Let $G$ be a finitely generated nilpotent group of class $c$. Let $r=\text{rank}(G/[G,G])$ (i.e., the number of infinite cyclic summands of $G/[G,G]$).
Are there inequalities relating $c$ and $r$? (if so, are they tight?)
EDIT: There is a simple answer in the comments below.
Groups of maximal class are an interesting source of examples.
N. Blackburn has described among others the metabelian $p$-groups of maximal class, for $p > 3$. These are two-generated, and have arbitrarily large class. They can also be described handily with a modicum of number theory, see for instance the book
The theory of basic commutators allows one to use free nilpotent groups as rather general examples.