Tire Size Box

235/70R17 vs 255/70R17

255/70R17 compared with 235/70R17

+3.7% diameter, +0.8" width

255/70R17 is 31.06" tall vs 29.95". More than the 3% rule of thumb, so check carefully before switching.

30.0"17" rim6.5"9.3" wide
235/70R17 (solid) compared with 255/70R17 (dashed outline), drawn to scale

With 255/70R17 tires, when your speedometer says 60 mph you are really going

62.2 mph

255/70R17 is +1.10 inches (+3.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/70R17255/70R17Difference%
Overall diameter29.95"31.06"+1.10"+3.7%
Section width9.25"10.04"+0.79"+8.5%
Sidewall height6.48"7.03"+0.55"+8.5%
Circumference94.10"97.56"+3.46"+3.7%
Revolutions per mile673.3649.4−23.9−3.5%

Speedometer difference

If your vehicle came with 235/70R17 and you fit 255/70R17, 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 mph41.5 mph+1.5 mph
50 mph51.8 mph+1.8 mph
60 mph62.2 mph+2.2 mph
65 mph67.4 mph+2.4 mph
70 mph72.6 mph+2.6 mph
75 mph77.8 mph+2.8 mph
80 mph82.9 mph+2.9 mph

Each size on its own

Questions

Which is bigger, 235/70R17 or 255/70R17?
255/70R17 is taller by 1.10 inches (31.06" vs 29.95"). 255/70R17 is wider by 0.79 inches.
Can I replace 235/70R17 with 255/70R17?
It is not recommended without checking carefully. The diameter difference is +3.7%, 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 255/70R17 change my speedometer?
When your speedometer reads 60 mph with 255/70R17 fitted (calibrated for 235/70R17), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.7%.
Will 255/70R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.55 inches of ground clearance at the axle.

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