A Treatise on Static Testing and the Classification of Tenkara, Keiryu and Seiryu Rods

By Tom Davis

Ever since tenkara was widely introduced to the US fly fishing community by Daniel Galhardo, founder of Tenkara USA, there have been questions regarding the action or feel of tenkara rods. Questions began arising, such as, “how fast is that rod”, or “how slow is that rod”, or “does the rod have backbone”, or “will the rod protect my tippet”, etc. Since tenkara was essentially an unknown entity, breaking into a fly fishing tradition of relatively short, stiff western rods, it became apparent that some sort of classification was needed in which to better give the user an estimate of a rod’s overall action or feel.

To aid users in selecting a rod to fit their needs Galhardo instituted the Rod Action Index. This index follows the tradition of some Japanese rod makers where the rod is arbitrarily divided into ten sections and a ratio of sections above and below the flex point is numerically represented. In this ratio, the stiffer sections nearer the butt of the rod are to the left of the colon, while the flexible sections nearer the tip are to the right. For instance, a mid flex rod would have an Action Index of 5:5, meaning the flex point is halfway up the rod. A tip flex rod would be classified as a 7:3, meaning that the flex point is more near the top of the rod. Remember, the numbers do not represent the actual number of sections in the ratio. They add up to ten, an arbitrary number chosen to keep the system simple.

Courtesy of Tenkara USA. Used by permission.

It soon became apparent that although this basic action index may be adequate for some, it was not too helpful for a majority of individuals who wanted to begin exploring this newly introduced form of mountain stream fly fishing. Rather than embracing the simplicity of eastern thought, that is having fewer choices and working with and mastering what you have, many western fly fishers wanted more — more rod choices and more information regarding those rods. Western fly fishers come from a hyper-marketing paradigm where choice is king. Unfortunately, along with a myriad of choices comes confusion and questions. Which rod is right for me? Do I want a “fast” rod or a “slow” rod? What length is best? And on and on.

These questions are not unique to tenkara fishers. Western fly fisherman have been bombarded with fly rod action terms for years. Some of these include very fast, fast, moderately fast, moderate, slow, full flex, mid flex, tip flex, progressive taper, aggressive taper, stiffness, nodal point, matrix, etc. To complicate things, many of these terms have been used in advertising, so much so that sometimes a fly fisher will buy a rod just for the fact that it is advertised having a certain action. Also, with the rise of internet rod outlets and the decline in brick and mortar retail stores, a potential buyer rarely actually lays hands on a rod before buying it. This lack of “hands on data acquisition” makes many potential buyers wary of purchasing a rod in which they don’t know how it feels.

It goes without saying that the best way to evaluate a rod, to see if you like it or not, is to lift it, cast it, and fish it. This of course is not often done for the fore mentioned reason, as well as others. Because of that, many users rely on rod reviews by those that have lifted, casted and fished the rod. Unfortunately, nomenclature is not uniform among reviewers, and by their very nature rod reviews are subjective. How one reviewer casts a rod is different from another. Our hand holds may be different, our body stance and balance point are different, our body height and mass are different, let alone what line is used, what fly is used, what was the speed of the water current, was the wind blowing, etc? All of these parameters, and many others, make a rod feel differently to different users. Therefore, rod reviews are subjective and should be read and interpreted with caution.

In an attempt to help clarify tenkara rod action by making the nomenclature more uniform among users, certain static rod tests have been proposed. I say static, because these tests do not try to communicate how a rod actually feels to a person when fished, but rather, they try to numerically quantitate how a rod might feel as compared to other rods.

The tests must be simple in design, preferably not requiring specialized tools, requiring no complex math formulas, be reproducible and somewhat accurate. They must not be designed to answer the physics of rod action, and must not require an advanced degree to utilize! There are four static rod tests that have been proposed and meet these criteria. These tests include: 10 penny Bend Profile, Common Cents System of rod stiffness, Rod Flex Index, and the rod Rotational Moment (or torque). Let’s look at these tests and see how they might help classify a tenkara rod.

