Leaf springs do their job whether they’re smiling or frowning. Some do their job with a completely flat expression. They all do their job well, if that was how the manufacturer designed it.
A question we get asked many times is what way should my leaf springs be bowed on my vehicle? Should it be bowed upward, like smiling, flat, or downward like frowning?
While many manufacturers designed their springs to be smiling, some like Chrysler rear springs and GM 4×4 front springs are designed to be bowed downward or frowning.
A leaf spring does not care which way it is bowed for they will work either way. So the correct answer is yes, depending on the vehicle make and desired ride height.