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THERE'S MAGIC IN THOSE CAMS! ![]() STORED ENERGY (UNDER THE CURVE)` On the two graphs, notice the shaded area under the green line. This area represents STORED ENERGY. That's an important term - remember it. As you draw a bow, you're really just transferring energy from your body into the limbs of the bow. The gray area under the green line represents how much of your muscle energy is being stored by the bow. The more energy you can transfer into the bow, the more energy is available to transfer into the arrow when you shoot. Though both bows hit the same peak weight, the traditional bow doesn't come up to weight until you get it drawn most of the way back. So during the first half of the drawstroke, you're not storing up much energy. Even worse, the traditional bow becomes toughest right when you could most use some relief (when you're trying to aim and fire). All full draw, the traditional bow is at maximum weight. So once you get your traditional bow drawn back, you can't dilly-dally around. You have to shoot quickly - unless you have Herculean strength. The compound bow fixes both of these fundamental problems, thanks to the magic in the those cams. The compound bow not only stores more energy by manipulating the forces, but it "lets-off" (partially relaxes) at the end of the drawstroke, so you're holding less weight at full draw, allowing you more time at to aim and fire. Brilliant! But none of that is possible without the mechanology of the cam. Manipulating a bow's draw weight, and thus the energy storage graph (called a force draw curve) takes some clever Calculus. Fortunately, that is literally the specialty of our industry. You want more for less? Well here it comes. Get ready to be amazed. |
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IT'S ALL ABOUT THE CURVE` THE FORCE IS WITH YOU` By mechanically manipulating the draw weight, the compound bow can literally change that straight line into a heavenly mountain of energy storage - a humpy little volcano of arrow velocity. With a cam, the drawstroke can be directly manipulated such that the bow's draw weight rises to peak weight much sooner in the cycle. But the cam can also "flatten out" the energy storage curve, to maximize energy storage along every inch. This greatly improves the area under the curve, and thus the storage/output capacity of the bow. So compound bows are faster than traditional bows - a LOT faster. Again, the area under the curve is the real secret sauce of the compound bow, and the size and shape of that flattened bell-curve will have everything to do with how the bow feels and performs. CAM PROFILING` Here's where it gets fun. A compound bow doesn't get its shooting characteristics by accident; a bow doesn't just "come out" one way or another. The shooting characteristics are engineered into the bow from conception. On the drawing board, the shape of that force draw curve can be manipulated any way we like - depending on how we want a bow to feel and perform. The actual geometry of the cam system determines how soft or aggressive the powerstroke will be. This is called the cam's profile. Sometimes we hear people say cam grind, of course, cams are machined, not ground, but you get the idea. Aggressive cams yield a flatter boxy looking force draw curve, smoother cams yield a traditional bell-shaped graph. Look at the sample graphs below, taken from three different cam profiles. Pay special attention to the shaded areas. That represents energy storage. The more shaded area, the faster the bow shoots. But to get that extra energy storage, the cam profile must be more aggressive, with more abrupt transitions. All too often we hear bow companies tout their bows as both fast and smooth - when it's far more accurate to say fast OR smooth. When it comes to cam profiles, you can't have your cake and eat it too. But many consumers have been brainwashed into believing they can. ![]() NO FREE LUNCH` So where does the modern compound bow get all its power and ferocity? From technology? From force multiplying cams? Nope. Just like every other hand-drawn weapon in human history, the compound bow still gets ALL of its energy only from you. We mention this again because cams which optimize energy storage do so exclusively at your expense. The bow is only the tool. You still have to supply the power. Nevertheless, cams are often marketed like race car engines - revved up with 20% more power and ripping through the competition. The "power" of the cam is practically implied to be internal - but it isn't. It's easy for customers to lose sight of how difficult it will be to pull 70 pounds across a 20+ inch optimized hard-cam powerstroke. If you grew up on old wheel style bows (think Bear Whitetail), a modern hard-cam bow might be a shock to your machismo. If you choose a hot IBO Speed bow (340+), you better eat your Wheaties. They are no joke to pull back. One of the most common customer service calls we get is about reducing a new bow's draw weight. So it's worth saying one more time. Most guys bite off more than they can chew. If you're going for the Super-Annihilator 9000 model with the 350 fps IBO Speed, you better be ready. That speed won't come free, even if the bow's manufacturer tells you it's buttery smooth. You still have to muster the muscle to earn every fps. ![]() |
