Tire Size Box

315/60R18 vs 315/70R18

315/70R18 compared with 315/60R18

+7.5% diameter, 0.0" width

315/70R18 is 35.36" tall vs 32.88". More than the 3% rule of thumb, so check carefully before switching.

32.9"18" rim7.4"12.4" wide
315/60R18 (solid) compared with 315/70R18 (dashed outline), drawn to scale

With 315/70R18 tires, when your speedometer says 60 mph you are really going

64.5 mph

315/70R18 is +2.48 inches (+7.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/60R18315/70R18Difference%
Overall diameter32.88"35.36"+2.48"+7.5%
Section width12.40"12.40"0.00"0.0%
Sidewall height7.44"8.68"+1.24"+16.7%
Circumference103.30"111.09"+7.79"+7.5%
Revolutions per mile613.4570.3−43.0−7.0%

Speedometer difference

If your vehicle came with 315/60R18 and you fit 315/70R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.5 mph+1.5 mph
30 mph32.3 mph+2.3 mph
40 mph43.0 mph+3.0 mph
50 mph53.8 mph+3.8 mph
60 mph64.5 mph+4.5 mph
65 mph69.9 mph+4.9 mph
70 mph75.3 mph+5.3 mph
75 mph80.7 mph+5.7 mph
80 mph86.0 mph+6.0 mph

Each size on its own

Questions

Which is bigger, 315/60R18 or 315/70R18?
315/70R18 is taller by 2.48 inches (35.36" vs 32.88"). 315/60R18 is the same width.
Can I replace 315/60R18 with 315/70R18?
It is not recommended without checking carefully. The diameter difference is +7.5%, 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 315/70R18 change my speedometer?
When your speedometer reads 60 mph with 315/70R18 fitted (calibrated for 315/60R18), your real speed is 64.5 mph. Your odometer will under-count miles by about 7.5%.
Will 315/70R18 lift my vehicle?
Ride height changes by half the diameter difference: +1.24 inches of ground clearance at the axle.

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