Tire Size Box

325/45R20 vs 325/50R20

325/50R20 compared with 325/45R20

+4.1% diameter, 0.0" width

325/50R20 is 32.80" tall vs 31.52". More than the 3% rule of thumb, so check carefully before switching.

31.5"20" rim5.8"12.8" wide
325/45R20 (solid) compared with 325/50R20 (dashed outline), drawn to scale

With 325/50R20 tires, when your speedometer says 60 mph you are really going

62.4 mph

325/50R20 is +1.28 inches (+4.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

325/45R20325/50R20Difference%
Overall diameter31.52"32.80"+1.28"+4.1%
Section width12.80"12.80"0.00"0.0%
Sidewall height5.76"6.40"+0.64"+11.1%
Circumference99.01"103.03"+4.02"+4.1%
Revolutions per mile639.9615.0−25.0−3.9%

Speedometer difference

If your vehicle came with 325/45R20 and you fit 325/50R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.6 mph+1.6 mph
50 mph52.0 mph+2.0 mph
60 mph62.4 mph+2.4 mph
65 mph67.6 mph+2.6 mph
70 mph72.8 mph+2.8 mph
75 mph78.0 mph+3.0 mph
80 mph83.2 mph+3.2 mph

Each size on its own

Questions

Which is bigger, 325/45R20 or 325/50R20?
325/50R20 is taller by 1.28 inches (32.80" vs 31.52"). 325/45R20 is the same width.
Can I replace 325/45R20 with 325/50R20?
It is not recommended without checking carefully. The diameter difference is +4.1%, 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 325/50R20 change my speedometer?
When your speedometer reads 60 mph with 325/50R20 fitted (calibrated for 325/45R20), your real speed is 62.4 mph. Your odometer will under-count miles by about 4.1%.
Will 325/50R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.64 inches of ground clearance at the axle.

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