Tire Size Box

295/35R18 vs 285/40R18

285/40R18 compared with 295/35R18

+3.2% diameter, −0.4" width

285/40R18 is 26.98" 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 285/40R18 (dashed outline), drawn to scale

With 285/40R18 tires, when your speedometer says 60 mph you are really going

61.9 mph

285/40R18 is +0.85 inches (+3.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

295/35R18285/40R18Difference%
Overall diameter26.13"26.98"+0.85"+3.2%
Section width11.61"11.22"−0.39"−3.4%
Sidewall height4.06"4.49"+0.42"+10.4%
Circumference82.09"84.75"+2.66"+3.2%
Revolutions per mile771.8747.6−24.2−3.1%

Speedometer difference

If your vehicle came with 295/35R18 and you fit 285/40R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph31.0 mph+1.0 mph
40 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.1 mph+2.1 mph
70 mph72.3 mph+2.3 mph
75 mph77.4 mph+2.4 mph
80 mph82.6 mph+2.6 mph

Each size on its own

Questions

Which is bigger, 295/35R18 or 285/40R18?
285/40R18 is taller by 0.85 inches (26.98" vs 26.13"). 295/35R18 is wider by 0.39 inches.
Can I replace 295/35R18 with 285/40R18?
It is not recommended without checking carefully. The diameter difference is +3.2%, 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 285/40R18 change my speedometer?
When your speedometer reads 60 mph with 285/40R18 fitted (calibrated for 295/35R18), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.2%.
Will 285/40R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.42 inches of ground clearance at the axle.

Other comparisons