Tire Size Box

255/75R15 vs 275/75R15

275/75R15 compared with 255/75R15

+3.9% diameter, +0.8" width

275/75R15 is 31.24" tall vs 30.06". More than the 3% rule of thumb, so check carefully before switching.

30.1"15" rim7.5"10.0" wide
255/75R15 (solid) compared with 275/75R15 (dashed outline), drawn to scale

With 275/75R15 tires, when your speedometer says 60 mph you are really going

62.4 mph

275/75R15 is +1.18 inches (+3.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/75R15275/75R15Difference%
Overall diameter30.06"31.24"+1.18"+3.9%
Section width10.04"10.83"+0.79"+7.8%
Sidewall height7.53"8.12"+0.59"+7.8%
Circumference94.43"98.14"+3.71"+3.9%
Revolutions per mile670.9645.6−25.4−3.8%

Speedometer difference

If your vehicle came with 255/75R15 and you fit 275/75R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.6 mph+1.6 mph
50 mph52.0 mph+2.0 mph
60 mph62.4 mph+2.4 mph
65 mph67.6 mph+2.6 mph
70 mph72.8 mph+2.8 mph
75 mph77.9 mph+2.9 mph
80 mph83.1 mph+3.1 mph

Each size on its own

Questions

Which is bigger, 255/75R15 or 275/75R15?
275/75R15 is taller by 1.18 inches (31.24" vs 30.06"). 275/75R15 is wider by 0.79 inches.
Can I replace 255/75R15 with 275/75R15?
It is not recommended without checking carefully. The diameter difference is +3.9%, 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 275/75R15 change my speedometer?
When your speedometer reads 60 mph with 275/75R15 fitted (calibrated for 255/75R15), your real speed is 62.4 mph. Your odometer will under-count miles by about 3.9%.
Will 275/75R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.59 inches of ground clearance at the axle.

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