Tire Size Box

315/70R17 vs 315/75R17

315/75R17 compared with 315/70R17

+3.6% diameter, 0.0" width

315/75R17 is 35.60" tall vs 34.36". More than the 3% rule of thumb, so check carefully before switching.

34.4"17" rim8.7"12.4" wide
315/70R17 (solid) compared with 315/75R17 (dashed outline), drawn to scale

With 315/75R17 tires, when your speedometer says 60 mph you are really going

62.2 mph

315/75R17 is +1.24 inches (+3.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/70R17315/75R17Difference%
Overall diameter34.36"35.60"+1.24"+3.6%
Section width12.40"12.40"0.00"0.0%
Sidewall height8.68"9.30"+0.62"+7.1%
Circumference107.95"111.85"+3.90"+3.6%
Revolutions per mile586.9566.5−20.4−3.5%

Speedometer difference

If your vehicle came with 315/70R17 and you fit 315/75R17, 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 mph62.2 mph+2.2 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, 315/70R17 or 315/75R17?
315/75R17 is taller by 1.24 inches (35.60" vs 34.36"). 315/70R17 is the same width.
Can I replace 315/70R17 with 315/75R17?
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 315/75R17 change my speedometer?
When your speedometer reads 60 mph with 315/75R17 fitted (calibrated for 315/70R17), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.6%.
Will 315/75R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.62 inches of ground clearance at the axle.

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