  Radius inflation continues to be explored as a peculiar occurrence among
magnetically active, low-mass stars. Recently Somers et. al. 2017 showed that
radius inflation among low-mass stars in the young open cluster M45 (Pleiades
Cluster) is correlated to the rotation rate: faster rotators are more inflated.
Here we extend that work to a sample of 68 stars of the older open Hyades
Cluster. We derive the stars' spectral energy distributions to measure their
bolometric fluxes. With spectroscopically defined $T_{\rm eff}$ and {\it
Gaia\/} distances we calculate stellar radii using the Stefan-Boltzmann
relation. We find numerous stars that exhibit significant (3-4$\sigma$) radius
inflation relative to a nominal cluster isochrone. We compare these results to
that of the younger Pleiades and consider radius inflation as a function of
open cluster evolution. We find that unlike the Pleiades, there is not a
statistically significant correlation between radius inflation and stellar
rotation period. However, we do find that most inflated stars have (rapid)
rotational Rossby numbers of 0.1--0.2, such that the correlation of radius
inflation with Rossby number is statistically significant at 99.98\%
confidence. Since the canonical rotation-activity relation of low-mass stars is
understood to result from the connection between magnetic activity and surface
convection, our results imply that magnetic activity within the convective
layers of low-mass stars is what preferentially drives radius inflation
