Tire Size Box

255/60R18 vs 255/70R18

255/70R18 compared with 255/60R18

+6.7% diameter, 0.0" width

255/70R18 is 32.06" tall vs 30.05". More than the 3% rule of thumb, so check carefully before switching.

30.0"18" rim6.0"10.0" wide
255/60R18 (solid) compared with 255/70R18 (dashed outline), drawn to scale

With 255/70R18 tires, when your speedometer says 60 mph you are really going

64.0 mph

255/70R18 is +2.01 inches (+6.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/60R18255/70R18Difference%
Overall diameter30.05"32.06"+2.01"+6.7%
Section width10.04"10.04"0.00"0.0%
Sidewall height6.02"7.03"+1.00"+16.7%
Circumference94.40"100.70"+6.31"+6.7%
Revolutions per mile671.2629.2−42.0−6.3%

Speedometer difference

If your vehicle came with 255/60R18 and you fit 255/70R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph32.0 mph+2.0 mph
40 mph42.7 mph+2.7 mph
50 mph53.3 mph+3.3 mph
60 mph64.0 mph+4.0 mph
65 mph69.3 mph+4.3 mph
70 mph74.7 mph+4.7 mph
75 mph80.0 mph+5.0 mph
80 mph85.3 mph+5.3 mph

Each size on its own

Questions

Which is bigger, 255/60R18 or 255/70R18?
255/70R18 is taller by 2.01 inches (32.06" vs 30.05"). 255/60R18 is the same width.
Can I replace 255/60R18 with 255/70R18?
It is not recommended without checking carefully. The diameter difference is +6.7%, 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 255/70R18 change my speedometer?
When your speedometer reads 60 mph with 255/70R18 fitted (calibrated for 255/60R18), your real speed is 64.0 mph. Your odometer will under-count miles by about 6.7%.
Will 255/70R18 lift my vehicle?
Ride height changes by half the diameter difference: +1.00 inches of ground clearance at the axle.

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