Tire Size Box

345/50R21 vs 345/55R21

345/55R21 compared with 345/50R21

+3.9% diameter, 0.0" width

345/55R21 is 35.94" tall vs 34.58". More than the 3% rule of thumb, so check carefully before switching.

34.6"21" rim6.8"13.6" wide
345/50R21 (solid) compared with 345/55R21 (dashed outline), drawn to scale

With 345/55R21 tires, when your speedometer says 60 mph you are really going

62.4 mph

345/55R21 is +1.36 inches (+3.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

345/50R21345/55R21Difference%
Overall diameter34.58"35.94"+1.36"+3.9%
Section width13.58"13.58"0.00"0.0%
Sidewall height6.79"7.47"+0.68"+10.0%
Circumference108.64"112.91"+4.27"+3.9%
Revolutions per mile583.2561.1−22.0−3.8%

Speedometer difference

If your vehicle came with 345/50R21 and you fit 345/55R21, 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 mph72.7 mph+2.7 mph
75 mph77.9 mph+2.9 mph
80 mph83.1 mph+3.1 mph

Each size on its own

Questions

Which is bigger, 345/50R21 or 345/55R21?
345/55R21 is taller by 1.36 inches (35.94" vs 34.58"). 345/50R21 is the same width.
Can I replace 345/50R21 with 345/55R21?
It is not recommended without checking carefully. The diameter difference is +3.9%, 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 345/55R21 change my speedometer?
When your speedometer reads 60 mph with 345/55R21 fitted (calibrated for 345/50R21), your real speed is 62.4 mph. Your odometer will under-count miles by about 3.9%.
Will 345/55R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.68 inches of ground clearance at the axle.

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