Tire Size Box

265/50R17 vs 265/45R18

265/45R18 compared with 265/50R17

−0.2% diameter, 0.0" width

265/45R18 is 27.39" tall vs 27.43". Within the 3% rule, so usually interchangeable.

27.4"17" rim5.2"10.4" wide
265/50R17 (solid) compared with 265/45R18 (dashed outline), drawn to scale

With 265/45R18 tires, when your speedometer says 60 mph you are really going

59.9 mph

265/45R18 is −0.04 inches (−0.2%) in overall diameter. That is within the 3% most shops and makers allow.

265/50R17265/45R18Difference%
Overall diameter27.43"27.39"−0.04"−0.2%
Section width10.43"10.43"0.00"0.0%
Sidewall height5.22"4.69"−0.52"−10.0%
Circumference86.18"86.05"−0.14"−0.2%
Revolutions per mile735.2736.3+1.2+0.2%

Speedometer difference

If your vehicle came with 265/50R17 and you fit 265/45R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.0 mph0.0 mph
30 mph30.0 mph0.0 mph
40 mph39.9 mph−0.1 mph
50 mph49.9 mph−0.1 mph
60 mph59.9 mph−0.1 mph
65 mph64.9 mph−0.1 mph
70 mph69.9 mph−0.1 mph
75 mph74.9 mph−0.1 mph
80 mph79.9 mph−0.1 mph

Each size on its own

Questions

Which is bigger, 265/50R17 or 265/45R18?
265/50R17 is taller by 0.04 inches (27.43" vs 27.39"). 265/50R17 is the same width.
Can I replace 265/50R17 with 265/45R18?
Usually, yes. The diameter difference is −0.2%, inside the 3% rule of thumb most tire shops use. Check that the wider or taller tire clears your suspension and fenders, and that its load index meets your placard.
How much will 265/45R18 change my speedometer?
When your speedometer reads 60 mph with 265/45R18 fitted (calibrated for 265/50R17), your real speed is 59.9 mph. Your odometer will over-count miles by about 0.2%.
Will 265/45R18 lift my vehicle?
Ride height changes by half the diameter difference: −0.02 inches of ground clearance at the axle.

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