Tire Size Box

325/30R19 vs 325/40R19

325/40R19 compared with 325/30R19

+9.6% diameter, 0.0" width

325/40R19 is 29.24" tall vs 26.68". More than the 3% rule of thumb, so check carefully before switching.

26.7"19" rim3.8"12.8" wide
325/30R19 (solid) compared with 325/40R19 (dashed outline), drawn to scale

With 325/40R19 tires, when your speedometer says 60 mph you are really going

65.8 mph

325/40R19 is +2.56 inches (+9.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

325/30R19325/40R19Difference%
Overall diameter26.68"29.24"+2.56"+9.6%
Section width12.80"12.80"0.00"0.0%
Sidewall height3.84"5.12"+1.28"+33.3%
Circumference83.81"91.85"+8.04"+9.6%
Revolutions per mile756.0689.8−66.2−8.8%

Speedometer difference

If your vehicle came with 325/30R19 and you fit 325/40R19, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.9 mph+1.9 mph
30 mph32.9 mph+2.9 mph
40 mph43.8 mph+3.8 mph
50 mph54.8 mph+4.8 mph
60 mph65.8 mph+5.8 mph
65 mph71.2 mph+6.2 mph
70 mph76.7 mph+6.7 mph
75 mph82.2 mph+7.2 mph
80 mph87.7 mph+7.7 mph

Each size on its own

Questions

Which is bigger, 325/30R19 or 325/40R19?
325/40R19 is taller by 2.56 inches (29.24" vs 26.68"). 325/30R19 is the same width.
Can I replace 325/30R19 with 325/40R19?
It is not recommended without checking carefully. The diameter difference is +9.6%, 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 325/40R19 change my speedometer?
When your speedometer reads 60 mph with 325/40R19 fitted (calibrated for 325/30R19), your real speed is 65.8 mph. Your odometer will under-count miles by about 9.6%.
Will 325/40R19 lift my vehicle?
Ride height changes by half the diameter difference: +1.28 inches of ground clearance at the axle.

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