Tire Size Box

235/70R15 vs 255/70R15

255/70R15 compared with 235/70R15

+3.9% diameter, +0.8" width

255/70R15 is 29.06" tall vs 27.95". More than the 3% rule of thumb, so check carefully before switching.

28.0"15" rim6.5"9.3" wide
235/70R15 (solid) compared with 255/70R15 (dashed outline), drawn to scale

With 255/70R15 tires, when your speedometer says 60 mph you are really going

62.4 mph

255/70R15 is +1.10 inches (+3.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/70R15255/70R15Difference%
Overall diameter27.95"29.06"+1.10"+3.9%
Section width9.25"10.04"+0.79"+8.5%
Sidewall height6.48"7.03"+0.55"+8.5%
Circumference87.82"91.28"+3.46"+3.9%
Revolutions per mile721.5694.1−27.4−3.8%

Speedometer difference

If your vehicle came with 235/70R15 and you fit 255/70R15, 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 mph62.4 mph+2.4 mph
65 mph67.6 mph+2.6 mph
70 mph72.8 mph+2.8 mph
75 mph78.0 mph+3.0 mph
80 mph83.2 mph+3.2 mph

Each size on its own

Questions

Which is bigger, 235/70R15 or 255/70R15?
255/70R15 is taller by 1.10 inches (29.06" vs 27.95"). 255/70R15 is wider by 0.79 inches.
Can I replace 235/70R15 with 255/70R15?
It is not recommended without checking carefully. The diameter difference is +3.9%, 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 255/70R15 change my speedometer?
When your speedometer reads 60 mph with 255/70R15 fitted (calibrated for 235/70R15), your real speed is 62.4 mph. Your odometer will under-count miles by about 3.9%.
Will 255/70R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.55 inches of ground clearance at the axle.

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