Tire Size Box

325/25R24 vs 315/30R24

315/30R24 compared with 325/25R24

+3.4% diameter, −0.4" width

315/30R24 is 31.44" tall vs 30.40". More than the 3% rule of thumb, so check carefully before switching.

30.4"24" rim3.2"12.8" wide
325/25R24 (solid) compared with 315/30R24 (dashed outline), drawn to scale

With 315/30R24 tires, when your speedometer says 60 mph you are really going

62.1 mph

315/30R24 is +1.04 inches (+3.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

325/25R24315/30R24Difference%
Overall diameter30.40"31.44"+1.04"+3.4%
Section width12.80"12.40"−0.39"−3.1%
Sidewall height3.20"3.72"+0.52"+16.3%
Circumference95.50"98.77"+3.28"+3.4%
Revolutions per mile663.5641.5−22.0−3.3%

Speedometer difference

If your vehicle came with 325/25R24 and you fit 315/30R24, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.4 mph+1.4 mph
50 mph51.7 mph+1.7 mph
60 mph62.1 mph+2.1 mph
65 mph67.2 mph+2.2 mph
70 mph72.4 mph+2.4 mph
75 mph77.6 mph+2.6 mph
80 mph82.7 mph+2.7 mph

Each size on its own

Questions

Which is bigger, 325/25R24 or 315/30R24?
315/30R24 is taller by 1.04 inches (31.44" vs 30.40"). 325/25R24 is wider by 0.39 inches.
Can I replace 325/25R24 with 315/30R24?
It is not recommended without checking carefully. The diameter difference is +3.4%, 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 315/30R24 change my speedometer?
When your speedometer reads 60 mph with 315/30R24 fitted (calibrated for 325/25R24), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.4%.
Will 315/30R24 lift my vehicle?
Ride height changes by half the diameter difference: +0.52 inches of ground clearance at the axle.

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