  We present a comprehensive re-evaluation of the $ft$ values in superallowed
nuclear $\beta$ decays crucial for the precise determination of $V_{ud}$ and
low-energy tests of the electroweak Standard Model. It consists of the first,
fully data-driven analysis of the nuclear $\beta$ decay form factor, that
utilizes isospin relations to connect the nuclear charged weak distribution to
the measurable charge distributions. This prescription supersedes previous
shell-model estimations, and allows for a rigorous quantification of theory
uncertainties in $f$ which is absent in the existing literature. Our new
evaluation shows an overall downward shift of the central values of $f$ at the
level of 0.01\%.
