Fly rods come in a variety of “actions,” from slow to super-fast. As we have written about before, the action of a rod is determined by a variety of factors, such as materials, taper, and hardware. But it’s also important to know that any discussion of rod action must also take into account the role of the fly line. Because line mass affects how a fly rod loads and unloads, a given rod will perform differently when paired with different lines. It helps, then, to look at the rod and the line as an integrated system.
When you are evaluating rods, string them up with the line you’ll actually be using when you fish. The taper of the line is important because it determines how much mass will be outside the rod tip at a given length, say 35 feet. For instance, a line with a long front taper will not load a rod the same way a bass-bug taper—with more mass concentrated at the tip—will. By using your line and casting at your usual fishing distance, you’ll get a better sense for how a particular rod will feel and perform when you finally get on the water.
Some anglers choose to overline or underline their rods to tweak the action, although it is difficult to underline some very stiff, fast rods. For finer adjustments, there are even lines available in half-weight line sizes.