Tire Size Box

215/70R18 vs 235/70R18

235/70R18 compared with 215/70R18

+3.7% diameter, +0.8" width

235/70R18 is 30.95" tall vs 29.85". More than the 3% rule of thumb, so check carefully before switching.

29.9"18" rim5.9"8.5" wide
215/70R18 (solid) compared with 235/70R18 (dashed outline), drawn to scale

With 235/70R18 tires, when your speedometer says 60 mph you are really going

62.2 mph

235/70R18 is +1.10 inches (+3.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

215/70R18235/70R18Difference%
Overall diameter29.85"30.95"+1.10"+3.7%
Section width8.46"9.25"+0.79"+9.3%
Sidewall height5.93"6.48"+0.55"+9.3%
Circumference93.78"97.24"+3.46"+3.7%
Revolutions per mile675.6651.6−24.1−3.6%

Speedometer difference

If your vehicle came with 215/70R18 and you fit 235/70R18, 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 mph83.0 mph+3.0 mph

Each size on its own

Questions

Which is bigger, 215/70R18 or 235/70R18?
235/70R18 is taller by 1.10 inches (30.95" vs 29.85"). 235/70R18 is wider by 0.79 inches.
Can I replace 215/70R18 with 235/70R18?
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 235/70R18 change my speedometer?
When your speedometer reads 60 mph with 235/70R18 fitted (calibrated for 215/70R18), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.7%.
Will 235/70R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.55 inches of ground clearance at the axle.

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