CME propagation: where does solar wind drag 'take over'?

Coronal mass ejections (CMEs) from the Sun are known to be acted upon by driving as well as drag forces. They are generally thought to be driven by Lorentz self-forces, while the drag is due to viscous interaction with the ambient solar wind. However, the typical heliocentric distances at which driving forces cease to be dominant (and solar wind drag becomes important) is not obvious for most CMEs. We use a recently developed microphysical model for solar wind viscous drag (Subramanian, Lara and Borgazzi 2012) together with data for driving forces from a well observed set of flux rope CMEs to answer this question. These results are important for building quantitative models for CME propagation, especially for those CMEs which are not fast enough for one to assume that they are acted upon primarily by drag forces.