Tire Size Box

215/65R18 vs 235/65R18

235/65R18 compared with 215/65R18

+3.5% diameter, +0.8" width

235/65R18 is 30.03" tall vs 29.00". More than the 3% rule of thumb, so check carefully before switching.

29.0"18" rim5.5"8.5" wide
215/65R18 (solid) compared with 235/65R18 (dashed outline), drawn to scale

With 235/65R18 tires, when your speedometer says 60 mph you are really going

62.1 mph

235/65R18 is +1.02 inches (+3.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

215/65R18235/65R18Difference%
Overall diameter29.00"30.03"+1.02"+3.5%
Section width8.46"9.25"+0.79"+9.3%
Sidewall height5.50"6.01"+0.51"+9.3%
Circumference91.12"94.33"+3.22"+3.5%
Revolutions per mile695.4671.7−23.7−3.4%

Speedometer difference

If your vehicle came with 215/65R18 and you fit 235/65R18, 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 mph41.4 mph+1.4 mph
50 mph51.8 mph+1.8 mph
60 mph62.1 mph+2.1 mph
65 mph67.3 mph+2.3 mph
70 mph72.5 mph+2.5 mph
75 mph77.6 mph+2.6 mph
80 mph82.8 mph+2.8 mph

Each size on its own

Questions

Which is bigger, 215/65R18 or 235/65R18?
235/65R18 is taller by 1.02 inches (30.03" vs 29.00"). 235/65R18 is wider by 0.79 inches.
Can I replace 215/65R18 with 235/65R18?
It is not recommended without checking carefully. The diameter difference is +3.5%, 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 235/65R18 change my speedometer?
When your speedometer reads 60 mph with 235/65R18 fitted (calibrated for 215/65R18), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.5%.
Will 235/65R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.51 inches of ground clearance at the axle.

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