Tire Size Box

245/65R18 vs 245/70R18

245/70R18 compared with 245/65R18

+3.2% diameter, 0.0" width

245/70R18 is 31.50" tall vs 30.54". More than the 3% rule of thumb, so check carefully before switching.

30.5"18" rim6.3"9.6" wide
245/65R18 (solid) compared with 245/70R18 (dashed outline), drawn to scale

With 245/70R18 tires, when your speedometer says 60 mph you are really going

61.9 mph

245/70R18 is +0.96 inches (+3.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/65R18245/70R18Difference%
Overall diameter30.54"31.50"+0.96"+3.2%
Section width9.65"9.65"0.00"0.0%
Sidewall height6.27"6.75"+0.48"+7.7%
Circumference95.94"98.97"+3.03"+3.2%
Revolutions per mile660.4640.2−20.2−3.1%

Speedometer difference

If your vehicle came with 245/65R18 and you fit 245/70R18, 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 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.1 mph+2.1 mph
70 mph72.2 mph+2.2 mph
75 mph77.4 mph+2.4 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 245/65R18 or 245/70R18?
245/70R18 is taller by 0.96 inches (31.50" vs 30.54"). 245/65R18 is the same width.
Can I replace 245/65R18 with 245/70R18?
It is not recommended without checking carefully. The diameter difference is +3.2%, 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 245/70R18 change my speedometer?
When your speedometer reads 60 mph with 245/70R18 fitted (calibrated for 245/65R18), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.2%.
Will 245/70R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.48 inches of ground clearance at the axle.

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