Tire Size Box

275/45R21 vs 275/55R21

275/55R21 compared with 275/45R21

+7.0% diameter, 0.0" width

275/55R21 is 32.91" tall vs 30.74". More than the 3% rule of thumb, so check carefully before switching.

30.7"21" rim4.9"10.8" wide
275/45R21 (solid) compared with 275/55R21 (dashed outline), drawn to scale

With 275/55R21 tires, when your speedometer says 60 mph you are really going

64.2 mph

275/55R21 is +2.17 inches (+7.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

275/45R21275/55R21Difference%
Overall diameter30.74"32.91"+2.17"+7.0%
Section width10.83"10.83"0.00"0.0%
Sidewall height4.87"5.95"+1.08"+22.2%
Circumference96.59"103.39"+6.80"+7.0%
Revolutions per mile656.0612.8−43.2−6.6%

Speedometer difference

If your vehicle came with 275/45R21 and you fit 275/55R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.4 mph+1.4 mph
30 mph32.1 mph+2.1 mph
40 mph42.8 mph+2.8 mph
50 mph53.5 mph+3.5 mph
60 mph64.2 mph+4.2 mph
65 mph69.6 mph+4.6 mph
70 mph74.9 mph+4.9 mph
75 mph80.3 mph+5.3 mph
80 mph85.6 mph+5.6 mph

Each size on its own

Questions

Which is bigger, 275/45R21 or 275/55R21?
275/55R21 is taller by 2.17 inches (32.91" vs 30.74"). 275/45R21 is the same width.
Can I replace 275/45R21 with 275/55R21?
It is not recommended without checking carefully. The diameter difference is +7.0%, 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 275/55R21 change my speedometer?
When your speedometer reads 60 mph with 275/55R21 fitted (calibrated for 275/45R21), your real speed is 64.2 mph. Your odometer will under-count miles by about 7.0%.
Will 275/55R21 lift my vehicle?
Ride height changes by half the diameter difference: +1.08 inches of ground clearance at the axle.

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