Tire Size Box

265/40R18 vs 265/45R18

265/45R18 compared with 265/40R18

+4.0% diameter, 0.0" width

265/45R18 is 27.39" tall vs 26.35". More than the 3% rule of thumb, so check carefully before switching.

26.3"18" rim4.2"10.4" wide
265/40R18 (solid) compared with 265/45R18 (dashed outline), drawn to scale

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

62.4 mph

265/45R18 is +1.04 inches (+4.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

265/40R18265/45R18Difference%
Overall diameter26.35"27.39"+1.04"+4.0%
Section width10.43"10.43"0.00"0.0%
Sidewall height4.17"4.69"+0.52"+12.5%
Circumference82.77"86.05"+3.28"+4.0%
Revolutions per mile765.5736.3−29.2−3.8%

Speedometer difference

If your vehicle came with 265/40R18 and you fit 265/45R18, 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 mph62.4 mph+2.4 mph
65 mph67.6 mph+2.6 mph
70 mph72.8 mph+2.8 mph
75 mph78.0 mph+3.0 mph
80 mph83.2 mph+3.2 mph

Each size on its own

Questions

Which is bigger, 265/40R18 or 265/45R18?
265/45R18 is taller by 1.04 inches (27.39" vs 26.35"). 265/40R18 is the same width.
Can I replace 265/40R18 with 265/45R18?
It is not recommended without checking carefully. The diameter difference is +4.0%, 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 265/45R18 change my speedometer?
When your speedometer reads 60 mph with 265/45R18 fitted (calibrated for 265/40R18), your real speed is 62.4 mph. Your odometer will under-count miles by about 4.0%.
Will 265/45R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.52 inches of ground clearance at the axle.

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