Tire Size Box

325/40R19 vs 325/45R19

325/45R19 compared with 325/40R19

+4.4% diameter, 0.0" width

325/45R19 is 30.52" tall vs 29.24". More than the 3% rule of thumb, so check carefully before switching.

29.2"19" rim5.1"12.8" wide
325/40R19 (solid) compared with 325/45R19 (dashed outline), drawn to scale

With 325/45R19 tires, when your speedometer says 60 mph you are really going

62.6 mph

325/45R19 is +1.28 inches (+4.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

325/40R19325/45R19Difference%
Overall diameter29.24"30.52"+1.28"+4.4%
Section width12.80"12.80"0.00"0.0%
Sidewall height5.12"5.76"+0.64"+12.5%
Circumference91.85"95.87"+4.02"+4.4%
Revolutions per mile689.8660.9−28.9−4.2%

Speedometer difference

If your vehicle came with 325/40R19 and you fit 325/45R19, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.3 mph+1.3 mph
40 mph41.8 mph+1.8 mph
50 mph52.2 mph+2.2 mph
60 mph62.6 mph+2.6 mph
65 mph67.8 mph+2.8 mph
70 mph73.1 mph+3.1 mph
75 mph78.3 mph+3.3 mph
80 mph83.5 mph+3.5 mph

Each size on its own

Questions

Which is bigger, 325/40R19 or 325/45R19?
325/45R19 is taller by 1.28 inches (30.52" vs 29.24"). 325/40R19 is the same width.
Can I replace 325/40R19 with 325/45R19?
It is not recommended without checking carefully. The diameter difference is +4.4%, 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 325/45R19 change my speedometer?
When your speedometer reads 60 mph with 325/45R19 fitted (calibrated for 325/40R19), your real speed is 62.6 mph. Your odometer will under-count miles by about 4.4%.
Will 325/45R19 lift my vehicle?
Ride height changes by half the diameter difference: +0.64 inches of ground clearance at the axle.

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