How to Bend a Rod


I stumbled upon the quote above the other day and thought that it was worth talking a little bit about “rod load” or, as I prefer to say, “rod bend”.

There is only one thing able of bending a rod: force.

Force is related to mass and acceleration as per the formula: F = m.a.

Mass is the amount of matter of a body; on planet Earth it is equivalent to weight —and, to my knowledge, there aren’t any fly rods available in the Moon. Acceleration is an increase of velocity.

What this formula means is that if a force is applied to an object, that object will increase its velocity.

Back to our fly rod, we need a force to bend it. The needed acceleration comes from the caster’s arm. Mass comes from the weight of the rod itself and of the line being cast. The bigger the mass the bigger the resultant force, if the acceleration applied is the same.

So what is the requirement in a line for it to bend the rod more, for the same acceleration applied to the rod butt? Obviously to increase it mass, i.e. its weight. You don’t need much technology to put more plastic material in a line, do you? In fact if you were a line manufacturer you wouldn’t need to change your production process at all, just put the lines formerly labeled as #6 weight —or even #7— in a spool and box with a #5 on them.

Some time ago, line manufacturers started increasing the weight of their lines, while keeping the same AFFTA number on them —throwing that standard out of the window in the process. It doesn’t have anything to do with technology, but, maybe, with the inability of the average fly angler to properly use the ever increasing rigidity of modern fly rods. And, IMHO, it isn’t a good idea whatsoever; but that would be a topic for another article.

7 comments on “How to Bend a Rod

  1. Henry K. says:

    I totally agree with what you have written. To add to what you have said about fly fishers up lining their rods to get them to bend/load more, I have found that the discussion is ALWAYS about the line mass/wt being more, and rarely if ever about the taper of the line. A front loaded line will load the rod more effectively than a gradually tapered “presentation” fly line.

    In one recent discussion, a poster said the Rio Gold was a 5.5 wt line when it is actually on the heavy end of the AFTMA 5 wt line scale. Another said he uses the Rio Grande because it is a full line wt heavier, which it is.

    Neither poster commented on the fact that the tapers of the two lines are very different. the Rio Gold has a gradual taper. The Rio Grand is not only a full line wt heavier, its mass is loaded toward the front of the line. Of course it will load the rod better. So there is a lack of understanding of fly line design.

    Whether a fly fisher is going to upload a rod or not, they should choose the fly line taper design for the type of fishing they will be doing. Then they can choose the fly line mass that will load the rod.


  2. In my experience the resistance, which a fly line provides during the rotation of the rod, is what determines a high percentage of the FEEL in fly casting. Line mass is one part of the resistance. Line surface is the other (big) one, yet often underestimated for it’s impact on the feel! An interesting question to the line industrie experts might be about the impact on feel for those line coming with textured coatings reducing drag upto 60%. 60% is what one of the leading companies told me to have been achieved on their new lines (last year)! In the end it’s all about advertising forward to the majority of customers, who don’t know much about it.


  3. tonyking74 says:

    I feel that we as instructors are complicit in all this we have all at some time been advocates of not over lining rods to give more feel. We have helped created a climate where pride alone encourages the sale of a 7# marked as a 5# and the market has proved that to be true. Now what do we do encourage underling ” Okay you cast better now with your 5#(7#) lets try that with a 4# (5-6#)” .


  4. paracaddis says:

    Aitor I am on your page and have been for a long time on this matter. The public have been misled and it makes things very tricky for a beginner.. If you will forgive the intrusion a link to a story : hopefully will amuse some of your readers.

    Liked by 2 people

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