Tire Size Box

345/45R20 vs 345/50R20

345/50R20 compared with 345/45R20

+4.2% diameter, 0.0" width

345/50R20 is 33.58" tall vs 32.22". More than the 3% rule of thumb, so check carefully before switching.

32.2"20" rim6.1"13.6" wide
345/45R20 (solid) compared with 345/50R20 (dashed outline), drawn to scale

With 345/50R20 tires, when your speedometer says 60 mph you are really going

62.5 mph

345/50R20 is +1.36 inches (+4.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

345/45R20345/50R20Difference%
Overall diameter32.22"33.58"+1.36"+4.2%
Section width13.58"13.58"0.00"0.0%
Sidewall height6.11"6.79"+0.68"+11.1%
Circumference101.24"105.50"+4.27"+4.2%
Revolutions per mile625.9600.6−25.3−4.0%

Speedometer difference

If your vehicle came with 345/45R20 and you fit 345/50R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.3 mph+1.3 mph
40 mph41.7 mph+1.7 mph
50 mph52.1 mph+2.1 mph
60 mph62.5 mph+2.5 mph
65 mph67.7 mph+2.7 mph
70 mph73.0 mph+3.0 mph
75 mph78.2 mph+3.2 mph
80 mph83.4 mph+3.4 mph

Each size on its own

Questions

Which is bigger, 345/45R20 or 345/50R20?
345/50R20 is taller by 1.36 inches (33.58" vs 32.22"). 345/45R20 is the same width.
Can I replace 345/45R20 with 345/50R20?
It is not recommended without checking carefully. The diameter difference is +4.2%, 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 345/50R20 change my speedometer?
When your speedometer reads 60 mph with 345/50R20 fitted (calibrated for 345/45R20), your real speed is 62.5 mph. Your odometer will under-count miles by about 4.2%.
Will 345/50R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.68 inches of ground clearance at the axle.

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