Tire Size Box

225/45R20 vs 225/55R20

225/55R20 compared with 225/45R20

+6.3% diameter, 0.0" width

225/55R20 is 29.74" tall vs 27.97". More than the 3% rule of thumb, so check carefully before switching.

28.0"20" rim4.0"8.9" wide
225/45R20 (solid) compared with 225/55R20 (dashed outline), drawn to scale

With 225/55R20 tires, when your speedometer says 60 mph you are really going

63.8 mph

225/55R20 is +1.77 inches (+6.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

225/45R20225/55R20Difference%
Overall diameter27.97"29.74"+1.77"+6.3%
Section width8.86"8.86"0.00"0.0%
Sidewall height3.99"4.87"+0.89"+22.2%
Circumference87.88"93.44"+5.57"+6.3%
Revolutions per mile721.0678.1−42.9−6.0%

Speedometer difference

If your vehicle came with 225/45R20 and you fit 225/55R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph31.9 mph+1.9 mph
40 mph42.5 mph+2.5 mph
50 mph53.2 mph+3.2 mph
60 mph63.8 mph+3.8 mph
65 mph69.1 mph+4.1 mph
70 mph74.4 mph+4.4 mph
75 mph79.8 mph+4.8 mph
80 mph85.1 mph+5.1 mph

Each size on its own

Questions

Which is bigger, 225/45R20 or 225/55R20?
225/55R20 is taller by 1.77 inches (29.74" vs 27.97"). 225/45R20 is the same width.
Can I replace 225/45R20 with 225/55R20?
It is not recommended without checking carefully. The diameter difference is +6.3%, 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 225/55R20 change my speedometer?
When your speedometer reads 60 mph with 225/55R20 fitted (calibrated for 225/45R20), your real speed is 63.8 mph. Your odometer will under-count miles by about 6.3%.
Will 225/55R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.89 inches of ground clearance at the axle.

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