Test Curve Measurement in Fishing Rods


Test curve has been used as a measurement of the action of fishing rods for carp and specialist fish since the 1950's Probably the first reference is in Richard Walkers writings on Stillwater Angling. First I am going to explain what test curve means. everybody thinks they know, but nobody seems to be sure when you quiz them. Secondly I will let you know why I think there are problems with this measurement, and finally I will suggest some alternatives. The last part is tough.

(When I wrote the above paragraph I had completely forgotten about earlier references to Test Curve in Hardys Anglers Guides. In front of me now I have a copy of the Hardy's Big Game and Sea Fishing Tackle catalogue from 1937. In this there is a good description of Test Curve, but the Hardy measurement system differs from Dick Walkers.)

What is Test Curve?

Test curve is a guide to rod power and action. It is a function of both, and  it is usually taken to be the weight in pounds and ounces needed to pull the tip of a rod round to 90 degrees to the butt. It is obvious why test curve was adopted. Just like length of a rod, it is handy to have a measurement that can tell you something about the power of a rod. It can be measured in a number of ways, but simplest is to imagine a rod, clamped by its handle in a horizontal position, a few feet off the ground. With line threaded through the rings, you attach a weight close to the tip ring. Start off with 1lb on a rod assumed to be say 2lb test curve. The rod will now bend under the weight, the tip moving lower, and a curve developing throughout the rod. To measure test curve you simply add weight until the tip is at right angles to the butt section. Another option is to use a spring balance to load applied as you increasing the pull at right angles to the butt. So the test curve of the rod equals the weight applied, the load, to bring the tip to 90 degrees from the butt.

(In the original Hardys method, the test curve is the load on the line when the line is a prolongation of the rod, and the pull is from a position that a fighting fish would fight its hardest. How nebulous is that!)

Simple isn't it ? I wish! - It is full of pitfalls.

Problems with test curve.

We can divide the problems into two. There is a problem of measurement, and a problem of interpretation. First the measurement problem....

Let me start with an analogy. If you stretch a cable or rope across a wide gap, say the Avon gorge, however tight you pull the rope or cable, it will never become straight. The weight of the cable or rope causes sag, that cannot be fully removed by tension on the ends. This is to do with the vectors of the forces. In just the same way, you cannot pull a tip to 90 degrees, by a pull on a rod at ninety degrees. You can get close, but not all the way. As you approach ninety degrees, you need bigger and bigger weights to make smaller and smaller changes in tip angle. For measurement to be precise and accurate, we should be making measurments in a way that small load changes make big changes in deflection. This is all wrong headed. Another problem is that there is no standard way of clamping the handle during measurement, and small position changes at the handle can make big differences at the tip. Put simply, the whole concept of measuring test curve is flawed.  We all make different adjustments, fudges if you like, to come up with a figure that is meaningful to anglers, because as a relative measure test curve is is the best indicator of rod power we have just now.

One company I know  works backwards. The old adage was to use one ounce of lead for every pound of test curve. This other company finds the best casting weight, say 3 ounces and then decides that is a 3lb rod. Today however we want our 3lb rods to cast more than that, so that doesn't work well either.

In practice the problem of pulling tips to ninety degrees with a ninety degree pull probably seemed academic with a cane Avon or MkIV carp rod. The test curve method worked in a practical sense for flexible forgiving cane rods. But as rods have got more powerful and materials have changed from cane through glass to carbon, the problems of measurement have increased dramatically. The high modulus tip of the modern rod is more reluctant to follow the line to ninety degrees.

This leads on to the interpretation of test curve problem. Let me give you an example. Charles Ritz, founder of the Ritz hotel, used to like his fly rods very specifically made to his tapers. The last few inches of the tip which some people would favour tapering away at the same taper as the rest of the rod, he liked to have almost parallel, in effect he stiffened the tip to help lift line. If his specific taste had been applied to a modern carp rod, say a Ballista, then it could result in a big change in estimated test curve, as the normal tip tapers away quickly and is relatively eager to follow the line to 90 degrees, whilst the stiffened tip will be more reluctant to bend. However, in practical fishing, the effect of this change would be very small in fish playing ability, or casting.

Another example. For France we make many rods with a slightly more parabolic action than for the UK market. Regrettably we all mean different things by parabolic too, but what I mean is rod that is somewhere between fast taper and through action, so a French rod might be slightly less tippy than a UK rod.. A parabolic rod that is suitable for three ounce casting, will measure at a higher test curve than a rod that is fast taper of equivalent casting power. Again, it is to do with how willing the tip is to follow the line around to ninety degrees.

The test curve concept is flawed!

In the past, I have discussed this problem with many people, but so far none have come up with a solution. What we need is a measure of how much line a rod gives during flexing as a result of a pull by a fish. Imagine a rod clamped in a fixed position so that we could measure deflection against force of pull. If we were to plot on a graph the amount of line given , or deflection of a rod, against pull or load, we would get a curve. This curve would vary from rod to rod according to the action. If we can find a simple way to describe this curve, then we would have a measure that indicated both power and action. The curve of deflection against load would have a faster rate of change, a steeper ramping up, than a through action rod which would be closer to a straight line.


I have had some correspondance from Bernard Sunderland who has drawn attention to some other ideas including a 45 degree deflection method published by Australian writer Dick Lewers 'How to build a fishing rod' by Dick Lewers, 1981 David & Charles Publishers Ltd

To date I have not come across an existing measurement of rods that works for rods of widely differing action and type. The ideal measurement would also take into account feel, which is a function of several factors including balance point and damping .Two rods of the same power can feel quite different because of blank weight or fibre modulus or the weight of the rings used. For carp rod comparison here in the factory we use a measure of defection from the horizontal of the rod tip with a load of 1 kilogram. A similar idea works well for fly rods but with a smaller load. It is not perfect, but it means more in real terms than test curve. 

So there we are....test curve is a flawed measurement, but for the moment anglers see it as the least worst measurement so we continue to put it on rods.