Tire Size Box

225/45R21 vs 225/55R21

225/55R21 compared with 225/45R21

+6.1% diameter, 0.0" width

225/55R21 is 30.74" tall vs 28.97". More than the 3% rule of thumb, so check carefully before switching.

29.0"21" rim4.0"8.9" wide
225/45R21 (solid) compared with 225/55R21 (dashed outline), drawn to scale

With 225/55R21 tires, when your speedometer says 60 mph you are really going

63.7 mph

225/55R21 is +1.77 inches (+6.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

225/45R21225/55R21Difference%
Overall diameter28.97"30.74"+1.77"+6.1%
Section width8.86"8.86"0.00"0.0%
Sidewall height3.99"4.87"+0.89"+22.2%
Circumference91.02"96.59"+5.57"+6.1%
Revolutions per mile696.1656.0−40.1−5.8%

Speedometer difference

If your vehicle came with 225/45R21 and you fit 225/55R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.2 mph+1.2 mph
30 mph31.8 mph+1.8 mph
40 mph42.4 mph+2.4 mph
50 mph53.1 mph+3.1 mph
60 mph63.7 mph+3.7 mph
65 mph69.0 mph+4.0 mph
70 mph74.3 mph+4.3 mph
75 mph79.6 mph+4.6 mph
80 mph84.9 mph+4.9 mph

Each size on its own

Questions

Which is bigger, 225/45R21 or 225/55R21?
225/55R21 is taller by 1.77 inches (30.74" vs 28.97"). 225/45R21 is the same width.
Can I replace 225/45R21 with 225/55R21?
It is not recommended without checking carefully. The diameter difference is +6.1%, 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 225/55R21 change my speedometer?
When your speedometer reads 60 mph with 225/55R21 fitted (calibrated for 225/45R21), your real speed is 63.7 mph. Your odometer will under-count miles by about 6.1%.
Will 225/55R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.89 inches of ground clearance at the axle.

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