Tire Size Box

235/65R17 vs 255/65R17

255/65R17 compared with 235/65R17

+3.5% diameter, +0.8" width

255/65R17 is 30.05" tall vs 29.03". More than the 3% rule of thumb, so check carefully before switching.

29.0"17" rim6.0"9.3" wide
235/65R17 (solid) compared with 255/65R17 (dashed outline), drawn to scale

With 255/65R17 tires, when your speedometer says 60 mph you are really going

62.1 mph

255/65R17 is +1.02 inches (+3.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/65R17255/65R17Difference%
Overall diameter29.03"30.05"+1.02"+3.5%
Section width9.25"10.04"+0.79"+8.5%
Sidewall height6.01"6.53"+0.51"+8.5%
Circumference91.19"94.41"+3.22"+3.5%
Revolutions per mile694.8671.1−23.7−3.4%

Speedometer difference

If your vehicle came with 235/65R17 and you fit 255/65R17, 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 mph62.1 mph+2.1 mph
65 mph67.3 mph+2.3 mph
70 mph72.5 mph+2.5 mph
75 mph77.6 mph+2.6 mph
80 mph82.8 mph+2.8 mph

Each size on its own

Questions

Which is bigger, 235/65R17 or 255/65R17?
255/65R17 is taller by 1.02 inches (30.05" vs 29.03"). 255/65R17 is wider by 0.79 inches.
Can I replace 235/65R17 with 255/65R17?
It is not recommended without checking carefully. The diameter difference is +3.5%, 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 255/65R17 change my speedometer?
When your speedometer reads 60 mph with 255/65R17 fitted (calibrated for 235/65R17), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.5%.
Will 255/65R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.51 inches of ground clearance at the axle.

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