Tire Size Box

355/45R21 vs 355/50R21

355/50R21 compared with 355/45R21

+4.2% diameter, 0.0" width

355/50R21 is 34.98" tall vs 33.58". More than the 3% rule of thumb, so check carefully before switching.

33.6"21" rim6.3"14.0" wide
355/45R21 (solid) compared with 355/50R21 (dashed outline), drawn to scale

With 355/50R21 tires, when your speedometer says 60 mph you are really going

62.5 mph

355/50R21 is +1.40 inches (+4.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

355/45R21355/50R21Difference%
Overall diameter33.58"34.98"+1.40"+4.2%
Section width13.98"13.98"0.00"0.0%
Sidewall height6.29"6.99"+0.70"+11.1%
Circumference105.49"109.88"+4.39"+4.2%
Revolutions per mile600.6576.6−24.0−4.0%

Speedometer difference

If your vehicle came with 355/45R21 and you fit 355/50R21, 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 mph41.7 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 mph72.9 mph+2.9 mph
75 mph78.1 mph+3.1 mph
80 mph83.3 mph+3.3 mph

Each size on its own

Questions

Which is bigger, 355/45R21 or 355/50R21?
355/50R21 is taller by 1.40 inches (34.98" vs 33.58"). 355/45R21 is the same width.
Can I replace 355/45R21 with 355/50R21?
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 355/50R21 change my speedometer?
When your speedometer reads 60 mph with 355/50R21 fitted (calibrated for 355/45R21), your real speed is 62.5 mph. Your odometer will under-count miles by about 4.2%.
Will 355/50R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.70 inches of ground clearance at the axle.

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