Tire Size Box

275/35R18 vs 265/40R18

265/40R18 compared with 275/35R18

+3.0% diameter, −0.4" width

265/40R18 is 26.35" tall vs 25.58". More than the 3% rule of thumb, so check carefully before switching.

25.6"18" rim3.8"10.8" wide
275/35R18 (solid) compared with 265/40R18 (dashed outline), drawn to scale

With 265/40R18 tires, when your speedometer says 60 mph you are really going

61.8 mph

265/40R18 is +0.77 inches (+3.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

275/35R18265/40R18Difference%
Overall diameter25.58"26.35"+0.77"+3.0%
Section width10.83"10.43"−0.39"−3.6%
Sidewall height3.79"4.17"+0.38"+10.1%
Circumference80.36"82.77"+2.41"+3.0%
Revolutions per mile788.5765.5−23.0−2.9%

Speedometer difference

If your vehicle came with 275/35R18 and you fit 265/40R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph30.9 mph+0.9 mph
40 mph41.2 mph+1.2 mph
50 mph51.5 mph+1.5 mph
60 mph61.8 mph+1.8 mph
65 mph67.0 mph+2.0 mph
70 mph72.1 mph+2.1 mph
75 mph77.3 mph+2.3 mph
80 mph82.4 mph+2.4 mph

Each size on its own

Questions

Which is bigger, 275/35R18 or 265/40R18?
265/40R18 is taller by 0.77 inches (26.35" vs 25.58"). 275/35R18 is wider by 0.39 inches.
Can I replace 275/35R18 with 265/40R18?
It is not recommended without checking carefully. The diameter difference is +3.0%, 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 265/40R18 change my speedometer?
When your speedometer reads 60 mph with 265/40R18 fitted (calibrated for 275/35R18), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.0%.
Will 265/40R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.38 inches of ground clearance at the axle.

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