  The transverse momentum dependent distributions (TMD) are an essential part
of the factorization theorems in vector boson production. They are
non-perturbative, double scale dependent functions that asymptotically match
onto collinear parton distributions functions (PDF). Once TMD are expressed
using PDF, one observes that they are sensitive to the choice and quality of
PDF sets (PDF bias). A solution to this problem is found and discussed.
Nevertheless the main source of error on vector boson spectra still comes from
PDF uncertainty propagation.
