Fly rods are essentially springs. Their purpose is to store and release energy. Action is just the spring constant. In Physics, that tells us how stiff a spring is, and how much force is required to compress it. It also tells us how "fast" the spring will decompress when we release the compressive forces on it. Maybe that's why they use the "fast" and "slow" nomenclature to describe rod action. In the context of fly fishing, action effectively tells us how fast the rod will release energy (as it unloads) and also how easily it will store energy (as it loads). Thus, a slow action rod easily compresses and stores energy and is slower to decompress and release energy (less line speed). Which is why they have a better "feel" and are more forgiving. A fast rod is harder to compress and store energy and is faster to decompress and release that energy (generates more like speed).

Good job Ben like always , thank you.

Very good explanation thank you

I like fast for meatier flies...easy to pick back up and relaunch it fast.

Great video

For night fishing you ideally need a medium/slow action rod as you are relying on feel on your casting stroke.

Slow is best for everything.

Hi, your explanations are absolutely excellent. The best i seen so far on KZfaq. I own a 9ft #9 rod for pike fly fishing. Way to long and heavy for the environments I'm fishing in (Dutch "polders" with lot of trees nearby and often very windy. So I'm looking for a 7.5 ft #7 or #8 for example (or even a 6.0 ft #7), and in two pieces. Nowhere to find on the planet. So I'm considering to build one myself.

Every fast action rod is actually a weight over, so if you looking for a 8wt get a 7wt fast action.

So if your only criteria for rod selection is " needle point, ultra tight loops " .....your best selection for action and length is.....??

I’ve just bought a hardy wraith 10ft 7wt half price. I need help finding lines that will suit. I’m after a float intermediate and sinking and I’m trying to find out what will match this better? I’ll be fishing for trout on Stillwater. And also be wading into some of the Stillwater’s. Any help or suggestions will be greatly appreciated.

The most important factor about fast vs slow rods is how heavy , a fast rods are always lighter than slow rods and is the most important factor cause everything else falls behind the weight of the rod, a bvk fast rods 2.8 ounces is way much difference than a 4 ounces glass rod specially if you are a small guy like me, 5 ,4 think about it😢

You have, Ben; so I won’t be calling. 😉