Larry Wise - "Tuning your
compound bow"
If you anchor on the front slope (before you get into the valley) shots will go erratically high - reason being they start off at a faster acceleration.
If you anchor on the back wall / stops, you get a ripple start to the arrow's flight. It gets an initial kick, then slows down before it speeds up again, a bit like "kangaroo petrol" on a car. It's not a smooth getaway... and shots tend to go erratically high and mayb even low for no apparent reason.
If you're in the middle of the valley, you get the "gentle" acceleration to peak weight.
Ah Larry Wise, how you wasted years of my life.
I use to use this book religiously back in the late 80's early 90;s to tune my bows. Then after years of frustration I threw it out and worked it out myself and got results. It's criminal that it is still sold and worse yet used by people.
This quote is seriously incorrect and does not match up at all with how the actual physics of
compound bows work.
The key points here is that he has assumed that the the bow loses energy for a second if shot from the back wall, this is grossly incorrect. The energy is stored and on release the cables now do very little, the acceleration and energy transfer is relatively constant. (it does increase in acceleration but does not increase, then decrease and then increase as he is saying)
Now here is the key to his confussion
"and shots tend to go erratically high and maybe even low for no apparent reason."
OK if his concept was correct it would be one or the other. So why the randomness?
The reason is nock travel.
Remember when this book was written there was only twin wheel or twin cam systems out there. Timing was critical and cam design primitive. If your timing was wrong then you had very sensitive nock travel. Sometimes no matter how good your timing was you had nock travel problems anyway. Thus the bows were only accurate from the middle of the valley. This is also where Tiller tuning came from. Tiller tuning is not the balancing of your limbs, it is micro adjustment of your nocking point location and nock travel. For example I can move the angle of nock travel on a
Hoyt Trykon by 1/2" by taking one turn off the top limb.
So the reason why tiller tuning improves groups for some is that they have now micro adjusted their cam timing to reduce the effects of poor nock travel. That's why it is a waste of time on most modern bows.
Now walls.
If your bow has a distinct middle of valley and a wall as described by Wise then please go buy a bow made in the last 10 years.
The wall as we know it today is actually a movable draw stop that is designed to sit within the valley and move forward and back of the valley to adjust draw length. If you set the draw stop in the cam's middle position your are shooting from the middle of the valley when pulling against the wall.
With a well designed modern bow you can shoot from the front or the back of the valley and get the same results.
Using a Hooter shooter I tested a guardian indoors. Hitting the same hole I then drew 3" short of the valley and fired. Same hole. I then drew about 60lb past full draw. Same hole.
Reason is that the bow's nock travel is very flat in those areas.