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The Bowhunter's Pro-Shop
The Big Read for Prospective Bow Buyers (Page 4)

  1. Introduction
  2. Price vs. Performance
  3. Bow Classes
  4. Cam Tech
  5. Cam Specs & Brace Height
  6. Limb Designs
  7. Bow Fitment

three decorative linesDRAW FORCE CURVES & CAM TECHNOLOGY


traditional bow draw force curveWHAT DO CAMS DO EXACTLY?:
How can one bow be capable of 340 fps, while another only shoots 310 fps? Well, before we dive into the differences between the various cam grinds, let's cover the basics on what makes a compound bow a compound bow ... cams. What do cams do? In a nutshell, a cam serves the function of mechanically manipulating the draw weight of the bow at any given point along the draw length. A traditional longbow or recurve bow can't do that. A traditional bow really isn't so different from a simple slingshot. The further you pull back, the harder it gets. Take a look at the sample graph at the right - this is a traditional bow (oversimplified for illustration). It's very easy to understand, as draw length increases, so does draw draw weight. The relationship of draw length to draw weight is linear.

STORED ENERGY: Now, before we go on to compounds, notice the shaded area under the green line. This area represents STORED ENERGY. If you drew back a traditional bow with a draw force curve similar to the graph above, the gray area would represent how much of your muscle energy the bow could store-up and then transfer into the arrow. Here's what the speed game is all about - energy storage. The more gray area you make - the more energy you store - the more speed you get.

COMPOUND BOWS HAVE CURVES: The cams of the compound bow give it two distinct advantages over the simple traditional bow. First, 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 velocity. With a cam, the drawstroke can be manipulated such that the bow's draw weight rises to peak weight much more quickly during the cycle. 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. Plus, compound bows offer the added benefit of let-off (a relaxation of string tension at full draw). Here's how it looks on the same type of graph.

draw force curveLEARN "THE CURVE":
Take a look at the graph on the right. This graph represents drawing-back a compound bow and then letting it back down. Length (distance) is plotted against weight. At marker (1) the bow is at rest. At marker (2) the bow has been drawn back about 4 inches and the draw weight has increased to roughly 40 lbs. As the shooter continues to draw back, the weight gradually increases until reaching the bow's peak weight (roughly 67# in this example) during the 10th inch of the powerstroke at marker (3). Then the draw weight begins to decrease (4) until finally reaching full let-off at marker (5) representing the end of the powerstroke (full draw). The spike in the middle of the graph represents forcibly overdrawing the bow (pulling against the wall). Some shooters tend to hold hard against the wall, others don't. So the spike in the middle could be different (taller/shorter) depending on the shooter.

GRIND IT BABY: Here's where it gets fun. The shape of that curve can be manipulated any way we like - depending on how we want the bow to feel and perform. The cam's general profile is sometimes called its "grind." Of course, cams are machined, not ground ... but anyway. The sample graph above is taken from a moderate bow with a relatively smooth-drawing cam (305 fps IBO Speed). Notice that the overall shape of the graph is a smooth bell-shaped curve with a gradual rise and gradual decline. Interestingly, the general shape of the curve is a good estimate of how aggressive the draw cycle will feel to the shooter. And as you might expect, some cams are specifically engineered to produce a smooth feel. Others are made for best possible performance. The actual geometry of the cam system determines how soft or aggressive the powerstroke will be. Take a look at the additional sample graphs below, taken from bows with different types of cam systems

multiple draw force curves for different cam designs

ROUND WHEEL: A Round Wheel style bow has a very smooth bell-shaped curve which rises to peak weight for only a moment then gradually descends to full let-off. This cam style will feel very smooth and easy to draw, but will store the least amount of energy and shoot the slowest. Although this type of cam has been around for decades, some shooters still prefer the soft feel of this style cam - particularly instinctive-shooters and finger-shooters. So there are a few traditional round wheels and cam grinds that replicate the round wheel powercurve still on the market, but slow IBO Speeds make them poor sellers. If you're interested in this kind of bow, don't expect much of a selection in the new bow market. Instead, consider buying a 20 year old wheel bow that's still in good condition - there are countless thousands on the used market - and they're cheap!

