Tire Size Box

245/45R18 vs 245/50R18

245/50R18 compared with 245/45R18

+3.6% diameter, 0.0" width

245/50R18 is 27.65" tall vs 26.68". More than the 3% rule of thumb, so check carefully before switching.

26.7"18" rim4.3"9.6" wide
245/45R18 (solid) compared with 245/50R18 (dashed outline), drawn to scale

With 245/50R18 tires, when your speedometer says 60 mph you are really going

62.2 mph

245/50R18 is +0.96 inches (+3.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

245/45R18245/50R18Difference%
Overall diameter26.68"27.65"+0.96"+3.6%
Section width9.65"9.65"0.00"0.0%
Sidewall height4.34"4.82"+0.48"+11.1%
Circumference83.82"86.85"+3.03"+3.6%
Revolutions per mile755.9729.5−26.4−3.5%

Speedometer difference

If your vehicle came with 245/45R18 and you fit 245/50R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.1 mph+1.1 mph
40 mph41.4 mph+1.4 mph
50 mph51.8 mph+1.8 mph
60 mph62.2 mph+2.2 mph
65 mph67.3 mph+2.3 mph
70 mph72.5 mph+2.5 mph
75 mph77.7 mph+2.7 mph
80 mph82.9 mph+2.9 mph

Each size on its own

Questions

Which is bigger, 245/45R18 or 245/50R18?
245/50R18 is taller by 0.96 inches (27.65" vs 26.68"). 245/45R18 is the same width.
Can I replace 245/45R18 with 245/50R18?
It is not recommended without checking carefully. The diameter difference is +3.6%, 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 245/50R18 change my speedometer?
When your speedometer reads 60 mph with 245/50R18 fitted (calibrated for 245/45R18), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.6%.
Will 245/50R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.48 inches of ground clearance at the axle.

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