The children's bicycles' tires' air pressure's impact on their rides' smoothness was significant.
Let's break down the possessive and plural nouns:
* children's: possessive plural noun
* bicycles': possessive plural noun
* tires': possessive plural noun
* air pressure's: possessive singular noun (but it's part of the plural phrase "tires' air pressure")
* rides': possessive plural noun
Let me know if you'd like to try another sentence!