just look at google earth and head towards caerau forrest where it leads to croeserw. Croeserw is the top of that vally and you can roll down to whites or the wall from there. Whites being the quickest from there. There is path you can join in cymmer.
From what i can tell from all the areas around there and the other side of Afan (cimla) where i am from you can jump on all the fire roads you can see on the map.
why dont you strava the area and see of there are any specific routes in the area. I know the boys from Rush Cycles ride around there frequently.