I just got a 45# 52" recurve that feels like a kid's bow at the beginning of the draw and VERY quickly gets up to weight at the end of the draw.

My ILF Bow is about 45# with long carbon foam limbs. It has a good bit of tension right at the beginning of the draw and builds up very steadily throughout the draw.

Common sense says that the steady increase of force = a steadier release of force.

Is it true? Is that why some bows seem 'twitchy'?

ALSO...my 52" bow is unusually quiet and smooth for a short bow. I think that the lack of resistance is acting as a shock absorber.

A bow that is slow to add poundage - up until it begins to stack, anyway - will have poorer cast than a bow with high "preload" that starts adding resistance very quickly as the spring comes back.

I could probably explain it better if I had not been such a miserable student of calculus, but basically....

The area underneath the draw force curve represents the energy stored in the limbs of the bow. Think about a very hard cam on a compound: the force curve goes from zero to it's max in the first couple of inches and stays at that maximum value until the cam rolls over and you hit the let-off. The "curve" is practically a square. And compared to a bow which has a "curve" that is really a line at a 45° angle, the hard cam stores about twice as much energy. So if you have a force curve that stays very low most of the way back and then jumps up to its maximum at the very end, it will store very little energy.

And then as to the manner in which that energy is released… When a bow stacks, it has high load on the limbs for only a very short period of time... and because the energy comes back out in the same manner that it went in, you really end up with a very short power stroke. Effectively, you have just shortened your draw.

And that's no good.

There's some. I'll have to unstring it and take a pic. It's a Pearson Hunter II. I have seen it referred to as a semi recurve

GF, That makes sense. I bought it as a short range bush bow and it seems fine for that. I guess the good news is that I can hold partial draw for a long time :)

The fd curve stored energy is only half of whats going on the other half is how much of that energy the bow is capable of putting into the arrow. I've seen recurves storing over 100% of the draw weight but only put less than 75% of that into the arrow. Then you feel and hear the rest of that energy being disapated by the limbs

I have a bad habit of varying my DL, especially when shooting longer shots. A bow that stores most of it's energy in the last couple inches is much less forgiving to draw length variations.

JSD -

In my experience: A bow with a lot of initial preload, will require a stiffer arrow and "may" be marginally faster that one that loads up farther back on the draw.

Viper out.

That all makes sense.

It has a very useful 30 yard point on....but you CANT SAHORT DRAW

What you are describing is symptomatic of a bow built with limbs that are too soft in the inner limbs. IOW, the inner limbs bend too much early in the draw. That means the outer limbs are traveling to the rear and the string angle is growing too fast. When the bow suddenly becomes harder to draw it's an indication that you are approaching, then eventually at and possibly exceeding 90 degrees of string angle. Draw weight at high string angle is not contributing your energy to casting the arrow. If you create an actual FD curve for your bow you will see, per the explanation in the previous post, that there is a drastic reduction in the area under the curve at the end of the draw. You may be drawing more weight at that point but it's not giving that energy to the arrow.

When you release, those same weak inner limbs now have to propel the outer limbs which are not doing much work but still need to be returned to their position at brace. That work is falling to the already weak inner limbs.

It's kinda like a bicycle built for two where both Passengers are rotating their pedals but one is applying muscle to the rotation and the other is simply following the pedals.

Pre-load = continued acceleration. Not such a violent kick it the rear at the beginning. Ken

Pre-load has more weight on the string at rest so has more weight at the beginning of the draw. I have shot bows that were way too mushy at first and got all their weight in the last few inches. they tend to be slow. I've also shot bows that had very little preload but started adding weight fast at the draw and were pretty even in draw curve all the way out. The best shooting bows I ever had were brackenburys which were the last ones I described. They were a tiny bit slower(4 or 5 fps) but for whatever reasons they hit with my other bows out to about 25 yards but hit higher than my others past that. An old timer told me that was because the bows with too much preload put so much vibration into the arrow that it slows down faster. I dunno about all that but they sure shot more accurately than any others for me at distance once I got used to them shooting higher. I wish now I would have chrono'd them at 30 yards and compared them to high preload bows.

Just for the sake of novelty, I will answer the actual questions asked:

" Is it true? Is that why some bows seem 'twitchy'?"

Depends on which is the "that" You seem to be suggesting the bows with less early energy under the F/D curve (EEUFDC) will be perceived as twitchy, and as someone mentioned that is a characteristic of string follow bows that are nor perceived as twitchy. The majority of ILF limbs max out at lower levels of energy under the F/D curve compared to what most archers know you can have. Which is why there are certain brands like Uhhka, that are regarded as extra fast, but twitchy/harder to shoot/unstable. Even in the compound world, round wheel bows or similar non-square wave cams, are preferred for their stability, or shootability.

Of course EEUFDC and more energy are not the same thing, but with sticks they come close. The only thing you know in making meaningful comparisons is that the draw weights are the same at full draw. Most curves on sticks are pretty linear, so the most likely place to beef up the F/D curve is early.

"ALSO...my 52" bow is unusually quiet and smooth for a short bow. I think that the lack of resistance is acting as a shock absorber."

Well less energy in is less energy to deal with on the out so it should be quieter. While early preload probably makes it easier for the string to keep pushing, early unload catches the arrow while it is stationary, and then eases off when there is a lessor chance of effective energy transfer. Think of slaming a door with all you energy transferred in the early part of closing, the air drag will ensure that the door slams less hard than if you moved it a bit at first, then really belt it home to the frame at last, same energy overall.

All that said, there are very different dynamics in short bows, and less limb weight to deal with relatively speaking, short bows with normally a lot of delta are like Matthews compounds where the limbs are so parallel the bows don't jump forward, except in the case of small stick bows it is a lot less pronounced. And there are at least two other things they do that have an effect.

The bow that catches me off track is one that has more variation in cast with slight draw length or release energy variations. I had a recurve, target riser with short limbs, that with a half inch added to the draw jumped the speed way up, but that same bow with a half inch short draw, creeping with long holding times, changed the cast downward dramatically. I shot that bow with sights, so the difference was very evident. I added a clicker to control my draw length. My favorite bows tend to forgive that release variation to a degree, regardless of how they build the power lines. Norb Mullaney tried to explain that to me once, it had something to do with static hysteresis which created a limb inefficiency that did not gain as much power because of added hysteresis with the longer draw, but was more efficient with less hysteresis at the lesser draw, which to a young kid, sounded like a foreign language at the time.

Bows that stack are very touchy about draw length. You have alot of the draw weight of the bow in the last couple inches so if you short or long draw a half inch it can make 3,4, or even 5 lbs difference in bow weight.

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