Hypersonic boundary layer stability and transition for two different cone geometries at Mach 6 are studied using direct numerical simulation (DNS). The two geometries are (i) the flared cone investigated in the NASA Langley Test Chamber Facility1 and (ii) its straight (non-ared) counterpart. We present a detailed comparison between these geometries with respect to the base flow, i.e. the undisturbed laminar flow, and the linear stability regime. Furthermore, a parameter study regarding secondary fundamental instability was performed for each geometry. Then a wave which experienced a high secondary growth rate was used to initialize numerical simulations deep into the transitional regime. The resulting nonlinear process, which can be considered to be a 'classical' fundamental (K- type) breakdown, is analyzed in detail. By comparing the results for the two different geometries, qualitative and quantitative insight into the hypersonic transition process for flared cones is obtained. In particular the question how strong the nonlinear transition process is altered by the cone flare is discussed.