Tire Size Box

255/85R15 vs 275/85R15

275/85R15 compared with 255/85R15

+4.2% diameter, +0.8" width

275/85R15 is 33.41" tall vs 32.07". More than the 3% rule of thumb, so check carefully before switching.

32.1"15" rim8.5"10.0" wide
255/85R15 (solid) compared with 275/85R15 (dashed outline), drawn to scale

With 275/85R15 tires, when your speedometer says 60 mph you are really going

62.5 mph

275/85R15 is +1.34 inches (+4.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/85R15275/85R15Difference%
Overall diameter32.07"33.41"+1.34"+4.2%
Section width10.04"10.83"+0.79"+7.8%
Sidewall height8.53"9.20"+0.67"+7.8%
Circumference100.74"104.95"+4.21"+4.2%
Revolutions per mile628.9603.7−25.2−4.0%

Speedometer difference

If your vehicle came with 255/85R15 and you fit 275/85R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.3 mph+1.3 mph
40 mph41.7 mph+1.7 mph
50 mph52.1 mph+2.1 mph
60 mph62.5 mph+2.5 mph
65 mph67.7 mph+2.7 mph
70 mph72.9 mph+2.9 mph
75 mph78.1 mph+3.1 mph
80 mph83.3 mph+3.3 mph

Each size on its own

Questions

Which is bigger, 255/85R15 or 275/85R15?
275/85R15 is taller by 1.34 inches (33.41" vs 32.07"). 275/85R15 is wider by 0.79 inches.
Can I replace 255/85R15 with 275/85R15?
It is not recommended without checking carefully. The diameter difference is +4.2%, 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 275/85R15 change my speedometer?
When your speedometer reads 60 mph with 275/85R15 fitted (calibrated for 255/85R15), your real speed is 62.5 mph. Your odometer will under-count miles by about 4.2%.
Will 275/85R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.67 inches of ground clearance at the axle.

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