How to Bend a Rod… and Why to Forget About it Afterwards

Surfing the internet the other day I came across an article that called my attention due to this statement:

Ongoing advancements in fly line materials and design continue to offer anglers ways to get more out of their casts. Today’s fly lines load rods more effectively…”

So I think it is 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 a change in the velocity of a body.
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 acceleration required comes from the caster’s arm. Mass comes from the weight of the rod itself and of the line being cast. The bigger the acceleration the bigger the force, even if the mass doesn’t change. The bigger the mass the bigger the resultant force, even 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, that line should have an increase of its 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 printed 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, as some people say, with the inability of the average fly angler to properly adapt to the rigidity of some modern fly rods. And, IMHO, it isn’t a good idea whatsoever; but that would be a topic for another article.

On the other hand, apart from its naivety, the problem with that quote above is that it prompts fly anglers to look in the wrong direction regarding fly casting.

The fundamental issue with a casting model based on rod load is that nobody knows what a proper rod load is for a given cast; I haven’t met anybody able to look at the bend in a rod during a casting stroke and tell if it is a proper load or not. And that is for a reason. Not only different rods will show different amounts of bend for the same cast, even different anglers can get different amounts of rod bend for the same casting distance with the same rod, depending on their individual casting styles.
Let’s take a deeper look at this heretical statement.

Fly line speed comes from two sources: force and distance (i.e. the distance over which that force is applied).
This is one of the circumstances in which the Physics concept of Work is essential to properly understand things, as the formula for Work (W = F.d ; F being force and d being distance) is what puts those two elements in relation.
Work is equivalent to kinetic energy, and kinetic energy is equivalent to line velocity in practical casting terms.
An everyday example comes in handy to understand this. Start the engine of your car and push the gas pedal; it is just common sense that the longer the distance covered by the vehicle, the higher its speed, even without varying the pushing from our foot. We can say that, for a constant force (we keep the gas pedal in the same position), the longer the distance the higher the speed.
Looking from another point of view, you can get the same Work —that is, the same line speed— by applying:

  • A relatively small force over a long distance.
  • A relatively big force over a short distance.

In the case of fly casting, casting stroke length is equivalent to distance, and rod rotation is equivalent to force.
The corollary of this line of reasoning is that different amounts of force can give you the same fly line speed, and this implies that rod load is different in each case: our rod gets bent due to force, and, obviously, a bigger force will bend it more than a small force will do.

In this way, what we have is that the pretty compact casting stroke of Steve Rajeff —a very powerful caster, able of applying a lot of force to a rod over a short distance— will result in a bigger load than a slower and longer stroke, however both casts will send the fly to the same distance.

Rod load is an overstated concept. Mel Krieger used it as a tool to fix the problem of those students who performed their casting strokes at a close to constant speed. By asking them to try to load the rod, he was teaching how to properly accelerate the rod butt to get a good cast.
Apart from that, I don’t see the rod load concept having any other application in practical fly casting terms. That is why I found the quote opening this article rather weird.

8 comments on “How to Bend a Rod… and Why to Forget About it Afterwards

  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

  5. Good post.
    Modern taper designs change the mass distribution on a line. Manuafacturers play around where within the first 30 ft they distribute the weight to try to provide the caster with more mass closer to the tip for some of their lines. Older line design typically had a front taper , and level line and a back taper. (And running line for wf lines) Rather than having a long section of level line newer designs have shorter or no mid level section but have a looooong back taper. Effectively pushing weight forward in the design . Trying to make the first 20/25 Ft heavier than a simpler taper design.

    For small stream fishing these taper designs are (in my opinion) are not really necessary.

    A brief option piece I wrote on small stream lines..

    Liked by 1 person

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