Join Date: May 2006
Brace Heigth and forgiveness article
Copied from "Hunter's Friend"
Brace height is yet another important factor in the energy storage equation. A bow's brace height is simply the distance from the string to the pivot point of the bow's grip. You can kind-of think of brace height as how close the string will be to your wrist when the bow is at rest. The closer the string is to your wrist, the more work you have to do to get the bow drawn back. If you're drawing a 6" brace height bow back to a 30" AMO draw length, you'll have to pull the string back a total distance of 22.25" before you reach full draw*. But if the string rests farther back from your wrist to start, say the bow's brace height is 8", then you'll only have to pull the string back for 20.25". So the bow's brace height also figures into how LONG the bow's powerstroke will be. And as you know, a longer powerstroke generates more energy.
As a matter of energy storage, brace heights are analogous to the length of the rubber-band on a slingshot. If you hold a slingshot at arms-length and pull it back to your cheek, a shorter rubber-band would be stretched for a longer distance (and shoot faster) than the same slingshot with a longer rubber-band. In much the same way, a short brace height bow stores more energy and shoots faster than a tall brace height bow (all other things being equal). So brace height has the same affect on total powerstroke length as does the bow's draw length setting. The only difference is that the brace height determines where you start and the draw length determines where you stop. But unlike draw lengths, brace heights aren't adjustable. So you have to get this one right the first time. You can't change your bow's brace height later, should you change your mind.
If you compare brace heights and IBO speeds, you'll find an obvious correlation. Shorter brace heights tend to make for faster bows. Easy enough. Then it would seem that in order to get better performance from a compound bow, all you have to do is look for a model with a short brace height, right? Well, not so fast! Short brace height bows may be hot-performers, but they will come with a few drawbacks you should think about
*A bow's AMO draw length is measured 1.75" beyond the grip pivot point. So a bow's powerstroke distance is found by subtracting the brace height and 1.75" from the AMO draw length.
Brace Height - Speed vs. Forgiveness
If you’ve been shopping for a new compound bow, you’ve certainly noticed a variety of advertised brace heights, generally ranging from 5-9". But if shorter brace heights result in faster bows, then why aren’t all bows designed with short brace heights? Trade-offs! That's why. Short brace heights aren't automatically favored because a bow's brace height has a profound effect on the bow’s forgiveness and shootability. Short brace height bows are generally less forgiving and require more skill to shoot accurately. Since the arrow is in contact with the string for a longer distance and period, there is more opportunity for any glitches in your shooting form (hand-torque, trigger punching, etc.) to have a detrimental effect on the arrow’s flight. Longer brace heights have the opposite effect, limiting the effects of form glitches. In addition, very short (sub-6") brace height bows tend to yield more string-slap on the shooter's forearm (ouch!). So there are some trade-offs to consider here.
If you shoot with absolutely perfect form and technique, a short brace height bow will be just as accurate as it’s longer brace height cousins. But if you have average skills and are prone to occasional goof-ups, a bow with a little longer brace height will yield better accuracy in most shooting situations. The average new compound bow has a brace height of approximately 7". Bows with shorter brace heights (5-6.5") will be faster but less forgiving to shoot. Bows with longer brace heights (7.5-9") will generally shoot slower but will be more forgiving to your errors. Consider this carefully when choosing your new hunting or 3D bow. Unless you have a specific need for a blazing fast bow, you may find that a more moderate brace height will increase your enjoyment of archery and your success in the field. SPECIAL NOTE: Tall guys with draw lengths 30" and above should be especially conscious of brace height - as a long draw length and a short brace height are a particularly bad combination, especially for new shooters.
Brace Height Market Trends
Just as 300 fps seems to be the accepted IBO speed-minimum, 7 inches is the generally accepted brace height minimum in today's compound bow market. If you visit our compound bow specification charts, you'll surely notice that a disproportionate number of bows are advertised with exactly a 7" brace height. This isn't by accident. Experienced shooters - particularly bowhunters - tend to avoid short brace height bows, regarding any brace height under 7 inches as "radical" or "unforgiving". So a bow with a 6 7/8" brace height is often a lame duck - at least regarding bow sales. As such, most manufacturers try to aim to hit the market-pleasing 7+ inch brace heights on most of their new bow designs. As a matter of selecting a new bow, we submit there's probably no justification for such an exacting prejudice, as there's nothing particularly lucky about a 7" brace height. But that does seem to be the commonly accepted line-in-the-sand between performance and shootability.
Short-Draw Archers - Built in Forgiveness
If you are a short-draw archer (27" draw length or less), you'll be pleased to know you have a nice advantage regarding forgiveness and shootability on your compound bow. As we noted earlier, a bow which has a 6" brace height and is set for long 30" draw length will have 22.25" powerstroke. This means the during the shot, the arrow will remain in-contact with the string for approximately 23-24" (including string follow-thru) until the arrow finally releases. This would generally make for a rather unforgiving setup. But that same bow in the hands of the short-draw archer will be considerably MORE forgiving to shoot. If a short-draw archer shoots the same bow at - say - 26" draw length, his/her powerstroke will only be 18.25" long. So the short-draw archer's arrow gets off the string in a shorter distance - thus the short-draw archer has some "built-in" benefits of forgiveness. If you are a short-draw archer, don't spend too much time fretting over brace height. Instead, consider shooting a bow that's a little more aggressive. The same bow that might give your 6'4" hunting buddy fits, will be quite manageable when set for your short draw length. And choosing a more aggressive bow will help you to recover some of the speed and power lost in a short-draw setup.
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