Tire Size Box

355/30R19 vs 355/40R19

355/40R19 compared with 355/30R19

+10.2% diameter, 0.0" width

355/40R19 is 30.18" tall vs 27.39". More than the 3% rule of thumb, so check carefully before switching.

27.4"19" rim4.2"14.0" wide
355/30R19 (solid) compared with 355/40R19 (dashed outline), drawn to scale

With 355/40R19 tires, when your speedometer says 60 mph you are really going

66.1 mph

355/40R19 is +2.80 inches (+10.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

355/30R19355/40R19Difference%
Overall diameter27.39"30.18"+2.80"+10.2%
Section width13.98"13.98"0.00"0.0%
Sidewall height4.19"5.59"+1.40"+33.3%
Circumference86.04"94.82"+8.78"+10.2%
Revolutions per mile736.4668.2−68.2−9.3%

Speedometer difference

If your vehicle came with 355/30R19 and you fit 355/40R19, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph22.0 mph+2.0 mph
30 mph33.1 mph+3.1 mph
40 mph44.1 mph+4.1 mph
50 mph55.1 mph+5.1 mph
60 mph66.1 mph+6.1 mph
65 mph71.6 mph+6.6 mph
70 mph77.1 mph+7.1 mph
75 mph82.7 mph+7.7 mph
80 mph88.2 mph+8.2 mph

Each size on its own

Questions

Which is bigger, 355/30R19 or 355/40R19?
355/40R19 is taller by 2.80 inches (30.18" vs 27.39"). 355/30R19 is the same width.
Can I replace 355/30R19 with 355/40R19?
It is not recommended without checking carefully. The diameter difference is +10.2%, 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 355/40R19 change my speedometer?
When your speedometer reads 60 mph with 355/40R19 fitted (calibrated for 355/30R19), your real speed is 66.1 mph. Your odometer will under-count miles by about 10.2%.
Will 355/40R19 lift my vehicle?
Ride height changes by half the diameter difference: +1.40 inches of ground clearance at the axle.

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