Tire Size Box

325/40R19 vs 315/45R19

315/45R19 compared with 325/40R19

+3.2% diameter, −0.4" width

315/45R19 is 30.16" tall vs 29.24". More than the 3% rule of thumb, so check carefully before switching.

29.2"19" rim5.1"12.8" wide
325/40R19 (solid) compared with 315/45R19 (dashed outline), drawn to scale

With 315/45R19 tires, when your speedometer says 60 mph you are really going

61.9 mph

315/45R19 is +0.93 inches (+3.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

325/40R19315/45R19Difference%
Overall diameter29.24"30.16"+0.93"+3.2%
Section width12.80"12.40"−0.39"−3.1%
Sidewall height5.12"5.58"+0.46"+9.0%
Circumference91.85"94.75"+2.91"+3.2%
Revolutions per mile689.8668.7−21.2−3.1%

Speedometer difference

If your vehicle came with 325/40R19 and you fit 315/45R19, 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 mph41.3 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 mph72.2 mph+2.2 mph
75 mph77.4 mph+2.4 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 325/40R19 or 315/45R19?
315/45R19 is taller by 0.93 inches (30.16" vs 29.24"). 325/40R19 is wider by 0.39 inches.
Can I replace 325/40R19 with 315/45R19?
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 315/45R19 change my speedometer?
When your speedometer reads 60 mph with 315/45R19 fitted (calibrated for 325/40R19), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.2%.
Will 315/45R19 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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