04" vs 27.18"). 255/55R17 is wider by 0.79 inches.
Can I replace 235/55R17 with 255/55R17?
It is not recommended without checking carefully. The diameter difference is +3.2%, 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 255/55R17 change my speedometer?
When your speedometer reads 60 mph with 255/55R17 fitted (calibrated for 235/55R17), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.2%.
Will 255/55R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.43 inches of ground clearance at the axle.

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