Tire Size Box

255/65R15 vs 255/70R15

255/70R15 compared with 255/65R15

+3.6% diameter, 0.0" width

255/70R15 is 29.06" tall vs 28.05". More than the 3% rule of thumb, so check carefully before switching.

28.1"15" rim6.5"10.0" wide
255/65R15 (solid) compared with 255/70R15 (dashed outline), drawn to scale

With 255/70R15 tires, when your speedometer says 60 mph you are really going

62.1 mph

255/70R15 is +1.00 inches (+3.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/65R15255/70R15Difference%
Overall diameter28.05"29.06"+1.00"+3.6%
Section width10.04"10.04"0.00"0.0%
Sidewall height6.53"7.03"+0.50"+7.7%
Circumference88.13"91.28"+3.15"+3.6%
Revolutions per mile719.0694.1−24.8−3.5%

Speedometer difference

If your vehicle came with 255/65R15 and you fit 255/70R15, 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 mph77.7 mph+2.7 mph
80 mph82.9 mph+2.9 mph

Each size on its own

Questions

Which is bigger, 255/65R15 or 255/70R15?
255/70R15 is taller by 1.00 inches (29.06" vs 28.05"). 255/65R15 is the same width.
Can I replace 255/65R15 with 255/70R15?
It is not recommended without checking carefully. The diameter difference is +3.6%, 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 255/70R15 change my speedometer?
When your speedometer reads 60 mph with 255/70R15 fitted (calibrated for 255/65R15), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.6%.
Will 255/70R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.50 inches of ground clearance at the axle.

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