Tire Size Box

255/70R15 vs 275/70R15

275/70R15 compared with 255/70R15

+3.8% diameter, +0.8" width

275/70R15 is 30.16" tall vs 29.06". More than the 3% rule of thumb, so check carefully before switching.

29.1"15" rim7.0"10.0" wide
255/70R15 (solid) compared with 275/70R15 (dashed outline), drawn to scale

With 275/70R15 tires, when your speedometer says 60 mph you are really going

62.3 mph

275/70R15 is +1.10 inches (+3.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/70R15275/70R15Difference%
Overall diameter29.06"30.16"+1.10"+3.8%
Section width10.04"10.83"+0.79"+7.8%
Sidewall height7.03"7.58"+0.55"+7.8%
Circumference91.28"94.74"+3.46"+3.8%
Revolutions per mile694.1668.8−25.4−3.7%

Speedometer difference

If your vehicle came with 255/70R15 and you fit 275/70R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.1 mph+1.1 mph
40 mph41.5 mph+1.5 mph
50 mph51.9 mph+1.9 mph
60 mph62.3 mph+2.3 mph
65 mph67.5 mph+2.5 mph
70 mph72.7 mph+2.7 mph
75 mph77.8 mph+2.8 mph
80 mph83.0 mph+3.0 mph

Each size on its own

Questions

Which is bigger, 255/70R15 or 275/70R15?
275/70R15 is taller by 1.10 inches (30.16" vs 29.06"). 275/70R15 is wider by 0.79 inches.
Can I replace 255/70R15 with 275/70R15?
It is not recommended without checking carefully. The diameter difference is +3.8%, 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 275/70R15 change my speedometer?
When your speedometer reads 60 mph with 275/70R15 fitted (calibrated for 255/70R15), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.8%.
Will 275/70R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.55 inches of ground clearance at the axle.

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