Tire Size Box

235/75R15 vs 255/75R15

255/75R15 compared with 235/75R15

+4.1% diameter, +0.8" width

255/75R15 is 30.06" tall vs 28.88". More than the 3% rule of thumb, so check carefully before switching.

28.9"15" rim6.9"9.3" wide
235/75R15 (solid) compared with 255/75R15 (dashed outline), drawn to scale

With 255/75R15 tires, when your speedometer says 60 mph you are really going

62.5 mph

255/75R15 is +1.18 inches (+4.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/75R15255/75R15Difference%
Overall diameter28.88"30.06"+1.18"+4.1%
Section width9.25"10.04"+0.79"+8.5%
Sidewall height6.94"7.53"+0.59"+8.5%
Circumference90.72"94.43"+3.71"+4.1%
Revolutions per mile698.4670.9−27.4−3.9%

Speedometer difference

If your vehicle came with 235/75R15 and you fit 255/75R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.6 mph+1.6 mph
50 mph52.0 mph+2.0 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, 235/75R15 or 255/75R15?
255/75R15 is taller by 1.18 inches (30.06" vs 28.88"). 255/75R15 is wider by 0.79 inches.
Can I replace 235/75R15 with 255/75R15?
It is not recommended without checking carefully. The diameter difference is +4.1%, 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 255/75R15 change my speedometer?
When your speedometer reads 60 mph with 255/75R15 fitted (calibrated for 235/75R15), your real speed is 62.5 mph. Your odometer will under-count miles by about 4.1%.
Will 255/75R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.59 inches of ground clearance at the axle.

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