Tire Size Box

215/75R18 vs 235/75R18

235/75R18 compared with 215/75R18

+3.8% diameter, +0.8" width

235/75R18 is 31.88" tall vs 30.70". More than the 3% rule of thumb, so check carefully before switching.

30.7"18" rim6.3"8.5" wide
215/75R18 (solid) compared with 235/75R18 (dashed outline), drawn to scale

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

62.3 mph

235/75R18 is +1.18 inches (+3.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

215/75R18235/75R18Difference%
Overall diameter30.70"31.88"+1.18"+3.8%
Section width8.46"9.25"+0.79"+9.3%
Sidewall height6.35"6.94"+0.59"+9.3%
Circumference96.44"100.15"+3.71"+3.8%
Revolutions per mile657.0632.7−24.3−3.7%

Speedometer difference

If your vehicle came with 215/75R18 and you fit 235/75R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.5 mph+1.5 mph
50 mph51.9 mph+1.9 mph
60 mph62.3 mph+2.3 mph
65 mph67.5 mph+2.5 mph
70 mph72.7 mph+2.7 mph
75 mph77.9 mph+2.9 mph
80 mph83.1 mph+3.1 mph

Each size on its own

Questions

Which is bigger, 215/75R18 or 235/75R18?
235/75R18 is taller by 1.18 inches (31.88" vs 30.70"). 235/75R18 is wider by 0.79 inches.
Can I replace 215/75R18 with 235/75R18?
It is not recommended without checking carefully. The diameter difference is +3.8%, 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 235/75R18 change my speedometer?
When your speedometer reads 60 mph with 235/75R18 fitted (calibrated for 215/75R18), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.8%.
Will 235/75R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.59 inches of ground clearance at the axle.

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