Tire Size Box

235/65R15 vs 255/65R15

255/65R15 compared with 235/65R15

+3.8% diameter, +0.8" width

255/65R15 is 28.05" tall vs 27.03". More than the 3% rule of thumb, so check carefully before switching.

27.0"15" rim6.0"9.3" wide
235/65R15 (solid) compared with 255/65R15 (dashed outline), drawn to scale

With 255/65R15 tires, when your speedometer says 60 mph you are really going

62.3 mph

255/65R15 is +1.02 inches (+3.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/65R15255/65R15Difference%
Overall diameter27.03"28.05"+1.02"+3.8%
Section width9.25"10.04"+0.79"+8.5%
Sidewall height6.01"6.53"+0.51"+8.5%
Circumference84.91"88.13"+3.22"+3.8%
Revolutions per mile746.2719.0−27.2−3.6%

Speedometer difference

If your vehicle came with 235/65R15 and you fit 255/65R15, 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 mph77.8 mph+2.8 mph
80 mph83.0 mph+3.0 mph

Each size on its own

Questions

Which is bigger, 235/65R15 or 255/65R15?
255/65R15 is taller by 1.02 inches (28.05" vs 27.03"). 255/65R15 is wider by 0.79 inches.
Can I replace 235/65R15 with 255/65R15?
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 255/65R15 change my speedometer?
When your speedometer reads 60 mph with 255/65R15 fitted (calibrated for 235/65R15), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.8%.
Will 255/65R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.51 inches of ground clearance at the axle.

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