For the SRT trail:

Ride West River Dr or Kelly Dr away from the city.

If West River, make a right onto Falls Bridge at the end of West River and then left onto Kelly Dr.

Follow that around (pass a bus terminal and over the Wissahickon creek) to Main St. in Manayunk. There is a sign. Stay to the left of the fork.

Stay on Main St through Manayunk.

Then make right onto Leverington St. when you come to a Y. And then first left onto Umbria St. Nice hill on Umbria!

Follow that around a bend, and then sharp left (watch for cars!) onto Shawmont Ave.

Then you pick up the train again on your right. Take that as far as you want, all the way to Phoenixville for a 60+ roundtrip from Center City.

In city riding:

Spring Garden St has a nice bike lane.

Ride north into Fairmount and then ride E-W on Spring Garden for some nice city views.