What bow are ya shooting and I can get ya darn close. If it is a high performance recurve than add 15#s to the bow weight and 5#s more for every inch over 28"s. I would say ya need 75-80#s spine. If ya cut them to 28"s than 70-75# would work. I shot just about every bow out there and my modern recurves(Blacktail,Widow,Brack,RER etc.)that were 60-63#s used this formula. My last heavier bow a Kwyk styk was 63#s at 28"s and I shot a 29.5" cedar with a 125 grain point spined 80-85#s. Go to arrowsbykelly.com and check out the spine charts they are on the money. Shawn