Firstly After flocking what I do far all urban bases is base coat the stuff black. I try to get everything coated in back but if some flock isn't covered that's fine. The later stages should deal with that.
And there are the bases done. What I did here was drybrushed codex and fortress gray over the black. For the yellow striping I used Iyanden Darksun foundation as it is nice and flat. Now there are 2 ways I dry brush urban. If I want it to be a non street urban base I make it very grey with codex grey. If I want it more of a urban street its a light drybrush of the grey so the black bleeds through the drybrushing. That's pretty much it. As I said when i do more of these bases ill make an additional post for urban showing the base in more detail.
One quick note. These new biker bases are great. As you can see the bikes sit fine on them. As far as I know there only available with the scout bikes but you can buy them in groups of 5 off Games Workshop's website. Well until next time... Take care.