Tire Size Box

255/55R15 vs 275/55R15

275/55R15 compared with 255/55R15

+3.3% diameter, +0.8" width

275/55R15 is 26.91" 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 275/55R15 (dashed outline), drawn to scale

With 275/55R15 tires, when your speedometer says 60 mph you are really going

62.0 mph

275/55R15 is +0.87 inches (+3.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/55R15275/55R15Difference%
Overall diameter26.04"26.91"+0.87"+3.3%
Section width10.04"10.83"+0.79"+7.8%
Sidewall height5.52"5.95"+0.43"+7.8%
Circumference81.82"84.54"+2.72"+3.3%
Revolutions per mile774.4749.5−24.9−3.2%

Speedometer difference

If your vehicle came with 255/55R15 and you fit 275/55R15, 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 mph41.3 mph+1.3 mph
50 mph51.7 mph+1.7 mph
60 mph62.0 mph+2.0 mph
65 mph67.2 mph+2.2 mph
70 mph72.3 mph+2.3 mph
75 mph77.5 mph+2.5 mph
80 mph82.7 mph+2.7 mph

Each size on its own

Questions

Which is bigger, 255/55R15 or 275/55R15?
275/55R15 is taller by 0.87 inches (26.91" vs 26.04"). 275/55R15 is wider by 0.79 inches.
Can I replace 255/55R15 with 275/55R15?
It is not recommended without checking carefully. The diameter difference is +3.3%, 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 275/55R15 change my speedometer?
When your speedometer reads 60 mph with 275/55R15 fitted (calibrated for 255/55R15), your real speed is 62.0 mph. Your odometer will under-count miles by about 3.3%.
Will 275/55R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.43 inches of ground clearance at the axle.

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