  We study the conductivity of two-dimensional graphene-type materials with
tilted cones as well as their three-dimensional Weyl counterparts and show that
a covariant quantum Boltzmann equation is capable of providing an accurate
description of these materials' transport properties. The validity of the
covariant Boltzmann approach is corroborated by calculations within the Kubo
formula. We find a strong anisotropy in the conductivities parallel and
perpendicular to the tilt direction upon increase of the tilt parameter $\eta$,
which can be interpreted as the boost parameter of a Lorentz transformation.
While the ratio between the two conductivities is $\sqrt{1-\eta^2}$ in the
two-dimensional case where only the conductivity perpendicular to the tilt
direction diverges for $\eta\rightarrow 1$, both conductivities diverge in
three-dimensional Weyl semimetals, where $\eta=1$ separates a type-I (for
$\eta<1$) from a type-II Weyl semimetal (for $\eta>1$).
