A rudimentary method for measuring rod stiffness

[HarveysMinnow]

As we can surmise from the prevailing opinions in a recent thread on rod fatigue (or the lack of it), our fishing rods should last a lifetime, as long as we protect them from various forms of abuse. Also, it was asserted by several members that ‘rod stiffness’ or ‘flex resistance’ is not likely to change noticably over years of use.

If these opinions hold true, why bother to measure anything? Well, perhaps there’s a couple other facets of this topic for which some numerical values might be of some benefit to us:

Let’s say we wanted to compare the flexibility or stiffness of two or more of our existing rods. We could do this ‘by feel’ or ‘by sight’ perhaps, but other than subsequently saying one rod is stiffer than the other, we would not have much to hang our hats on. For some folks, that’s enough – they don’t care about any numbers – they just want to catch Bass, and I can’t fault them one bit for that. Others sometimes want to know more, and for those of us who fit that category, or those who just like to tinker with things, it’s sometimes a challenge to figure a way to obtain a number that will mean something. (If nothing else, it’s something to do when it’s just too danged hot to fish.)

Another instance where a ‘flex number’ might be helpful is when we go out to purchase a new rod. Maybe we would like it to be as close as possible to the same stiffness of one of our existing rods. Or maybe we would like to see if comparable rods of different brands are similar in stiffness. Whatever the case, some of us just like to derive our own numbers.

Fishing scales – the type with a digital readout – contain a cheap but functional version of a strain gauge. Not only can these scales weigh Bass, they can also be used to set reel drags to a certain percentage of the line breaking strength. Along these same lines, they could be used to obtain a relative value for the flex resistance of a fishing rod. [When I say ‘relative value’, I just mean that the readings we make don’t relate directly to any standard. We have no way of knowing whether the strain gauge in one unit is calibrated the same as in another unit. Hopefully, they would be close, but unless someone wanted to purchase several of them and test their uniformity, we just won’t know for sure.] This means that one person’s readings could vary from another’s, even on the same brand and model of rod.

In order to make a measurement on a particular rod, we will need some way to secure the handle end, so that we can pull the rod tip across an arc that approximates the range of flex that the rod may experience when a fish is hooked. We can decide on a suitable degree of bending by visual experimentation, but first let’s look at the rod holder.

As you can see in the photo at the end, my rod holder was constructed so that it can be anchored to one of the legs of my workbench, using a sturdy woodworking clamp. The base of the rod is inserted into the 1-1/8 “ hole. The rod also rests against an adjustable block, which can be positioned in the general area of the reel mount (with the reel removed). The resting point where the rod fits against this block becomes the lower end of the flex curve when the rod tip is pulled horizontally. For the setup in the photo, I would pull the rod tip to the right.

To make the actual measurement, you will need one of the digital fish scales mentioned above. Cabelas sells one made by Rapala which has a 0 – 15 lb range and reads in pounds and ounces. Also available, from a company called “Micromark”, is a similar but more sensitive device designed to measure drawbar pull of model railroad locomotives. It’s range is 0 – 176 ounces (11 lb) and it reads to the nearest tenth of an ounce. Just hook your measurement unit onto the rod tip and pull against the block to some arbitrary point where the rod tip is horizontal (or to whatever point you believe is appropriate). You may want to mark this spot, if you want to compare your readings for two or more rods of the same length. (Also, if you are into statistics, you may choose to take several separate readings on the same rod and average them.) Whatever the case, it’s important to pull the rod(s) tips to the same point for each reading, otherwise the numbers will be meaningless.

Some typical values:

Since most of my rods are of the ultralight to medium action variety, I opted for the more sensitive unit mentioned above. Consequently, my values are in ounces, and they are the average of three reps for each rod.

Shakespeare micro-graphite 5’ UL spinner 13.7 oz

Shimano VTS 5.5’ L spinner 13.3 oz

Shimano Sojourne 60M2 6.0’ M spinner 25.1 oz

Diawa Strikeforce (no1) 6.0’ M spinner 21.9 oz
(Two identical rods)
Diawa Strikeforce (no2) 6.0’ M spinner 19.5 oz

Gander Mtn X-factor 6.5’ BC 38.4oz

Field & Stream (IM-6) 6.5” BC 39.6 oz


Now that I’ve done all this, I’m not sure what I’ve learned, if anything. I guess I expected the two bait caster rods to yield higher numbers than they did, based on the way they feel. Other than that, no major surprises from my point of view. I believe the two Diawa rods are virtually the same, within the limits of experimental error. So, I invite comments, critiques, questions, and opinions from you gentlemen. I realize this is a long and involved posting, so I thank you for your time & indulgence.


Safety Considerations: If you decide to try this at home, be careful you don’t whack yourself or someone else in the face by releasing the rod tip abruptly. A flexed fishing rod can hold considerable stored energy, so return the rod to its unflexed vertical position before unhooking the measuring device.

Disclaimer: (This forum member assumes no responsibility for damage to equipment or personal injuries incurred while following this procedure.)

On a lighter note and in view of remarks made in other threads, I fully suspect that someone will decide to wise off about this. So allow me re-emphasize that we’re talking fishing rods here, and that attempting to use this method to measure stiffness of your personal anatomy is not recommended.


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