Just wanted to put in a plug for the GDB Sunday Roll ride...  it's a weekly "explore Dallas" ride that rolls at ~16 mph, for 30ish miles over the course of 3 hours, with one rest stop break.  If you enjoy a social pace, and discovering areas of Dallas that you've perhaps never knew existed, I encourage you to try this ride.  You don't have to be a GDB member to participate (in any GDB ride, actually)...
 
Note that this is not a "12-15mph" ride -- our typical rolling pace is about 16-17 on open stretches, and there will be the occasional hill to climb -- however, it is a "no drop" ride, so you won't get left out there somewhere unknown.  Other 'benters who have participated include Lynn (a regular), Shelley, Doug D, Squarecorners, Lawrie, and Sadowski, so you can ask them about it, too.   Doug D has been doing it recently on his carbon trike.
 
The ride leaves promptly at 9AM from the northeast corner of Preston/Royal, behind the Cantina Laredo and Einsteins Bagels.  We get back in the 12:00-12:30 timeframe.
 
I'm anticipating that we will ride through Downtown and to Fair Park this coming Sunday, to go see Big Tex before the fair starts up.
 
Paul

Here are the tracking routes for the last couple rides we've done, as an example.