I got the following question from one of my students. It is about compound bow set up.
“What is Coach Larry Wise talking about when he suggests “adjusting your draw length to shoot from the middle of the valley?” Is he saying you don’t want to be against the wall? Many of the new 2017 bows make big points about being able to adjust the hardness of the wall so why would you want not to be against the wall? Is there a way to adjust the draw length via twisting the string to put you in the middle of the valley? Doesn’t that also decrease the let-off?”
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Here is my response:
Some Background for Coaches Not Compound Fluent Yet
The valley is jargon for the segment of the force-draw curve of a compound bow (see illustration) right at full draw. The force exerted by the bow drops steadily from peak weight until a minimum is hit at the “bottom of the valley” and then it skyrockets thereafter. Because the draw force increases so quickly after the valley is reached, it feels like one is pulling against an unmovable object like a wall, hence the jargon “the wall” for that segment of the FD curve (again, see the illustration).
Shooting from the “middle of the valley” was common advice back in the day of round wheel bows (aka “wheelies”). My mid-1990’s PSE Magnaflite bow had a 2˝ wide valley as an example. With the advent of high performance, dual-cam “speed bows” and one-cam bows, the valleys were so short that you had to be in the middle of the valley, whether you wanted to or not. With more moderate cams such as are on today’s bows, the middle of the valley is still the place to shoot from. You do not want to “pull hard against the stops” (PHATS). The PHATS strategy was invented, I believe, on the fly by an archer who was creeping at full draw as a way to prevent creeping. But Tom Dorigatti has shown in one of his more brilliant Archery Focus magazine articles that doing that (PHATS) results in draw lengths that vary by as much as a quarter of an inch creating more vertical dispersion in your arrow groups.
Larry’s argument, one that I subscribe to (it is hard not to agree with Larry), is that a key to performing well is being relaxed. PHATS disrupts any such relaxation you might muster and doesn’t provide anything of value. Larry teaches that you have to set your bow’s draw length so that you hit perfect full draw position when you are in the middle of the valley, and that you hold that position because it is your full draw position (draw elbow straight back behind arrow), not because the bow is preventing you from pulling farther. This allows you to relax and even though there is variation in all positions of your body from shot to shot, the minor variations in a comfortable feeling elbow position (at which point your elbow is on an arc pointing sideways to your arrow, so not affecting the draw length all that much) results in only small changes in draw length, which because you are near the center of the valley, result in the initial launch conditions of each arrow being virtually identical. (The FD curve is basically flat at the bottom of the valley, so if you move forward or back ever so slightly from the middle, the draw force soon to be acting on the arrow is essentially the same (again, see the illustration).
Regarding “Is there a way to adjust the draw length via twisting the string to put you in the middle of the valley? Doesn’t that also decrease the let-off?” Most bows only allow adjustments in draw length via modules, etc. in one half inch or one quarter inch increments (1/4˝-1/2˝). Pros won’t accept more than 1/16˝ error in their own draw length, so yes, you will have to twist strings and or cables to accomplish these. There are too many schemes to be able to state a generic process for doing so, but in general twisting cables makes for larger changes than twisting bow strings. And, yes, this does affect let-off but so do draw weight changes. The listed let-off of bows is determined at one particular draw length and weight and varies slightly when either of those variables is changed (see image as example).
The changes due to cable or string twisting/untwisting are so small as to change the let-off only a very small amount, so not to worry.
As to why manufacturers are offering “features” to adjust the feel of the Wall one is pulling against, I guess we shouldn’t criticize them from giving us what we are asking for. We should OTOH be more careful in what we are asking for.
Does this make any sense?