Tire Size Box

295/70R18 vs 315/70R18

315/70R18 compared with 295/70R18

+3.2% diameter, +0.8" width

315/70R18 is 35.36" tall vs 34.26". More than the 3% rule of thumb, so check carefully before switching.

34.3"18" rim8.1"11.6" wide
295/70R18 (solid) compared with 315/70R18 (dashed outline), drawn to scale

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

61.9 mph

315/70R18 is +1.10 inches (+3.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

295/70R18315/70R18Difference%
Overall diameter34.26"35.36"+1.10"+3.2%
Section width11.61"12.40"+0.79"+6.8%
Sidewall height8.13"8.68"+0.55"+6.8%
Circumference107.63"111.09"+3.46"+3.2%
Revolutions per mile588.7570.3−18.4−3.1%

Speedometer difference

If your vehicle came with 295/70R18 and you fit 315/70R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph31.0 mph+1.0 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 mph72.3 mph+2.3 mph
75 mph77.4 mph+2.4 mph
80 mph82.6 mph+2.6 mph

Each size on its own

Questions

Which is bigger, 295/70R18 or 315/70R18?
315/70R18 is taller by 1.10 inches (35.36" vs 34.26"). 315/70R18 is wider by 0.79 inches.
Can I replace 295/70R18 with 315/70R18?
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 315/70R18 change my speedometer?
When your speedometer reads 60 mph with 315/70R18 fitted (calibrated for 295/70R18), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.2%.
Will 315/70R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.55 inches of ground clearance at the axle.

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