Tire Size Box

245/45R15 vs 245/55R15

245/55R15 compared with 245/45R15

+8.1% diameter, 0.0" width

245/55R15 is 25.61" tall vs 23.68". More than the 3% rule of thumb, so check carefully before switching.

23.7"15" rim4.3"9.6" wide
245/45R15 (solid) compared with 245/55R15 (dashed outline), drawn to scale

With 245/55R15 tires, when your speedometer says 60 mph you are really going

64.9 mph

245/55R15 is +1.93 inches (+8.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/45R15245/55R15Difference%
Overall diameter23.68"25.61"+1.93"+8.1%
Section width9.65"9.65"0.00"0.0%
Sidewall height4.34"5.31"+0.96"+22.2%
Circumference74.40"80.46"+6.06"+8.1%
Revolutions per mile851.7787.5−64.2−7.5%

Speedometer difference

If your vehicle came with 245/45R15 and you fit 245/55R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.6 mph+1.6 mph
30 mph32.4 mph+2.4 mph
40 mph43.3 mph+3.3 mph
50 mph54.1 mph+4.1 mph
60 mph64.9 mph+4.9 mph
65 mph70.3 mph+5.3 mph
70 mph75.7 mph+5.7 mph
75 mph81.1 mph+6.1 mph
80 mph86.5 mph+6.5 mph

Each size on its own

Questions

Which is bigger, 245/45R15 or 245/55R15?
245/55R15 is taller by 1.93 inches (25.61" vs 23.68"). 245/45R15 is the same width.
Can I replace 245/45R15 with 245/55R15?
It is not recommended without checking carefully. The diameter difference is +8.1%, 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 245/55R15 change my speedometer?
When your speedometer reads 60 mph with 245/55R15 fitted (calibrated for 245/45R15), your real speed is 64.9 mph. Your odometer will under-count miles by about 8.1%.
Will 245/55R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.96 inches of ground clearance at the axle.

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