Tire Size Box

255/70R18 vs 255/75R18

255/75R18 compared with 255/70R18

+3.1% diameter, 0.0" width

255/75R18 is 33.06" tall vs 32.06". More than the 3% rule of thumb, so check carefully before switching.

32.1"18" rim7.0"10.0" wide
255/70R18 (solid) compared with 255/75R18 (dashed outline), drawn to scale

With 255/75R18 tires, when your speedometer says 60 mph you are really going

61.9 mph

255/75R18 is +1.00 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/70R18255/75R18Difference%
Overall diameter32.06"33.06"+1.00"+3.1%
Section width10.04"10.04"0.00"0.0%
Sidewall height7.03"7.53"+0.50"+7.1%
Circumference100.70"103.86"+3.15"+3.1%
Revolutions per mile629.2610.1−19.1−3.0%

Speedometer difference

If your vehicle came with 255/70R18 and you fit 255/75R18, 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 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.0 mph+2.0 mph
70 mph72.2 mph+2.2 mph
75 mph77.3 mph+2.3 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 255/70R18 or 255/75R18?
255/75R18 is taller by 1.00 inches (33.06" vs 32.06"). 255/70R18 is the same width.
Can I replace 255/70R18 with 255/75R18?
It is not recommended without checking carefully. The diameter difference is +3.1%, 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 255/75R18 change my speedometer?
When your speedometer reads 60 mph with 255/75R18 fitted (calibrated for 255/70R18), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.1%.
Will 255/75R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.50 inches of ground clearance at the axle.

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