Tire Size Box

275/45R18 vs 275/50R18

275/50R18 compared with 275/45R18

+3.9% diameter, 0.0" width

275/50R18 is 28.83" tall vs 27.74". More than the 3% rule of thumb, so check carefully before switching.

27.7"18" rim4.9"10.8" wide
275/45R18 (solid) compared with 275/50R18 (dashed outline), drawn to scale

With 275/50R18 tires, when your speedometer says 60 mph you are really going

62.3 mph

275/50R18 is +1.08 inches (+3.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

275/45R18275/50R18Difference%
Overall diameter27.74"28.83"+1.08"+3.9%
Section width10.83"10.83"0.00"0.0%
Sidewall height4.87"5.41"+0.54"+11.1%
Circumference87.16"90.56"+3.40"+3.9%
Revolutions per mile726.9699.6−27.3−3.8%

Speedometer difference

If your vehicle came with 275/45R18 and you fit 275/50R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.6 mph+1.6 mph
50 mph52.0 mph+2.0 mph
60 mph62.3 mph+2.3 mph
65 mph67.5 mph+2.5 mph
70 mph72.7 mph+2.7 mph
75 mph77.9 mph+2.9 mph
80 mph83.1 mph+3.1 mph

Each size on its own

Questions

Which is bigger, 275/45R18 or 275/50R18?
275/50R18 is taller by 1.08 inches (28.83" vs 27.74"). 275/45R18 is the same width.
Can I replace 275/45R18 with 275/50R18?
It is not recommended without checking carefully. The diameter difference is +3.9%, 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 275/50R18 change my speedometer?
When your speedometer reads 60 mph with 275/50R18 fitted (calibrated for 275/45R18), your real speed is 62.3 mph. Your odometer will under-count miles by about 3.9%.
Will 275/50R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.54 inches of ground clearance at the axle.

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