Tire Size Box

235/65R18 vs 235/70R18

235/70R18 compared with 235/65R18

+3.1% diameter, 0.0" width

235/70R18 is 30.95" tall vs 30.03". More than the 3% rule of thumb, so check carefully before switching.

30.0"18" rim6.0"9.3" wide
235/65R18 (solid) compared with 235/70R18 (dashed outline), drawn to scale

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

61.8 mph

235/70R18 is +0.93 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/65R18235/70R18Difference%
Overall diameter30.03"30.95"+0.93"+3.1%
Section width9.25"9.25"0.00"0.0%
Sidewall height6.01"6.48"+0.46"+7.7%
Circumference94.33"97.24"+2.91"+3.1%
Revolutions per mile671.7651.6−20.1−3.0%

Speedometer difference

If your vehicle came with 235/65R18 and you fit 235/70R18, 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 mph72.2 mph+2.2 mph
75 mph77.3 mph+2.3 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 235/65R18 or 235/70R18?
235/70R18 is taller by 0.93 inches (30.95" vs 30.03"). 235/65R18 is the same width.
Can I replace 235/65R18 with 235/70R18?
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 235/70R18 change my speedometer?
When your speedometer reads 60 mph with 235/70R18 fitted (calibrated for 235/65R18), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.1%.
Will 235/70R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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