Tire Size Box

345/30R19 vs 345/40R19

345/40R19 compared with 345/30R19

+10.0% diameter, 0.0" width

345/40R19 is 29.87" tall vs 27.15". More than the 3% rule of thumb, so check carefully before switching.

27.1"19" rim4.1"13.6" wide
345/30R19 (solid) compared with 345/40R19 (dashed outline), drawn to scale

With 345/40R19 tires, when your speedometer says 60 mph you are really going

66.0 mph

345/40R19 is +2.72 inches (+10.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

345/30R19345/40R19Difference%
Overall diameter27.15"29.87"+2.72"+10.0%
Section width13.58"13.58"0.00"0.0%
Sidewall height4.07"5.43"+1.36"+33.3%
Circumference85.29"93.83"+8.53"+10.0%
Revolutions per mile742.9675.3−67.6−9.1%

Speedometer difference

If your vehicle came with 345/30R19 and you fit 345/40R19, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph22.0 mph+2.0 mph
30 mph33.0 mph+3.0 mph
40 mph44.0 mph+4.0 mph
50 mph55.0 mph+5.0 mph
60 mph66.0 mph+6.0 mph
65 mph71.5 mph+6.5 mph
70 mph77.0 mph+7.0 mph
75 mph82.5 mph+7.5 mph
80 mph88.0 mph+8.0 mph

Each size on its own

Questions

Which is bigger, 345/30R19 or 345/40R19?
345/40R19 is taller by 2.72 inches (29.87" vs 27.15"). 345/30R19 is the same width.
Can I replace 345/30R19 with 345/40R19?
It is not recommended without checking carefully. The diameter difference is +10.0%, 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 345/40R19 change my speedometer?
When your speedometer reads 60 mph with 345/40R19 fitted (calibrated for 345/30R19), your real speed is 66.0 mph. Your odometer will under-count miles by about 10.0%.
Will 345/40R19 lift my vehicle?
Ride height changes by half the diameter difference: +1.36 inches of ground clearance at the axle.

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