10 Penny Bend Profile

This test is first described and used by tenkara early adopter Chris Stewart, aka, Tenkara Bum. Stewart realized early on that the standard Rod Action Index of 5:5, 6:4, etc was not uniform among tenkara rod manufacturers. Basically, what was one company’s 7:3 was not another company’s 7:3! Therefore he devised a radically simple way of actually seeing the rod’s bend profile.

Stewart took ten US pennies and placed them in a small plastic bag. This bag was in turn attached to the lilian of the rod to be tested. The rod was then angled at a standardized but arbitrary degree of elevation (he put the rod butt in a plastic file box). The bend profile could then be seen very clearly. It was a simple test design, easy to perform, and reproducible. The other neat thing was that multiple rods (each having the same Rod Action Index) could be tested side by side. This showed that rods of the same Index did not always have the same bend profile.

Courtesy of TenkaraBum. Used by permission.

Courtesy of TenkaraBum. Used by permission.

Common Cents System of rod stiffness

This test was initially developed by Dr. William Hanneman and published in RodMaker Magazine in 2005 to test western fly rods. He developed the system to answer the exact same question that tenkara fishers ask about their rods, namely, what makes a 5-weight a 5-weight and why do different 5-weight rods feel different? Of course, in tenkara it would be worded, what makes a 7:3 a 7:3 and why do different 7:3 tenkara rods feel different?

Stewart recognized that a systematic method of measuring stiffness would be valuable, and when researching methods found that the Common Cents System (CCS) could be adapted to measure tenkara rods. This would allow a database of rods to be generated.

Here’s how Stewart describes the test: “Each rod is clamped in a horizontal position and weight in the form of pennies in a light plastic bag is attached to the rod tip. Pennies (specifically, pennies minted after 1996) are added to the bag until the tip bends down from the horizontal by a distance equal to one third of the rod's length. For those of you outside of the US who don't have pennies or a sense for how much they weigh, ten pennies weigh 25 grams.” (from http://www.tenkarabum.com/tenkara-rods.html).

Once again, the CCS test passes our test requirements, being simple to preform, utilizing no specialized tools, reproducible and somewhat accurate. I say somewhat accurate because there will be slight differences in the weight of the plastic bag, and it is very difficult to get the rod exactly horizontal. Still, the test passes muster and has been verified and adopted by many western rod makers as a reliable static test for measuring, and therefore classifying, rod stiffness.

Stewart has used the CCS to generate a database of rods which is extremely useful when researching a rod’s overall stiffness and comparing it to other rods. It may be viewed at http://www.tenkarabum.com/common-cents-database.html.

Rod Flex Index

Although the CCS does give information regarding a rod’s stiffness, and therefore potential action, it does have one major flaw. That flaw is that just like not all 7:3 rods feel the same, not all 15 penny rods feel the same. For instance, a 450 cm rod that has a CCS of 15 pennies will feel and fish much differently than a 240 cm rod of 15 pennies. Yes, they are both 15 penny CCS rods, but the rod length factors into their casting actions. To better classify rods utilizing Chris’s CCS database, it was decided to neutralize rod length by taking the rod’s penny rating and divide it by the rod’s length, in meters. This takes rod length out of the question and gives us the Rod Flex Index (RFI).

When utilizing the RFI, the lower the index number the slower the action, the more full-flex the rod. Conversely, the higher the number the more fast and tip-flex the rod. Using this index will let a tenkara fisher immediately have some idea of how the rod may feel when casting and what other rods he or she may have experience with would compare. Slow or full-flex rods have an RFI of 3-4.5. Moderate or mid-flex rods have an RFI of 4.6-6.5. Fast or tip-flex rods 6.6-8.5, and very fast or minimal-flex 8.6+.