![]() THIS DOESN'T HAVE TO BE ENIGMATIC` As a technical matter of measuring how aggressive a cam really is, we could simply publish the total ft-lbs represented by that shaded area under the curve. It's quite easy to measure (and all the manufacturers already have this data). If customers could tell exactly how many ft-lbs of grunt the bow required to draw back, we could all dispense with the subjective gibberish about draw-cycle smoothness. And if that data were collected and published at a standardized setting, say at IBO test regs (70# peak draw weight & 30" draw length), then consumers could simply compare the numbers. We would expect bows requiring more total ft-lbs to be tougher to draw; bows which stored fewer ft-lbs would be easier to draw. Easy! It would not only make the world a better place for bow buyers, but it would save us from having to use words like velvety and silky when we're at work. EFFICIENCY OF ENERGY-IN TO ENERGY-OUT` Better yet, we could then compare the bow's published output (IBO Speed) to the input, and using a simple mathematical KE calculation we could determine each bow's total efficiency. This would tell us a lot about how much noise and vibration the bow would likely generate. In an ideal world, a bow should convert 100% of its stored energy into the arrow, for a perfect efficiency rating of 100%. If all the energy were successfully transferred into the arrow, there would be no energy left to create noise, vibration, etc. That's an ideal world. In the real world, bows manage much lower efficiencies. You can think of it like this. If a bow requires 90 total ft-lbs to draw, but only manages to successfully transfer 75 ft-lbs into the arrow, then 15 ft-lbs is being wasted somewhere. Of course, energy doesn't just disappear. That lost 15 ft-lbs would represent friction, heat, vibration, noise and other unwanted forces. So the higher the efficiency rating, the quieter and more shock-free a bow would likely be. If this data were to be part of every bow's published specifications, it would give consumers a good way to gauge the overall engineering quality and general performance expectations of any particular bow. So why don't we do this? Because all bows are idealized products, remember? Every bow is ferocious and blazing fast while being incredibly smooth and forgiving, remember? Manufacturers don't necessarily want to provide consumers with a good way to gauge the overall engineering quality and performance of their bows. It's better if we just tell you it's great, and you go along with it. |
CAM TYPES THE FINAL FOUR` Modern compound bows generally come with one of four different types - or styles - of cam systems (Single, Hybrid, Binary, or Twin). While they all accomplish a similar mechanical goal, they each have a unique set of attributes and respective advantages and disadvantages. While the technical subtleties and respective merits of the various cam systems could be debated in perpetuity, in the real world there is an obvious performance parity among them all - especially now that string fiber technology has improved. This isn't to say all cam systems perform exactly the same. They certainly don't. But to claim one cam style really offers a dominant field-advantage over another would be a stretch. ![]() ![]() ![]() ![]() ![]() |
LET-OFF & PEACE IN THE VALLEY ![]() WHAT IS LET-OFF? In addition to controlling the aggression (and energy storage potential) of the drawstroke, cams also control the bow's let-off. Let-off is the mechanical relaxation of string tension at full draw. That means when you come to full draw, the amount of effort required to hold the bow back is reduced (compared to the peak draw weight). The amount of let-off a bow achieves is properly expressed as a percent of the peak weight. So if a bow has a 60 pound peak draw weight and 50% let-off, it would require only 30 pounds of pressure to hold at full draw. Easy enough! ANOTHER OLD DEBATE` Bowhunting purists used to push-back on the issue of let-off. At one time, it was thought, a "high let-off" bow offered too much advantage to the bowhunter. Many states had laws regulating how much let-off a compound bow could achieve to be a legal hunting weapon. This touched off a long and tiring debate about what percentage of relaxation was acceptable. We bickered. We lobbied. We even argued about the measurement methodology (actual vs. effective) and we made customers endure lectures about hysteresis and the exclusionary rules of the Pope & Young Club. The discussion and technical chase went on for decades, but it all somehow fizzled-out once the cam wars ended. One by one, states dissolved their let-off rules. Clubs and organizations stopped caring about it, and the entire issue of let-off ceased to be a controversy. To this day, we still have drawers full of old 65% cam modules - relics of the cam wars and the let-off debate. 80% OR 80% LET-OFF? You won't be surprised to hear how buying trends and manufacturing parity have largely ended the era of the low let-off hunting bow. The moral of the story is, mainstream buyers like high let-off bows. That's where most of the money is spent? So bow manufacturers give buyers what they want - 80% let-off - and the corresponding politics have followed the money. Today, the overwhelming majority of compound hunting bows are high let-off (75% or 80%). Many manufacturers have entirely stopped offering the 65% option (or a low let-off option is only achievable with a short-set draw stop peg). There are a few speed-bows on the market which advertise 70% let-off, but that's about as low as you'll see. If you purchase a new compound bow, it's going to be a high let-off bow. We realize this doesn't make everyone happy. There are still some technical arguments to support lower let-offs, but all things considered, high let-off bows are decidedly more comfortable to shoot and that's what most people want to buy. For most bow manufacturers, it just isn't worth it to engineer low let-off options any more. So your choice here is usually pretty easy ... 80% or 80%? ![]() |
SOLID AND SPLIT LIMBS` ![]() TRAITORS AND HYPOCRITES` A few years later, the limb failures started to decline. Sometimes we would go weeks at a time without fixing a freshly exploded bow. We started to feel like the Maytag Man. It seemed that limb materials, technologies, techniques and fibers were simply getting better. And as the limbs got better, the limb war somehow quieted. As a matter of limb durability anyway, the point was becoming moot - one wasn't appreciably better than the other. To be fair, we're not suggesting limb failures no longer exist. Now and then a manufacturer still manages to cause a stink with their limb experiments, but the systemic issues have resolved. And today, there just isn't a good argument to declare one style of compound bow limb superior to the other. That reality was soon solidified when many of those same lecturing manufacturers crossed their own lines in the sand, and changed some, or all, of their bows to split from solid, or to solid from split. Most manufacturers now use a mix of solid and split limb styles and make the choice based on logical application, and little to nothing is said about limb style choice in today's publications. Until someone tries a triple limb - or perhaps a Limb & 1/2 - we'll just have to let this old battle go. Strangely, customers seem to have largely abandoned their limb prejudices too. We get very few questions about split vs. solid limbs today. |
