Tire Size Box

315/30R24 vs 315/40R24

315/40R24 compared with 315/30R24

+7.9% diameter, 0.0" width

315/40R24 is 33.92" tall vs 31.44". More than the 3% rule of thumb, so check carefully before switching.

31.4"24" rim3.7"12.4" wide
315/30R24 (solid) compared with 315/40R24 (dashed outline), drawn to scale

With 315/40R24 tires, when your speedometer says 60 mph you are really going

64.7 mph

315/40R24 is +2.48 inches (+7.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/30R24315/40R24Difference%
Overall diameter31.44"33.92"+2.48"+7.9%
Section width12.40"12.40"0.00"0.0%
Sidewall height3.72"4.96"+1.24"+33.3%
Circumference98.77"106.57"+7.79"+7.9%
Revolutions per mile641.5594.6−46.9−7.3%

Speedometer difference

If your vehicle came with 315/30R24 and you fit 315/40R24, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.6 mph+1.6 mph
30 mph32.4 mph+2.4 mph
40 mph43.2 mph+3.2 mph
50 mph53.9 mph+3.9 mph
60 mph64.7 mph+4.7 mph
65 mph70.1 mph+5.1 mph
70 mph75.5 mph+5.5 mph
75 mph80.9 mph+5.9 mph
80 mph86.3 mph+6.3 mph

Each size on its own

Questions

Which is bigger, 315/30R24 or 315/40R24?
315/40R24 is taller by 2.48 inches (33.92" vs 31.44"). 315/30R24 is the same width.
Can I replace 315/30R24 with 315/40R24?
It is not recommended without checking carefully. The diameter difference is +7.9%, 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 315/40R24 change my speedometer?
When your speedometer reads 60 mph with 315/40R24 fitted (calibrated for 315/30R24), your real speed is 64.7 mph. Your odometer will under-count miles by about 7.9%.
Will 315/40R24 lift my vehicle?
Ride height changes by half the diameter difference: +1.24 inches of ground clearance at the axle.

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