Tire Size Box

265/35R18 vs 265/40R18

265/40R18 compared with 265/35R18

+4.1% diameter, 0.0" width

265/40R18 is 26.35" tall vs 25.30". More than the 3% rule of thumb, so check carefully before switching.

25.3"18" rim3.7"10.4" wide
265/35R18 (solid) compared with 265/40R18 (dashed outline), drawn to scale

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

62.5 mph

265/40R18 is +1.04 inches (+4.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

265/35R18265/40R18Difference%
Overall diameter25.30"26.35"+1.04"+4.1%
Section width10.43"10.43"0.00"0.0%
Sidewall height3.65"4.17"+0.52"+14.3%
Circumference79.49"82.77"+3.28"+4.1%
Revolutions per mile797.1765.5−31.6−4.0%

Speedometer difference

If your vehicle came with 265/35R18 and you fit 265/40R18, 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 mph52.1 mph+2.1 mph
60 mph62.5 mph+2.5 mph
65 mph67.7 mph+2.7 mph
70 mph72.9 mph+2.9 mph
75 mph78.1 mph+3.1 mph
80 mph83.3 mph+3.3 mph

Each size on its own

Questions

Which is bigger, 265/35R18 or 265/40R18?
265/40R18 is taller by 1.04 inches (26.35" vs 25.30"). 265/35R18 is the same width.
Can I replace 265/35R18 with 265/40R18?
It is not recommended without checking carefully. The diameter difference is +4.1%, 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 265/35R18), your real speed is 62.5 mph. Your odometer will under-count miles by about 4.1%.
Will 265/40R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.52 inches of ground clearance at the axle.

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