  Massive star clusters are often used as tracers of galaxy formation and
assembly. In order to do so, we must understand their properties at formation,
and how those properties change with time, galactic environment, and galaxy
assembly history. The two most important intrinsic properties that govern star
cluster evolution are mass and radius. In this paper, we investigate 10
theoretically and observationally motivated initial size-mass relations for
star clusters, and evolve populations of clusters through galaxy formation
models. We compare our results to each other and to observations of cluster
populations in M83, M31, and the Milky Way. We find that none of our size-mass
relations agree with the observations after 6-10 Gyr of evolution. We can
successfully reproduce the cluster mass functions with models that have a small
range of initial radii, and which do not allow cluster radii to change with
time. However, these models do not agree with our understanding of cluster
evolution, which does involve radius evolution, and do not match the observed
distributions of radii. We note that there is a region of parameter space where
clusters are optimally protected from both tidal shocks and evaporation due to
two-body relaxation. Clusters which are allowed to evolve into this parameter
space will likely survive. An improved understanding of both mass and radius
evolution of star clusters in realistic, time-varying galactic potentials is
necessary to appropriately make the connection between present-day cluster
properties and their use as tracers of galaxy formation and assembly.
