A bicycle handlebar assembly comprises a base bar, a v-shaped stem selectively removable from the base bar, and a bicycle fork assembly. Control cables from the bicycle may be routed from the base bar into hollow diverging stem members of the v-shaped stem. The bicycle fork assembly comprises an external-steerer fork having a load-bearing member and a preload tensioning rod. The preload tensioning rod fits within a head tube of the bicycle, and a hollow space around the preload tensioning rod accommodates control cables passing from the v-shaped stem into a hollow portion of the bicycle frame. The v-shaped stem is secured against the base bar by a pair of nut plates. In some examples, an engagement portion of an accessory such as an aerobar extension assembly is configured to secure the v-shaped stem and an aerobar extension against the base bar.