Tire Size Box

245/45R21 vs 245/55R21

245/55R21 compared with 245/45R21

+6.5% diameter, 0.0" width

245/55R21 is 31.61" tall vs 29.68". More than the 3% rule of thumb, so check carefully before switching.

29.7"21" rim4.3"9.6" wide
245/45R21 (solid) compared with 245/55R21 (dashed outline), drawn to scale

With 245/55R21 tires, when your speedometer says 60 mph you are really going

63.9 mph

245/55R21 is +1.93 inches (+6.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/45R21245/55R21Difference%
Overall diameter29.68"31.61"+1.93"+6.5%
Section width9.65"9.65"0.00"0.0%
Sidewall height4.34"5.31"+0.96"+22.2%
Circumference93.25"99.31"+6.06"+6.5%
Revolutions per mile679.5638.0−41.5−6.1%

Speedometer difference

If your vehicle came with 245/45R21 and you fit 245/55R21, 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 mph42.6 mph+2.6 mph
50 mph53.2 mph+3.2 mph
60 mph63.9 mph+3.9 mph
65 mph69.2 mph+4.2 mph
70 mph74.5 mph+4.5 mph
75 mph79.9 mph+4.9 mph
80 mph85.2 mph+5.2 mph

Each size on its own

Questions

Which is bigger, 245/45R21 or 245/55R21?
245/55R21 is taller by 1.93 inches (31.61" vs 29.68"). 245/45R21 is the same width.
Can I replace 245/45R21 with 245/55R21?
It is not recommended without checking carefully. The diameter difference is +6.5%, 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 245/55R21 change my speedometer?
When your speedometer reads 60 mph with 245/55R21 fitted (calibrated for 245/45R21), your real speed is 63.9 mph. Your odometer will under-count miles by about 6.5%.
Will 245/55R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.96 inches of ground clearance at the axle.

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