Tire Size Box

245/50R18 vs 245/55R18

245/55R18 compared with 245/50R18

+3.5% diameter, 0.0" width

245/55R18 is 28.61" tall vs 27.65". More than the 3% rule of thumb, so check carefully before switching.

27.6"18" rim4.8"9.6" wide
245/50R18 (solid) compared with 245/55R18 (dashed outline), drawn to scale

With 245/55R18 tires, when your speedometer says 60 mph you are really going

62.1 mph

245/55R18 is +0.96 inches (+3.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/50R18245/55R18Difference%
Overall diameter27.65"28.61"+0.96"+3.5%
Section width9.65"9.65"0.00"0.0%
Sidewall height4.82"5.31"+0.48"+10.0%
Circumference86.85"89.88"+3.03"+3.5%
Revolutions per mile729.5704.9−24.6−3.4%

Speedometer difference

If your vehicle came with 245/50R18 and you fit 245/55R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.4 mph+1.4 mph
50 mph51.7 mph+1.7 mph
60 mph62.1 mph+2.1 mph
65 mph67.3 mph+2.3 mph
70 mph72.4 mph+2.4 mph
75 mph77.6 mph+2.6 mph
80 mph82.8 mph+2.8 mph

Each size on its own

Questions

Which is bigger, 245/50R18 or 245/55R18?
245/55R18 is taller by 0.96 inches (28.61" vs 27.65"). 245/50R18 is the same width.
Can I replace 245/50R18 with 245/55R18?
It is not recommended without checking carefully. The diameter difference is +3.5%, 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 245/55R18 change my speedometer?
When your speedometer reads 60 mph with 245/55R18 fitted (calibrated for 245/50R18), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.5%.
Will 245/55R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.48 inches of ground clearance at the axle.

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