Tire Size Box

215/35R18 vs 215/40R18

215/40R18 compared with 215/35R18

+3.5% diameter, 0.0" width

215/40R18 is 24.77" tall vs 23.93". More than the 3% rule of thumb, so check carefully before switching.

23.9"18" rim3.0"8.5" wide
215/35R18 (solid) compared with 215/40R18 (dashed outline), drawn to scale

With 215/40R18 tires, when your speedometer says 60 mph you are really going

62.1 mph

215/40R18 is +0.85 inches (+3.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

215/35R18215/40R18Difference%
Overall diameter23.93"24.77"+0.85"+3.5%
Section width8.46"8.46"0.00"0.0%
Sidewall height2.96"3.39"+0.42"+14.3%
Circumference75.16"77.82"+2.66"+3.5%
Revolutions per mile843.0814.2−28.8−3.4%

Speedometer difference

If your vehicle came with 215/35R18 and you fit 215/40R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.1 mph+1.1 mph
40 mph41.4 mph+1.4 mph
50 mph51.8 mph+1.8 mph
60 mph62.1 mph+2.1 mph
65 mph67.3 mph+2.3 mph
70 mph72.5 mph+2.5 mph
75 mph77.7 mph+2.7 mph
80 mph82.8 mph+2.8 mph

Each size on its own

Questions

Which is bigger, 215/35R18 or 215/40R18?
215/40R18 is taller by 0.85 inches (24.77" vs 23.93"). 215/35R18 is the same width.
Can I replace 215/35R18 with 215/40R18?
It is not recommended without checking carefully. The diameter difference is +3.5%, 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 215/40R18 change my speedometer?
When your speedometer reads 60 mph with 215/40R18 fitted (calibrated for 215/35R18), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.5%.
Will 215/40R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.42 inches of ground clearance at the axle.

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