April 12, 2021 3 min read

Overlining (and Underlining) a Fly Rod

“Overlining” a fly rod refers to the practice of using a fly line that is rated higher than the designation on your fly rod. Eg using a 6wt fly line on a fly rod designated as a ‘5wt’.

Underlining a fly rod is the reverse I.e using a 5wt fly line on a fly rod designated by the manufacturer as a ‘6wt’ fly rod.

This all gets a little sketchy these days because:

  1. There is no standard to label the intrinsic power of a fly rod. And many fly rod manufacturers produce fly rods that would normally be stiffer than would be a fair designation in their pursuit to sell “fast fly rods”. For some reason the perception is that faster is better and consumers go for this as being some sort of benefit.
  2. Many fly lines are over - and in some cases way over - the weight designation for fly line specifications. There is a standard specification for fly lines - not so for fly rods as outlined in our earlier article here: https://swiftflyfishing.com/blogs/news/fly-fishing-fly-rod-ratings-fly-line-weights-and-the-arms-race

It's important to know that overlining or underlining a fly rod will not change it’s intrinsic properties. It will, all things being equal, make it bend more or less for a given amount of line out the rod tip.

5 wt fly rod

Overlining a fly rod:

Why you might wish to overline your fly rod.

  • Casting short distances in windy conditions
  • Picking up and turning over very large flies
  • Lots of roll casting in confined spaces / no backcast room
  • Loading (Bending) the rod with a short amount of line out the tip
  • You have a stupidly stiff fly rod that the manufacture has underrated in order to make it feel “fast”

Keep in mind that many fly lines are now over the AFFTA recommended weight for the specification - so in many cases you are already casting an “over-lined” fly rod by default

Underlining a fly rod:

All things being equal - a lighter line will deflect / bend the rod less for a given amount of line out.

This can:

  • Result in tighter loops
  • Allow a longer carry
  • Give a more delicate presentation than a heavier line.

 Overlining fly rods

Over-lining a fly rod

If you look at the actual weight stated on fly line specifications above, you’ll see that many fly lines are heavier than the highest limit of the specification.

The problem then is that unless you’re aware of that when you buy the fly line, you might be overlining a fly rod that is already effectively overlined.

The AFFTA system, is not perfect, but if line manufacturers kept their products in line with the standard specifications there would at least be a “standard” and all our lives would be made much easier. Then, you could adjust up or down for your rod type without having to double-check that the specifications of the line matched the standard.

Our Glassline fly lines - produced for us by Scientific Anglers USA match the sweet spot for a given weight exactly. Epic Glassine  fly lines - True to weight fly lines 

Our fly rods are rated against the AFFTA standard for each line - and are, to the fullest extent possible - true to weigh. Epic Studio Built Fly Rods - True to Weight Fly Rods

More on this topic:

Fly Fishing: Fly Rod Ratings, Fly Line Weights and the Arms Race

How to choose the right fly line for your fly rod

5 Responses

Greg Ness
Greg Ness

April 28, 2021

Love fishing !!!

Ronsld beach
Ronsld beach

April 28, 2021

Shure wouldent mind wining this fine looking set up i tell you what it looks all kinds of nice

ritch phillips
ritch phillips

April 28, 2021

this is a very clear response for stupidly wt’ed fly rods…..I personally over line most of my rods for a smoother feel and the ole slingshot effect…also suits my casting style…if there is such a thing……for me I use a heavier line to gain a little more distance with larger flies…and its just smoother in almost all circumstances…at least for me…
my personal experience with underlining..well i have watched friends of mine forcing casts to large fish..using a line wt designated for the rod they were using…meeeeeow…resulting in a hinging and a very slight rod separation at the ferrule.often resulting in casting rod tips down the line on more than one occasion and broken rods at the ferrule when setting the hook on fairly large salmon…on more than ne occasion….ah the fast rod designation…….these were not inexpensive off brand rods were talking about here…..either…
this is a great article…..thanks…….what about those AIR FLO lines wt’ed at a line and a half over the rods they are supposed to work…yipes…why not just call an 9wt a nine and not an 8wt…..well…enough of my blather….thanks again for the great info…..if i had a bundle i would definitely buy your 8wt 888 rod……meoooooow..what a slingshot …with the right line ritchp

Herman Breedt
Herman Breedt

April 28, 2021

I enjoy fishing with a delicate 4 weight and I underline as the rod is a soft and slow and I find the rod copes better and so does my casting for that matter!

Michael Gregg
Michael Gregg

April 28, 2021

That, in this health-conscious era, so many overweight fly rods gets fitted with overweight lines, creating a generation of overweight tackle families, is simply shameful. There needs to be a Government Enquiry. Until then remember, the only safe practice is to slim down by specifying safe standards from your rod studio. Practice safe spey, kids.

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