MEDIUM CAM: The Medium Cam graph is typical of today's basic single and softer hybrid cams with IBO speeds in the 300-320 fps range. These cams are more aggressive than wheels, ramping to peak weight more quickly and then coming to full let-off more abruptly. So they tend to store up more energy and shoot notably faster. However, a Medium Cam is still generally acceptable to most shooters. Most shooters will describe this type of cam as "smooth drawing," simply because peak weight doesn't persist throughout much of the cycle. For bowhunting and general purpose use, this type of cam offers a good blend of feel and performance.

HARD CAM: The last example is a Hard Cam system, optimized for maximum energy storage and speed. Notice how quickly the bow ramps up to peak weight and how quickly it transitions to let-off. Also notice the distinct high-plateau on the graph where the shooter must draw the bow over several inches at peak weight. This type of cam geometry will store dramatically more energy, and will usually have an IBO Speed of 330 fps or more. The downside is that Hard Cams feel harsh and heavy compared to other bows of equal peak weight. So they certainly aren't for everyone. But for shooters who want the hottest possible arrow speeds, the Hard Cam is the way to go.


overdrive binary camDRAW CYCLE OPTIMIZATIONS: Years ago we tested hundreds of bows on our draw-force machine and graphed their cam cycles. We were practically obsessed with it for a while. We discovered that some bow manufacturers clearly had their engineering down, the draw-force curves were clean and deliberate. Makers like Bowtech and Hoyt were controlling every moment of the drawstroke - nothing was incidental or haphazard. Other makers still had a few humps and ugly spots in their graphs - they hadn't quite gotten the geometry of their cams just right. But today, virtually every cam on the market has a drawstroke that is computer optimized millimeter by millimeter (which is no fun). Some cams are optimized for speed, some for comfort, and some try to find a blend between the two. There's no mystery left in cam geometry. The only mystery is in trying to predict what YOU want to buy. At what point will customers say a bow is "too aggressive" or "too harsh"? Where is that perfect blend where customers will think a bow has plenty of speed while still feeling that the drawstroke is smooth and comfortable?

graph of compound bow cams 1

HARD CAM VS. THEORETICAL MAXIMUM: If speed were the only goal, a draw force curve shaped like the graph on the right would yield the greatest possible amount of stored energy for any bow at 70# max draw weight and 30" draw length. Of course, a bow like this would be nearly impossible to aim and shoot. With a 0" brace height, the string would rest right on the bow's grip, and would nearly chop off your hand with every shot. And the bow would have no let-off, leaving you to hold back the entire 70# until release. A bow like this would be far more dangerous to the archer than it would be to the game animals. And although this graph is only a theoretical example, it can help us to understand how today's super-cam bows are yielding faster arrow speeds than ever before. But beware! The closer a bow's draw force curve comes to the theoretical limit graph, the more difficult it is to draw, shoot, and control.


THE BIG FOUR: Modern compound bows generally come with a choice of 4 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 that they all cam systems perform exactly the same. They certainly don't. But to say that one cam style really offers a crucial field-advantage over another would be something of a stretch today.

single cam bow SINGLE CAMS

Often described as a Solocam or One Cam, the Single Cam system features a round idler wheel on the top of the bow and an elliptical shaped power-cam on the bottom. The single cam is generally quieter and easier to maintain than traditional twin cam systems, since there is no need for cam synchronization. However, single cam systems generally do not offer straight and level nock travel (though the technical debate continues and every single cam manufacturer SWEARS their nock travel is perfect). Nonetheless, single cam bows still have a tendency to tune knock high, but that's certainly nothing newsworthy. It's par for the course.

