Tire Size Box

235/70R18 vs 235/75R18

235/75R18 compared with 235/70R18

+3.0% diameter, 0.0" width

235/75R18 is 31.88" tall vs 30.95". Within the 3% rule, so usually interchangeable.

31.0"18" rim6.5"9.3" wide
235/70R18 (solid) compared with 235/75R18 (dashed outline), drawn to scale

With 235/75R18 tires, when your speedometer says 60 mph you are really going

61.8 mph

235/75R18 is +0.93 inches (+3.0%) in overall diameter. That is within the 3% most shops and makers allow.

235/70R18235/75R18Difference%
Overall diameter30.95"31.88"+0.93"+3.0%
Section width9.25"9.25"0.00"0.0%
Sidewall height6.48"6.94"+0.46"+7.1%
Circumference97.24"100.15"+2.91"+3.0%
Revolutions per mile651.6632.7−18.9−2.9%

Speedometer difference

If your vehicle came with 235/70R18 and you fit 235/75R18, 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 mph66.9 mph+1.9 mph
70 mph72.1 mph+2.1 mph
75 mph77.2 mph+2.2 mph
80 mph82.4 mph+2.4 mph

Each size on its own

Questions

Which is bigger, 235/70R18 or 235/75R18?
235/75R18 is taller by 0.93 inches (31.88" vs 30.95"). 235/70R18 is the same width.
Can I replace 235/70R18 with 235/75R18?
Usually, yes. The diameter difference is +3.0%, inside the 3% rule of thumb most tire shops use. Check that the wider or taller tire clears your suspension and fenders, and that its load index meets your placard.
How much will 235/75R18 change my speedometer?
When your speedometer reads 60 mph with 235/75R18 fitted (calibrated for 235/70R18), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.0%.
Will 235/75R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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