Tire Size Box

295/65R18 vs 315/65R18

315/65R18 compared with 295/65R18

+3.1% diameter, +0.8" width

315/65R18 is 34.12" tall vs 33.10". More than the 3% rule of thumb, so check carefully before switching.

33.1"18" rim7.5"11.6" wide
295/65R18 (solid) compared with 315/65R18 (dashed outline), drawn to scale

With 315/65R18 tires, when your speedometer says 60 mph you are really going

61.9 mph

315/65R18 is +1.02 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

295/65R18315/65R18Difference%
Overall diameter33.10"34.12"+1.02"+3.1%
Section width11.61"12.40"+0.79"+6.8%
Sidewall height7.55"8.06"+0.51"+6.8%
Circumference103.98"107.20"+3.22"+3.1%
Revolutions per mile609.3591.1−18.3−3.0%

Speedometer difference

If your vehicle came with 295/65R18 and you fit 315/65R18, 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 mph41.2 mph+1.2 mph
50 mph51.5 mph+1.5 mph
60 mph61.9 mph+1.9 mph
65 mph67.0 mph+2.0 mph
70 mph72.2 mph+2.2 mph
75 mph77.3 mph+2.3 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 295/65R18 or 315/65R18?
315/65R18 is taller by 1.02 inches (34.12" vs 33.10"). 315/65R18 is wider by 0.79 inches.
Can I replace 295/65R18 with 315/65R18?
It is not recommended without checking carefully. The diameter difference is +3.1%, 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 315/65R18 change my speedometer?
When your speedometer reads 60 mph with 315/65R18 fitted (calibrated for 295/65R18), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.1%.
Will 315/65R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.51 inches of ground clearance at the axle.

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