Of course, all single cams aren't created equal. There are good ones and bad ones. Some are very fast and aggressive, others are quite smooth and silky. Some offer easy adjustability and convenient let-off choices, others don't. But most single cams do offer reasonable accuracy and a good solid stop at full draw. Overall, the smoothness and reliability of the single cam is well respected. The single cam is still a very popular choice on compound bows today.
hybrid cam bow HYBRID CAMS

The Hybrid Cam system features two asymmetrically elliptical cams: a control cam on the top, and a power cam on the bottom. The system is rigged with a single split-harness, a control cable, and a main string. Though originally invented and marketed by Darton Archery as the C/P/S Cam System, Hoyt's introduction of the Cam & 1/2 (a variation of the original C/P/S System) in 2003 brought hybrid systems into the limelight.

Hybrid Cams claim to offer the benefits of straight and level nock travel, like a properly-tuned twin-cam bow, but without the timing and synchronization issues. Indeed, hybrid cams require less maintenance than traditional twin cams, but it's probably a technical stretch to say that hybrid cams are maintenance free. They too need to be oriented (timed) properly for best overall efficiency and performance. There are several hybrid cam models available which are impressively fast and quiet, rivaling the best of the single cam bows.
binary cam bow BINARY CAMS

Introduced by Bowtech Archery as a new concept for 2005, the Binary Cam is a modified 3-groove twin-cam system that slaves the top and bottom cams to each other, rather than to the bow's limbs. Unlike single and hybrid systems, there was no split-harness on a binary system - just two "cam-to-cam" control cables. So the cams didn't pull on the opposing limbs - they pulled only on the opposing cams. This created a "free-floating" system which allowed the cams to automatically equalize any imbalances in the limb deflections or string and control cable lengths. So technically, this self-correcting cam system had no timing or synchronization issues and would achieve perfectly straight and level nock travel at all times.

Binary Cams have become a huge force in the industry. They're fast - really fast - and they're easy to tune. Ironically, the latest version of the Binary Cam, the "Overdrive Binary," moved the "free-floating" functions to an elliptical gear drive assembly inside the cam, and returned to the use of a split-buss cable to totally nullify the cam lean. So the most advanced version of the Binary Cam ironically looks like a complicated twin cam ... but it's not.
twin cam bow TWIN CAMS

A Twin Cam system is sometimes described as a Two Cam or a Dual Cam. The Twin Cam system features two perfectly symmetrical round wheels or elliptical cams on each end of the bow. When properly synchronized, Twin Cam systems offer excellent nock travel, accuracy, and overall speed. However, Twin Cams can require more maintenance and service to stay in top shooting condition. But thanks to today's crop of advanced no-creep string fibers, they are becoming increasingly easier to maintain.

Many hardcore competition shooters are quite loyal to the twin cam concept. And it's probably worth noting that the Twin Cam bow is dramatically more popular outside of the US and Canada, where there is less advertising to hype the single and hybrid systems. Aside from maintenance issues, the only true disadvantage to twin cams is the tendency for increased noise (compared to typical single and hybrid cams). Nonetheless, the Twin Cam is still the cam system of choice for many serious shooters. Twin Cams are also a very popular choice for youth bows since their geometry lends to large sweeping adjustment ranges.

CAM WARS: The cam wars are largely over. Ten years ago every manufacturer fought and clawed to promote their choice of cam technology. And while the bow companies duked it out, consumers somehow got lost in the nomenclature. Singles and twins were easy enough, but hybrids and slaved-twins, binaries, cams & a halves (there might even have been a cam & 2/3rds in there somewhere) just muddied the market beyond salvage. Fortunately, most buyers have gotten over their cam prejudices and all the cam technologies have matured. Today we're intelligently utilizing all the various styles throughout the market. Sometimes one cam style makes more sense - sometimes another. See? We can all get along.

CAM AGGRESSION: Today, the biggest obstacle with cams isn't the style of the cam, but rather the profile or grind of the cam (which often has nothing to do with the style or type). Some customers are still under the illusion that cams have magical powers of energy multiplication. We still struggle with the same customer objections year after year. Buyers want to go REALLY REALLY FAST but they also want smooth effortless drawstrokes with tons of valley and let-off. We will certainly offer the Unicorn Cam the moment it becomes available, but for now it's essential to understand - if a compound bow is faster, it's because it requires more total muscle energy to draw back. You have been so advised ...

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