I'm no expert, but I think if you need to reduce weight significantly, you'll lose more weight by trapping the belly. I spoke with Steve Turay (Northern Mist Longbows) a couple of years about this. According to Steve, the fiberglass provides more stiffness (resistance to bending of the limbs; draw weight) in compression (belly) than in tension (back). So Steve traps the back on his longbows because his thinking is that if he narrows (traps) the back by a given amount, the bow will retain more draw weight than if he were to narrow (trap) the belly by the exact same amount instead. So, either way he would be removing the same amount of material (mass, weight) from the limbs, but by trapping the back the bow will end up with a higher draw weight than if he trapped the belly. Lighter limbs for a given draw weight is his preference-- squeezes a little extra performance out of the bow. So, his experience has been that he'll lose less draw weight by trapping the back instead of the belly.
Macbow says above "It has been written somewhere that removing the width on the back adjusting tension strength is prefered over reducing the compression on the belly side." This may be for the same reason that Steve does his bows this way-- to maximize performance, not to maximize the reduction in draw weight.
But I'm guessing the difference in performance isn't all that much. It sounds like you need to get a significant draw weight reduction, so I think you'll get more weight reduction by trapping the belly than the back. Or as Roy says above, you could narrow the limbs. If you really need to drop weight, you could narrow the limbs and also trap the belly (depending on the current limb width).
Topic: which side to trap? (Read 720 times)
