We present the results of a modest grid of three-dimensional (SPH) simulations of nearly head-on collisions between two model galaxies, each consisting of a rigid halo and a gas-rich disk component. The companion to primary mass ratio used is typically 0.2 - 0.35. Simple models of radiative cooling and heating from young star activity are also included in the simulations. Star formation is assumed to occur when the local gas density exceeds a threshold value. In these collisions the primary gas disk remains largely intact, though a gas bridge is splashed out between the two galaxies. Star formation occurs in asymmetric ring-like waves in the primary. The bridge is predicted to have essentially no ongoing star formation. These results agree with observations of the Cartwheel and VII Zw 466 ring galaxies.