Tire Size Box

315/35R19 vs 305/40R19

305/40R19 compared with 315/35R19

+3.3% diameter, −0.4" width

305/40R19 is 28.61" tall vs 27.68". More than the 3% rule of thumb, so check carefully before switching.

27.7"19" rim4.3"12.4" wide
315/35R19 (solid) compared with 305/40R19 (dashed outline), drawn to scale

With 305/40R19 tires, when your speedometer says 60 mph you are really going

62.0 mph

305/40R19 is +0.93 inches (+3.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/35R19305/40R19Difference%
Overall diameter27.68"28.61"+0.93"+3.3%
Section width12.40"12.01"−0.39"−3.2%
Sidewall height4.34"4.80"+0.46"+10.7%
Circumference86.96"89.87"+2.91"+3.3%
Revolutions per mile728.6705.0−23.6−3.2%

Speedometer difference

If your vehicle came with 315/35R19 and you fit 305/40R19, 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 mph41.3 mph+1.3 mph
50 mph51.7 mph+1.7 mph
60 mph62.0 mph+2.0 mph
65 mph67.2 mph+2.2 mph
70 mph72.3 mph+2.3 mph
75 mph77.5 mph+2.5 mph
80 mph82.7 mph+2.7 mph

Each size on its own

Questions

Which is bigger, 315/35R19 or 305/40R19?
305/40R19 is taller by 0.93 inches (28.61" vs 27.68"). 315/35R19 is wider by 0.39 inches.
Can I replace 315/35R19 with 305/40R19?
It is not recommended without checking carefully. The diameter difference is +3.3%, 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 305/40R19 change my speedometer?
When your speedometer reads 60 mph with 305/40R19 fitted (calibrated for 315/35R19), your real speed is 62.0 mph. Your odometer will under-count miles by about 3.3%.
Will 305/40R19 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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