Tire Size Box

255/60R18 vs 275/60R18

275/60R18 compared with 255/60R18

+3.1% diameter, +0.8" width

275/60R18 is 30.99" tall vs 30.05". More than the 3% rule of thumb, so check carefully before switching.

30.0"18" rim6.0"10.0" wide
255/60R18 (solid) compared with 275/60R18 (dashed outline), drawn to scale

With 275/60R18 tires, when your speedometer says 60 mph you are really going

61.9 mph

275/60R18 is +0.94 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/60R18275/60R18Difference%
Overall diameter30.05"30.99"+0.94"+3.1%
Section width10.04"10.83"+0.79"+7.8%
Sidewall height6.02"6.50"+0.47"+7.8%
Circumference94.40"97.36"+2.97"+3.1%
Revolutions per mile671.2650.7−20.5−3.0%

Speedometer difference

If your vehicle came with 255/60R18 and you fit 275/60R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph30.9 mph+0.9 mph
40 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.0 mph+2.0 mph
70 mph72.2 mph+2.2 mph
75 mph77.4 mph+2.4 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 255/60R18 or 275/60R18?
275/60R18 is taller by 0.94 inches (30.99" vs 30.05"). 275/60R18 is wider by 0.79 inches.
Can I replace 255/60R18 with 275/60R18?
It is not recommended without checking carefully. The diameter difference is +3.1%, 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 275/60R18 change my speedometer?
When your speedometer reads 60 mph with 275/60R18 fitted (calibrated for 255/60R18), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.1%.
Will 275/60R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.47 inches of ground clearance at the axle.

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