Tire Size Box

255/65R20 vs 275/65R20

275/65R20 compared with 255/65R20

+3.1% diameter, +0.8" width

275/65R20 is 34.07" tall vs 33.05". More than the 3% rule of thumb, so check carefully before switching.

33.1"20" rim6.5"10.0" wide
255/65R20 (solid) compared with 275/65R20 (dashed outline), drawn to scale

With 275/65R20 tires, when your speedometer says 60 mph you are really going

61.9 mph

275/65R20 is +1.02 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/65R20275/65R20Difference%
Overall diameter33.05"34.07"+1.02"+3.1%
Section width10.04"10.83"+0.79"+7.8%
Sidewall height6.53"7.04"+0.51"+7.8%
Circumference103.83"107.05"+3.22"+3.1%
Revolutions per mile610.2591.9−18.3−3.0%

Speedometer difference

If your vehicle came with 255/65R20 and you fit 275/65R20, 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 mph41.2 mph+1.2 mph
50 mph51.5 mph+1.5 mph
60 mph61.9 mph+1.9 mph
65 mph67.0 mph+2.0 mph
70 mph72.2 mph+2.2 mph
75 mph77.3 mph+2.3 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 255/65R20 or 275/65R20?
275/65R20 is taller by 1.02 inches (34.07" vs 33.05"). 275/65R20 is wider by 0.79 inches.
Can I replace 255/65R20 with 275/65R20?
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 275/65R20 change my speedometer?
When your speedometer reads 60 mph with 275/65R20 fitted (calibrated for 255/65R20), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.1%.
Will 275/65R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.51 inches of ground clearance at the axle.

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