Tire Size Box

345/50R20 vs 345/55R20

345/55R20 compared with 345/50R20

+4.0% diameter, 0.0" width

345/55R20 is 34.94" tall vs 33.58". More than the 3% rule of thumb, so check carefully before switching.

33.6"20" rim6.8"13.6" wide
345/50R20 (solid) compared with 345/55R20 (dashed outline), drawn to scale

With 345/55R20 tires, when your speedometer says 60 mph you are really going

62.4 mph

345/55R20 is +1.36 inches (+4.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

345/50R20345/55R20Difference%
Overall diameter33.58"34.94"+1.36"+4.0%
Section width13.58"13.58"0.00"0.0%
Sidewall height6.79"7.47"+0.68"+10.0%
Circumference105.50"109.77"+4.27"+4.0%
Revolutions per mile600.6577.2−23.3−3.9%

Speedometer difference

If your vehicle came with 345/50R20 and you fit 345/55R20, 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, 345/50R20 or 345/55R20?
345/55R20 is taller by 1.36 inches (34.94" vs 33.58"). 345/50R20 is the same width.
Can I replace 345/50R20 with 345/55R20?
It is not recommended without checking carefully. The diameter difference is +4.0%, 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 345/55R20 change my speedometer?
When your speedometer reads 60 mph with 345/55R20 fitted (calibrated for 345/50R20), your real speed is 62.4 mph. Your odometer will under-count miles by about 4.0%.
Will 345/55R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.68 inches of ground clearance at the axle.

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