Are you considering investing in a carp rod? If so, you will probably have been looking at a few different models. One of the attributes that you will see mentioned for each rod is the test curve. But what is it exactly?
An Angular Question
Put simply, test curve is the weight required to bring the tip of the rod to a 90-degree angle to the butt while the butt is held horizontally. Imagine a rod clamped into a horizontal position by its handle. If you attach a weight close to the tip ring, the rod will begin to curve.
The heavier the weight, the more the rod will flex. The weight needed to cause the rod to bend to 90 degrees is the test curve. Test curve is the measurement which has been used to assess the action of carp rods since the 1950s. It does give you a reasonable idea of the rod's power but it does have its pitfalls.
Fishing for Answers
The test curve measurement seems straightforward enough, but it is actually inherently inaccurate. The principle issue is physics because the rate of flex does not increase evenly. The closer the curve gets to 90 degrees, the greater the weight required to increase it. Initially, small increases in weight will cause big changes in the angle but later in the process, big weights cause small changes. Nonetheless test curve remains the most accurate way to assess rods as nobody has come up with a better system just yet!
Test curve was a suitably accurate measurement with cane rods which tended to bend uniformly along the shaft. But these days rods are made from advanced technical materials. These tend to be much more powerful in relation to their test curve. The high modulus tips of modern rods are more reluctant to follow the line to ninety degrees. Test curve tells you the weight required to pull the tip of the rod down to 90 degrees but the entire rod doesn't necessarily bend uniformly.
You could see two rods with the same test curve measurement which turn out to have very different actions. One could suit you, the other not so much! What anglers would benefit from most is a form of measurement which indicates both power and action, not to mention feel, but so far this has proved to be beyond the wit of man or perhaps nobody had tried enough!