Tire Size Box

245/60R18 vs 245/70R18

245/70R18 compared with 245/60R18

+6.5% diameter, 0.0" width

245/70R18 is 31.50" tall vs 29.57". More than the 3% rule of thumb, so check carefully before switching.

29.6"18" rim5.8"9.6" wide
245/60R18 (solid) compared with 245/70R18 (dashed outline), drawn to scale

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

63.9 mph

245/70R18 is +1.93 inches (+6.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/60R18245/70R18Difference%
Overall diameter29.57"31.50"+1.93"+6.5%
Section width9.65"9.65"0.00"0.0%
Sidewall height5.79"6.75"+0.96"+16.7%
Circumference92.91"98.97"+6.06"+6.5%
Revolutions per mile681.9640.2−41.8−6.1%

Speedometer difference

If your vehicle came with 245/60R18 and you fit 245/70R18, 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 mph42.6 mph+2.6 mph
50 mph53.3 mph+3.3 mph
60 mph63.9 mph+3.9 mph
65 mph69.2 mph+4.2 mph
70 mph74.6 mph+4.6 mph
75 mph79.9 mph+4.9 mph
80 mph85.2 mph+5.2 mph

Each size on its own

Questions

Which is bigger, 245/60R18 or 245/70R18?
245/70R18 is taller by 1.93 inches (31.50" vs 29.57"). 245/60R18 is the same width.
Can I replace 245/60R18 with 245/70R18?
It is not recommended without checking carefully. The diameter difference is +6.5%, 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 245/60R18), your real speed is 63.9 mph. Your odometer will under-count miles by about 6.5%.
Will 245/70R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.96 inches of ground clearance at the axle.

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