Tire Size Box

315/30R19 vs 315/40R19

315/40R19 compared with 315/30R19

+9.4% diameter, 0.0" width

315/40R19 is 28.92" tall vs 26.44". More than the 3% rule of thumb, so check carefully before switching.

26.4"19" rim3.7"12.4" wide
315/30R19 (solid) compared with 315/40R19 (dashed outline), drawn to scale

With 315/40R19 tires, when your speedometer says 60 mph you are really going

65.6 mph

315/40R19 is +2.48 inches (+9.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/30R19315/40R19Difference%
Overall diameter26.44"28.92"+2.48"+9.4%
Section width12.40"12.40"0.00"0.0%
Sidewall height3.72"4.96"+1.24"+33.3%
Circumference83.07"90.86"+7.79"+9.4%
Revolutions per mile762.8697.3−65.4−8.6%

Speedometer difference

If your vehicle came with 315/30R19 and you fit 315/40R19, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.9 mph+1.9 mph
30 mph32.8 mph+2.8 mph
40 mph43.8 mph+3.8 mph
50 mph54.7 mph+4.7 mph
60 mph65.6 mph+5.6 mph
65 mph71.1 mph+6.1 mph
70 mph76.6 mph+6.6 mph
75 mph82.0 mph+7.0 mph
80 mph87.5 mph+7.5 mph

Each size on its own

Questions

Which is bigger, 315/30R19 or 315/40R19?
315/40R19 is taller by 2.48 inches (28.92" vs 26.44"). 315/30R19 is the same width.
Can I replace 315/30R19 with 315/40R19?
It is not recommended without checking carefully. The diameter difference is +9.4%, 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 315/40R19 change my speedometer?
When your speedometer reads 60 mph with 315/40R19 fitted (calibrated for 315/30R19), your real speed is 65.6 mph. Your odometer will under-count miles by about 9.4%.
Will 315/40R19 lift my vehicle?
Ride height changes by half the diameter difference: +1.24 inches of ground clearance at the axle.

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