Tire Size Box

235/55R15 vs 255/55R15

255/55R15 compared with 235/55R15

+3.4% diameter, +0.8" width

255/55R15 is 26.04" tall vs 25.18". More than the 3% rule of thumb, so check carefully before switching.

25.2"15" rim5.1"9.3" wide
235/55R15 (solid) compared with 255/55R15 (dashed outline), drawn to scale

With 255/55R15 tires, when your speedometer says 60 mph you are really going

62.1 mph

255/55R15 is +0.87 inches (+3.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/55R15255/55R15Difference%
Overall diameter25.18"26.04"+0.87"+3.4%
Section width9.25"10.04"+0.79"+8.5%
Sidewall height5.09"5.52"+0.43"+8.5%
Circumference79.10"81.82"+2.72"+3.4%
Revolutions per mile801.0774.4−26.6−3.3%

Speedometer difference

If your vehicle came with 235/55R15 and you fit 255/55R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.4 mph+1.4 mph
50 mph51.7 mph+1.7 mph
60 mph62.1 mph+2.1 mph
65 mph67.2 mph+2.2 mph
70 mph72.4 mph+2.4 mph
75 mph77.6 mph+2.6 mph
80 mph82.8 mph+2.8 mph

Each size on its own

Questions

Which is bigger, 235/55R15 or 255/55R15?
255/55R15 is taller by 0.87 inches (26.04" vs 25.18"). 255/55R15 is wider by 0.79 inches.
Can I replace 235/55R15 with 255/55R15?
It is not recommended without checking carefully. The diameter difference is +3.4%, 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 255/55R15 change my speedometer?
When your speedometer reads 60 mph with 255/55R15 fitted (calibrated for 235/55R15), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.4%.
Will 255/55R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.43 inches of ground clearance at the axle.

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