Here is an example of how the RFI may be of benefit to someone wanting to buy a short fixed-line rod to fish small, tightly overgrown creeks (something that most tenkara rods are not designed to do). Let’s say that this person already owns a Tenkara USA (TUSA) Ito, and really likes its dynamic casting action. That person now goes to Chris Stewart’s CCS database and sees that TUSA Ito at 4.5 m is a 15 penny rod. They then see that the Shimotsuke Kiyotaki 24, a short keiryu rod is also a 15 penny rod. They say to themselves, “I really like my Ito’s slow, rich casting action, therefore I’ll buy a Kiyotaki 24 since it, being a 15 penny like the Ito, will have that same slow, rich action”. They couldn’t be more wrong! Using the above RFI formula (15 divided by 4.5), the Ito at 4.5 m has an RFI of 3.3 (slower end of full-flex rods), while the Kiyotaki 24 has an RFI of 6.3 (15 divided by 2.4; faster end of mid-flex rods). The Kiyotaki 24 is a much faster, tip-flex rod while the Ito at 4.5 m is a very slow, full-flex rod, yet they are both 15 penny rods on the CCS. Trust me, I have fished both the Ito and the Kiyotaki 24 and although they are both 15 penny rods they don’t feel or cast similarly!

To summarize, the RFI helps a tenkara fisher compare rod actions to a rod that they may already own or have used. An up to date version of the Rod Flex Index may be seen at the blog Teton Tenkara.

Rotational Moment

The final test is the rotational moment, or torque of a rod. Many tenkara fishers have experienced that as a rod gets longer the more tip heavy it feels. This is a fact of physics. There are a number of complicated formulas to numerically quantitate the tip heaviness and swingweight of a rod, but the easiest way to estimate it is to measure its rotational moment, also called moment of force or torque. This is done by measuring its weight in kilograms and multiplying that by its center of gravity distance in centimeters from the butt of the rod, when the rod is fully extended. Torque = mass times radius. This measurement has been substantiated commercially and is used by Gamakatsu, a high quality Japanese rod maker. They list it for their tenkara, keiryu and seiryu rods. The larger the number, the more tip heavy the rod.

Image from Gamakatsu Multiflex 40 carton.

How rotational moment for a rod is measured and calculated.

Moment can be measured for all fixed line rods, but it mainly comes into play on the longer ones. Rarely is the rotation moment of a 360 cm rod important, but it often times is for a 390 cm one. I personally only measure moment of force or torque on rods 380 cm or longer.

Some rods have very low rotational moment, and thus so feel very lightweight (regardless of their actual weight). Design, materials, taper, etc all play a part in keeping the rotational moment low. The Gamakatsu Ryokei 390, a seiryu rod, has a rotational moment of only 4! That is amazing for a 390 cm rod! For comparison, here are data of a few other rods I have used (rod lengths vary): Oni type I - 5.2, Nissin Air Stage Honryu 380 - 5.3, Shimotsuke Ten - 5.4, Allfishingbuy Hirame-ML-3909 - 6.8, Nissin Royal Stage 400 7:3 - 7, Daiwa LT39SF - 7.1, TUSA Ito - 7.8 at 390 cm, TUSA Ayu II - 8.5, and the TUSA Amago - 10. Any number over 6 and the rod feels tip heavy; the larger the number, the more tip heavy. Likewise, the larger the number also means more stress on your forearm and more chance of microtears being induced in the extensor tendon with repeated use (aka, tennis elbow).


Not to belabor the point, but it does bear repeating: the best way to tell if you are going to like a certain rod is to cast it and fish it. Without doing this you can’t tell what the rod’s characteristics, performance and dynamic action will be like — that is, whether you’ll like it or not. Rod reviews may help somewhat, but let’s face it, casting and fishing a rod gives you much more information than a rod review.

That said, in light of the fact that it’s pretty difficult to cast every rod we are interested in, we often rely on reviews from those who have used the rod. Unfortunately, rod reviews are inherently subjective and words like “smooth”, “light”, “fast”, “sweet” do not communicate the overall experience of casting any given rod. What is “smooth” to some may not be to others.

To combat this, static tests such as the 10 penny Bend Profile, Common Cents System, Rod Flex Index and Rotational Moment provide useful information to aid a person in directing a rod purchase. These tests are not perfect, but when used properly, and their strengths and weaknesses kept in perspective, their results can help quickly narrow the field of potential rods for which you to spend your precious money on! Happy hunting and caveat emptor!

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