Originally Posted by randyflycaster
I meant WF. Most casters will cast farther with a WF line, perhaps, but when it comes to real long casts, Steve Rajeff said a DT allows really good casters to carry more line. A fly rod is designed to handle a certain amount of weight. If it's overloaded it slows down and the line/cast doesn't go as far; so 60 feet of a DT weighs less than 60 feet of a WF line.
I think you have it reversed. A WF has a rear taper that goes into a running line. A DT has only the front taper and then a long belly section that goes into the taper on the other end so that the line can be turned around.
Unless you have a longbelly WF line, the first 60 feet of a Wf line will weigh less than the first 60 feet of a DT line.
As the drawing below shows at 60 feet the WF line is into the running line so it has less mass over the first 60 feet that the DT line.