Tire Size Box

295/35R18 vs 295/40R18

295/40R18 compared with 295/35R18

+4.4% diameter, 0.0" width

295/40R18 is 27.29" tall vs 26.13". More than the 3% rule of thumb, so check carefully before switching.

26.1"18" rim4.1"11.6" wide
295/35R18 (solid) compared with 295/40R18 (dashed outline), drawn to scale

With 295/40R18 tires, when your speedometer says 60 mph you are really going

62.7 mph

295/40R18 is +1.16 inches (+4.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

295/35R18295/40R18Difference%
Overall diameter26.13"27.29"+1.16"+4.4%
Section width11.61"11.61"0.00"0.0%
Sidewall height4.06"4.65"+0.58"+14.3%
Circumference82.09"85.74"+3.65"+4.4%
Revolutions per mile771.8739.0−32.8−4.3%

Speedometer difference

If your vehicle came with 295/35R18 and you fit 295/40R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.3 mph+1.3 mph
40 mph41.8 mph+1.8 mph
50 mph52.2 mph+2.2 mph
60 mph62.7 mph+2.7 mph
65 mph67.9 mph+2.9 mph
70 mph73.1 mph+3.1 mph
75 mph78.3 mph+3.3 mph
80 mph83.6 mph+3.6 mph

Each size on its own

Questions

Which is bigger, 295/35R18 or 295/40R18?
295/40R18 is taller by 1.16 inches (27.29" vs 26.13"). 295/35R18 is the same width.
Can I replace 295/35R18 with 295/40R18?
It is not recommended without checking carefully. The diameter difference is +4.4%, 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 295/40R18 change my speedometer?
When your speedometer reads 60 mph with 295/40R18 fitted (calibrated for 295/35R18), your real speed is 62.7 mph. Your odometer will under-count miles by about 4.4%.
Will 295/40R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.58 inches of ground clearance at the axle.

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