Tire Size Box

235/60R18 vs 235/70R18

235/70R18 compared with 235/60R18

+6.4% diameter, 0.0" width

235/70R18 is 30.95" tall vs 29.10". More than the 3% rule of thumb, so check carefully before switching.

29.1"18" rim5.6"9.3" wide
235/60R18 (solid) compared with 235/70R18 (dashed outline), drawn to scale

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

63.8 mph

235/70R18 is +1.85 inches (+6.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/60R18235/70R18Difference%
Overall diameter29.10"30.95"+1.85"+6.4%
Section width9.25"9.25"0.00"0.0%
Sidewall height5.55"6.48"+0.93"+16.7%
Circumference91.43"97.24"+5.81"+6.4%
Revolutions per mile693.0651.6−41.4−6.0%

Speedometer difference

If your vehicle came with 235/60R18 and you fit 235/70R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph31.9 mph+1.9 mph
40 mph42.5 mph+2.5 mph
50 mph53.2 mph+3.2 mph
60 mph63.8 mph+3.8 mph
65 mph69.1 mph+4.1 mph
70 mph74.5 mph+4.5 mph
75 mph79.8 mph+4.8 mph
80 mph85.1 mph+5.1 mph

Each size on its own

Questions

Which is bigger, 235/60R18 or 235/70R18?
235/70R18 is taller by 1.85 inches (30.95" vs 29.10"). 235/60R18 is the same width.
Can I replace 235/60R18 with 235/70R18?
It is not recommended without checking carefully. The diameter difference is +6.4%, 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 235/60R18), your real speed is 63.8 mph. Your odometer will under-count miles by about 6.4%.
Will 235/70R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.93 inches of ground clearance at the axle.

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