Tire Size Box

345/40R19 vs 345/45R19

345/45R19 compared with 345/40R19

+4.5% diameter, 0.0" width

345/45R19 is 31.22" tall vs 29.87". More than the 3% rule of thumb, so check carefully before switching.

29.9"19" rim5.4"13.6" wide
345/40R19 (solid) compared with 345/45R19 (dashed outline), drawn to scale

With 345/45R19 tires, when your speedometer says 60 mph you are really going

62.7 mph

345/45R19 is +1.36 inches (+4.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

345/40R19345/45R19Difference%
Overall diameter29.87"31.22"+1.36"+4.5%
Section width13.58"13.58"0.00"0.0%
Sidewall height5.43"6.11"+0.68"+12.5%
Circumference93.83"98.09"+4.27"+4.5%
Revolutions per mile675.3645.9−29.4−4.4%

Speedometer difference

If your vehicle came with 345/40R19 and you fit 345/45R19, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.4 mph+1.4 mph
40 mph41.8 mph+1.8 mph
50 mph52.3 mph+2.3 mph
60 mph62.7 mph+2.7 mph
65 mph68.0 mph+3.0 mph
70 mph73.2 mph+3.2 mph
75 mph78.4 mph+3.4 mph
80 mph83.6 mph+3.6 mph

Each size on its own

Questions

Which is bigger, 345/40R19 or 345/45R19?
345/45R19 is taller by 1.36 inches (31.22" vs 29.87"). 345/40R19 is the same width.
Can I replace 345/40R19 with 345/45R19?
It is not recommended without checking carefully. The diameter difference is +4.5%, 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 345/45R19 change my speedometer?
When your speedometer reads 60 mph with 345/45R19 fitted (calibrated for 345/40R19), your real speed is 62.7 mph. Your odometer will under-count miles by about 4.5%.
Will 345/45R19 lift my vehicle?
Ride height changes by half the diameter difference: +0.68 inches of ground clearance at the axle.

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