Tire Size Box

245/70R18 vs 245/75R18

245/75R18 compared with 245/70R18

+3.1% diameter, 0.0" width

245/75R18 is 32.47" tall vs 31.50". More than the 3% rule of thumb, so check carefully before switching.

31.5"18" rim6.8"9.6" wide
245/70R18 (solid) compared with 245/75R18 (dashed outline), drawn to scale

With 245/75R18 tires, when your speedometer says 60 mph you are really going

61.8 mph

245/75R18 is +0.96 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/70R18245/75R18Difference%
Overall diameter31.50"32.47"+0.96"+3.1%
Section width9.65"9.65"0.00"0.0%
Sidewall height6.75"7.23"+0.48"+7.1%
Circumference98.97"102.00"+3.03"+3.1%
Revolutions per mile640.2621.2−19.0−3.0%

Speedometer difference

If your vehicle came with 245/70R18 and you fit 245/75R18, 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 mph41.2 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, 245/70R18 or 245/75R18?
245/75R18 is taller by 0.96 inches (32.47" vs 31.50"). 245/70R18 is the same width.
Can I replace 245/70R18 with 245/75R18?
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 245/75R18 change my speedometer?
When your speedometer reads 60 mph with 245/75R18 fitted (calibrated for 245/70R18), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.1%.
Will 245/75R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.48 inches of ground clearance at the axle.

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