Thule makes an adapter for bikes where the top tube is at too much of an angle for proper use on a carrier--such as a women's BMX or an unusual frame(like the townie). I would contact Thule(other carrier brands may have something similar) and ask about using the adapter with a Townie.

http://www.thule.com/en-US/US/Produc...Frame-Adapter#


Here's a Google search of top tube frame adapters.

http://www.google.com/search?q=tube+...w=1377&bih=765