Tire Size Box

325/50R20 vs 325/55R20

325/55R20 compared with 325/50R20

+3.9% diameter, 0.0" width

325/55R20 is 34.07" tall vs 32.80". More than the 3% rule of thumb, so check carefully before switching.

32.8"20" rim6.4"12.8" wide
325/50R20 (solid) compared with 325/55R20 (dashed outline), drawn to scale

With 325/55R20 tires, when your speedometer says 60 mph you are really going

62.3 mph

325/55R20 is +1.28 inches (+3.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

325/50R20325/55R20Difference%
Overall diameter32.80"34.07"+1.28"+3.9%
Section width12.80"12.80"0.00"0.0%
Sidewall height6.40"7.04"+0.64"+10.0%
Circumference103.03"107.05"+4.02"+3.9%
Revolutions per mile615.0591.9−23.1−3.8%

Speedometer difference

If your vehicle came with 325/50R20 and you fit 325/55R20, 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 mph62.3 mph+2.3 mph
65 mph67.5 mph+2.5 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, 325/50R20 or 325/55R20?
325/55R20 is taller by 1.28 inches (34.07" vs 32.80"). 325/50R20 is the same width.
Can I replace 325/50R20 with 325/55R20?
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 325/55R20 change my speedometer?
When your speedometer reads 60 mph with 325/55R20 fitted (calibrated for 325/50R20), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.9%.
Will 325/55R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.64 inches of ground clearance at the axle.

Other comparisons