Tire Size Box

235/75R17 vs 255/75R17

255/75R17 compared with 235/75R17

+3.8% diameter, +0.8" width

255/75R17 is 32.06" tall vs 30.88". More than the 3% rule of thumb, so check carefully before switching.

30.9"17" rim6.9"9.3" wide
235/75R17 (solid) compared with 255/75R17 (dashed outline), drawn to scale

With 255/75R17 tires, when your speedometer says 60 mph you are really going

62.3 mph

255/75R17 is +1.18 inches (+3.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/75R17255/75R17Difference%
Overall diameter30.88"32.06"+1.18"+3.8%
Section width9.25"10.04"+0.79"+8.5%
Sidewall height6.94"7.53"+0.59"+8.5%
Circumference97.01"100.72"+3.71"+3.8%
Revolutions per mile653.2629.1−24.1−3.7%

Speedometer difference

If your vehicle came with 235/75R17 and you fit 255/75R17, 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 mph77.9 mph+2.9 mph
80 mph83.1 mph+3.1 mph

Each size on its own

Questions

Which is bigger, 235/75R17 or 255/75R17?
255/75R17 is taller by 1.18 inches (32.06" vs 30.88"). 255/75R17 is wider by 0.79 inches.
Can I replace 235/75R17 with 255/75R17?
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 255/75R17 change my speedometer?
When your speedometer reads 60 mph with 255/75R17 fitted (calibrated for 235/75R17), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.8%.
Will 255/75R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.59 inches of ground clearance at the axle.

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