Tire Size Box

235/60R15 vs 255/60R15

255/60R15 compared with 235/60R15

+3.6% diameter, +0.8" width

255/60R15 is 27.05" tall vs 26.10". More than the 3% rule of thumb, so check carefully before switching.

26.1"15" rim5.6"9.3" wide
235/60R15 (solid) compared with 255/60R15 (dashed outline), drawn to scale

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

62.2 mph

255/60R15 is +0.94 inches (+3.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/60R15255/60R15Difference%
Overall diameter26.10"27.05"+0.94"+3.6%
Section width9.25"10.04"+0.79"+8.5%
Sidewall height5.55"6.02"+0.47"+8.5%
Circumference82.00"84.97"+2.97"+3.6%
Revolutions per mile772.7745.7−27.0−3.5%

Speedometer difference

If your vehicle came with 235/60R15 and you fit 255/60R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.1 mph+1.1 mph
40 mph41.4 mph+1.4 mph
50 mph51.8 mph+1.8 mph
60 mph62.2 mph+2.2 mph
65 mph67.4 mph+2.4 mph
70 mph72.5 mph+2.5 mph
75 mph77.7 mph+2.7 mph
80 mph82.9 mph+2.9 mph

Each size on its own

Questions

Which is bigger, 235/60R15 or 255/60R15?
255/60R15 is taller by 0.94 inches (27.05" vs 26.10"). 255/60R15 is wider by 0.79 inches.
Can I replace 235/60R15 with 255/60R15?
It is not recommended without checking carefully. The diameter difference is +3.6%, 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 255/60R15 change my speedometer?
When your speedometer reads 60 mph with 255/60R15 fitted (calibrated for 235/60R15), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.6%.
Will 255/60R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.47 inches of ground clearance at the axle.

Other comparisons