Tire Size Box

235/45R15 vs 255/45R15

255/45R15 compared with 235/45R15

+3.0% diameter, +0.8" width

255/45R15 is 24.04" tall vs 23.33". More than the 3% rule of thumb, so check carefully before switching.

23.3"15" rim4.2"9.3" wide
235/45R15 (solid) compared with 255/45R15 (dashed outline), drawn to scale

With 255/45R15 tires, when your speedometer says 60 mph you are really going

61.8 mph

255/45R15 is +0.71 inches (+3.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/45R15255/45R15Difference%
Overall diameter23.33"24.04"+0.71"+3.0%
Section width9.25"10.04"+0.79"+8.5%
Sidewall height4.16"4.52"+0.35"+8.5%
Circumference73.28"75.51"+2.23"+3.0%
Revolutions per mile864.6839.1−25.5−2.9%

Speedometer difference

If your vehicle came with 235/45R15 and you fit 255/45R15, 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 mph61.8 mph+1.8 mph
65 mph67.0 mph+2.0 mph
70 mph72.1 mph+2.1 mph
75 mph77.3 mph+2.3 mph
80 mph82.4 mph+2.4 mph

Each size on its own

Questions

Which is bigger, 235/45R15 or 255/45R15?
255/45R15 is taller by 0.71 inches (24.04" vs 23.33"). 255/45R15 is wider by 0.79 inches.
Can I replace 235/45R15 with 255/45R15?
It is not recommended without checking carefully. The diameter difference is +3.0%, 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 255/45R15 change my speedometer?
When your speedometer reads 60 mph with 255/45R15 fitted (calibrated for 235/45R15), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.0%.
Will 255/45R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.35 inches of ground clearance at the axle.

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