LIMB TRENDS ![]() LIMB BIASING` Split limbs may also be getting more action these days because of the popularity of yokeless cam systems (no split-buss cable/y-cable). When a bow's cables are pulled to the side by the cable slide or roller guard, this causes some torque at the cams resulting in cam lean - particularly on the top cam. This normally isn't a problem if the bow has a split-yoke. One side of the yoke can simply be twisted up to shorten it a little and equalize the imbalance. But since many bows now feature (binary-style) cams without split yokes, cam lean is more problematic. Of course, small amounts of cam lean are technically inconsequential. However, the appearance of that leaning cam drives customers bananas. Customers assume its a defect - and blame every miss and burp the bow makes on the cam lean. So manufacturers came up with a smart solution - limb biasing - which is pretty easy to do if the bow features split limbs. The concept of limb biasing is pretty simple: just make one limb a little stronger. Easy! To get those cams to stand upright and to offset the cable tension torque, manufacturers simply install a slightly stiffer limb on the outside of the bow (opposite the cable slide). So, many split limb bows actually have left and right side limbs with slightly different deflections (strengths). We're not sure how wise that is with regards to accuracy. Logic would seem to suggest that two limbs working in unison would be more effective than two deliberately imbalanced limbs, but perhaps the biased limb simply corrects an inherent flaw in compound bow design. The biased limb might actually keep things in better balance throughout the entire cycle. So maybe it really is better. But whether it is or isn't, as long as the technique keeps customers from trying to analyze their bows with a carpenter's square, it's surely a welcome solution. |
PARALLEL LIMBS ![]() GOING A LITTLE TOO FAR` The parallel limb revolution was a great boon for the archery industry. Every non-parallel-limb bow was suddenly obsolete and headed for a garage sale. No self-respecting bowhunter could be seen with an old D-bow. We all needed new parallel-limb bows. So naturally, every bow company scrambled to get a piece of the action. But in every crowd, there's always somebody out there willing to take a good thing too far. The idea of the parallel limb is to get the limbs moving at angles perpendicular to the riser, allowing the upper and lower limb assemblies to cancel each other's inertia. Unfortunately, the quest for sustained sales growth drove a few bow manufacturers to molest the concept. Some tried the more is more method with their limb angles, assuming that if customers liked parallel limbs, they would really like super-duper way beyond parallel ridiculous limb angles - resulting in limbs which were practically pointing straight back at shooter's faces. Ah! There's always that one guy, isn't there? YOU'LL LIKE IT` Here's all you really need to know. Your new bow is going to have parallel limbs, and it should feel dead as a stick when you shoot it. You'll like it. It won't jump. It won't kick. It won't have enough hand-shock to even mention, and if it does, the bow is malfunctioning. Call us and we'll get the bow back for diagnostics and service. Parallel limb bows are basically shock and recoil free. They're supposed to be. Bow manufacturers have been tweaking-around on this innovation for fifteen years. If a new bow has any significant hand-shock today, the bow is junk - end of discussion - no sale! We don't even stock a bow with recoil issues. Call it a "settled science" if you like, but recoil is no longer acceptable - at any price point. And it's all thanks to the innovation we know as parallel limbs, but you don't have to say it out loud. All TV's are flat-screens now. |
THE NEXT REVOLUTION FEELING A BIT SALTY` The truth is, the bow industry is becoming victimized by its own success. In the 90's, the compound bow market was revolutionized by centershot cutaway risers and the new single-cam phenomenon. So everyone needed a new bow (good for business). The next decade we got computer optimized drawstrokes and parallel limbs. So everyone needed a new bow again (good for business). But our market has seen a strange lull the last few seasons (bad for business). There just doesn't seem to be a good reason to replace all of our compound bows again. The technologies and specs really haven't changed enough to warrant sending another generation of compound bows to the garage sale. Many of the new bows on the market today aren't significantly better than bows from five years ago. We submit the technologies and manufacturing processes have simply matured, and that makes us both happy and sad. The sales boon of the parallel limb bow revolution may never come again. The days where customers swamped the pro-shop for the latest cam technologies or limb designs may be over. Until there's a new reason to scrap an entire generation of compound bows, buyers will surely hang onto their existing bows. We don't blame them. The modern compound bow is truly fantastic. If you have one already, enjoy it. If you're a new buyer, you can take some comfort in knowing that your new compound bow isn't likely to be rendered obsolete any time soon. We suggest you buy a bow you really like - and plan to keep it for a while. |
Compound Bow Selection & Research Guide | Chapter 4 |
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