  We present simulation data of first-order isotropic-to-nematic transitions in
lattice models of liquid crystals and locate the thermodynamic limit inverse
transition temperature $\epsilon_\infty$ via finite-size scaling. We observe
that the inverse temperature of the specific heat maximum can be consistently
extrapolated to $\epsilon_\infty$ assuming the usual $\alpha / L^d$ dependence,
with $L$ the system size, $d$ the lattice dimension and proportionality
constant $\alpha$. We also investigate the quantity $\epsilon_{L,k}$, the
finite-size inverse temperature where $k$ is the ratio of weights of the
isotropic to nematic phase. For an optimal value $k = k_{\rm opt}$,
$\epsilon_{L,k}$ versus $L$ converges to $\epsilon_\infty$ much faster than
$\alpha/L^d$, providing an economic alternative to locate the transition.
Moreover, we find that $\alpha \sim \ln k_{\rm opt} / {\cal L}_\infty$, with
${\cal L}_\infty$ the latent heat density. This suggests that liquid crystals
at first-order IN transitions scale approximately as $q$-state Potts models
with $q \sim k_{\rm opt}$.
