Tire Size Box

235/60R20 vs 255/60R20

255/60R20 compared with 235/60R20

+3.0% diameter, +0.8" width

255/60R20 is 32.05" tall vs 31.10". More than the 3% rule of thumb, so check carefully before switching.

31.1"20" rim5.6"9.3" wide
235/60R20 (solid) compared with 255/60R20 (dashed outline), drawn to scale

With 255/60R20 tires, when your speedometer says 60 mph you are really going

61.8 mph

255/60R20 is +0.94 inches (+3.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/60R20255/60R20Difference%
Overall diameter31.10"32.05"+0.94"+3.0%
Section width9.25"10.04"+0.79"+8.5%
Sidewall height5.55"6.02"+0.47"+8.5%
Circumference97.71"100.68"+2.97"+3.0%
Revolutions per mile648.4629.3−19.1−2.9%

Speedometer difference

If your vehicle came with 235/60R20 and you fit 255/60R20, 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, 235/60R20 or 255/60R20?
255/60R20 is taller by 0.94 inches (32.05" vs 31.10"). 255/60R20 is wider by 0.79 inches.
Can I replace 235/60R20 with 255/60R20?
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 255/60R20 change my speedometer?
When your speedometer reads 60 mph with 255/60R20 fitted (calibrated for 235/60R20), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.0%.
Will 255/60R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.47 inches of ground clearance at the axle.

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