| Spine in short has little to do with the lbs of the bow, but the force of which the arrow is being pushed.
If the same arrow is being pushed to a speed of 180fps on one bow and 210fps on the other bow then there is going to be a difference in the force being applied to the arrow. It is still being pushed over the same distance say 20" of power stroke, and the arrow has the same mass to be forced into changing speed.
The Idea that all limbs need an approximate spine for the draw weight is the easiest way of measureing it. The fun begins when you consider that the more spine needed the more material needed in the arrow the heaver the arrow gets. that is why faster, heaver bows dont shoot hugely faster then light fast bows. The idea that more weight in the back and of the arrow/string/limbs the slower the bow goes, the less spine needed. Simply due to it being harder to accelerate the mass of limb/string/arrow. If you load up the front of the arrow, you start to have a different effect, in that the back of the arrow wants to accelerate, but the front weights a ton, so it wont move, effectivly weakening your dynamic arrow spine.
The next issue to consider when adding back weights and pile weights is you cant just go crazy. The balance point (FOC, Forward Of Centre) of the arrow needs to be up near the pile end, for example, when you watch someone throw the hammer in the field events you can see that the heavy end will overtake the light end. If the back of your arrow is heavier or two equal to the front then instability will take place in flight, thats why there are so many different spines of arrow.
You have just stumbled into the difference between static spine and dynamic spine.
Does that help or have i just jumped off the deep end.  |