Power is one of the most talked about, and most misunderstood, characteristics on a blank technical data sheet.
Every blank we design and produce at Composite Forge ships with a TDS that lists three related values: Power, P100, and T15. In this second walkthrough of CF Engine, we’re breaking down what these numbers actually mean, how they’re calculated, and how they connect directly to the way a blank bends.
Watch the full CF Engine walkthrough on Power, P100, and T15.
Every Rod Forge blank lists its own TDS, including the Power, P100, and T15 values covered below.
What the TDS Power Values Actually Represent
Every Composite Forge TDS includes three metrics that describe power: Power, P100, and T15. These three values are calculated using the same underlying method, but each one is evaluated over a different length of the blank. Understanding why we split power into three separate readings starts with understanding the graph they come from: flexural rigidity.
Flexural Rigidity: Stiffness Along the Length of the Blank
In CF Engine, a flexural rigidity graph shows the stiffness of a blank per unit length, plotted from the butt end on one side to the tip on the other. As expected, flexural rigidity is highest at the butt, where the blank is stiffest, and drops off sharply toward the tip, where the blank is thin and flexible.
That taper is not incidental. If a blank held the same flexural rigidity value from butt to tip, it would perform essentially like a constant diameter tube, and performance would suffer. A well designed blank needs different stiffness values at different points along its length, because the butt and the tip serve entirely different roles in how the rod loads and unloads.
From a Full Profile to a Single Power Number
The challenge is that a flexural rigidity graph is a full profile, not a single number. To describe a blank simply, in a way that can be compared across a full lineup, that profile needs to be condensed. Power, P100, and T15 are essentially averages of the flexural rigidity profile that also account for where along the blank each value falls.
Here’s how each one is evaluated:
- Power is calculated over the first third of the blank’s length, from the butt forward.
- P100 is calculated over the entire length of the blank.
- T15 is calculated over the last 15 percent of the blank, at the tip.
Power is treated as the primary metric because the first third of the blank is where the heavy lifting happens. P100, while it captures the whole blank, starts to blend in with action, since the remainder of the blank beyond the first third is where action gets shaped. That makes P100 more of a secondary reference for power rather than the primary read. T15 isn’t a power metric at all. It’s a performance metric focused entirely on the tip, and it plays a larger role in how we describe action, a topic we’ll cover in a future video.
A full TDS report for the HTD-70MM blank, with Power calculated at 14,213.6 lbf in² and rated Light for this blank.
Connecting Power Metrics to Deflection
F Engine also displays deflection profiles alongside flexural rigidity graphs, and the relationship between the two is direct. Take a series of blanks ranked by power: the highest power blank sits at the top with the least deflection, and the lowest power blank sits at the bottom with the most deflection, under the same load case.
That ordering holds because the flexural rigidity profiles across a well built series are essentially offsets of one another, almost like consistent step ups from one blank to the next. When flexural rigidity increases, deflection decreases in that same order, every time. This is what lets us say the power metrics objectively define the power level of a blank, rather than relying on feel alone.
From a Number to a Power Rating
Every blank’s calculated power value slots into a defined range that corresponds to a power category, whether that’s medium light, medium heavy, extra heavy, or another rating along that scale. For example, one of our recent TDS sheets showed a power value of 35,883.4 square inches. Fit into our power rating ranges, that number placed the blank objectively as a medium heavy.
That objectivity is the real point of the exercise. Power ratings have historically been somewhat subjective, varying from one designer’s interpretation to the next. By calculating power directly from measured flexural rigidity data, CF Engine removes that ambiguity and lets us define, and compare, power consistently across every blank we produce.
What’s Next: Action
Power is only part of how a blank performs. The next installment in this series moves into action, a set of metrics that can be measured directly from a physically deflected blank and compared granularly, not just by broad power category. Look out for that walkthrough soon.
