Poundage Efficiency of Modern Recurves

[Orion]

Kirkill, you're not really disagreeing, just elaborating.  However, the issue you raise seems to have already been addressed by bow makers.  Bow makers, including the big manufacturers of the 40s, 50s and 60s, have always made their lighter bows with thinner glass and wood laminations, i.e., keeping the core to glass ratios roughly the same.  If they made them with the same thickness glass and wood stack, the only way to make them lighter would be to thin the limbs side to side -- a lot -- or make them a lot longer.  Then it becomes a different bow.  In short, lower poundage bows can't be built exactly like higher poundage bows.

[**DONOTDELETE**]

Lyonel
I think if i had to pick a particular weight bow to build in a speed contest at 10 gpp arrow weight it would be right in there around 51-52 pounds. that seems to be the point of diminishing returns building hot rods.

there is a ton of really interesting stuff in this bow building. it's all a balancing act with trade offs.

Orion,
This isn't the first time I've been accused of trying to re-educate the masses. but actually this isn't my intent at all. There are a lot of folks out there that shoot these bows that are just down right curious why one bow performs so much better than the next one.

Most bowyer's are a secretive lot as far as discussing limb design goes, and it's quite understandable too. it takes a long time to get as nice shooting design dialed in.

I don't know where the break off points are on changing glass thickness from .030 to .040 and .050 glass on production bows. but there are lines drawn somewhere and all these bows do not perform the same. These guys can't take time to grind glass and use different mass weight core materials  from one weight bow to the next to insure higher performance like a custom bowyer can..... but... they are sold at a lower price.

where I've really notice the difference is in bows being shot at shorter draw lengths that are designed for longer draw lengths.  i don't know very many bowyer's that alter the length of the working limb in the cores to accommodate different draw lengths, much less actually grind their glass to keep core to glass ratios the same.
most bowyer's don't even grind their glass at all.
They use .040 glass on everything from 40 to 60 pounds and call it good.

the bottom line is lower poundage bows built exactly the same as higher poundage bows will not perform the same without alterations in the core and shifting wedges. even then.... it's a tough one to pull off at sh0rter draw lengths. IMO

They say it's all been done before, and maybe they are right. but i sure enjoy seeing a guy that has a short draw length enjoy a higher performance bow than he can get from a production model designed to draw 32". You get what you pay for sometimes.

John,

Testing of lighter weight bows at 28" draw, 9-10 gpp using .040 glass with a shooting machine. i'd have to say the diminishing returns start once you drop below 45 pounds. it really becomes noticeable at shorter draw lengths. The pre-load of the lower poundage bow needs to be increased to keep the performance up there. I've found it's most noticeable on high speed video.  of course different limb designs, and recurve's, vs long bows, vs hybrid long bows, all vary in test results.

All this stuff may have been done before, but i certainly haven't done it all. i just find it incredibly interesting how much the little things you do to these limbs make such big differences.

Kirk

Not disagreeing with anyone, just a question. I had BW target bows that shot everything from light target arrows to Bear 308s with 125 grain points, my 42pounder was  faster than shorter hunting weight recurves with those 308s.  I spent a little time with a kid that was heading for the Olympic trials that had a number of different bows, mostly Yamahas, what surprised me was how much testing he was doing looking for a good arrow to shoot in a cross wind, he ended up with  ten grains per pound, when he fired it through his chrono they were fast. I do not remember the exact speed, but I was fairly shocked what he got out of a 40 pound bow. His bows ranged from 64" to 68", there has to be more than just length that gave those light weight bows that kind of power. When Kirkill states that he had trouble designing a light bow to perform with a heavy bow, that is different than what my old PAA pro friend always said, "you will never find a 58" hunting bow that will perform like a top of the line target bow, that is why I hunt with a 40 pound target bow." He proved it by shooting my arrows and they were obviously every bit as fast as my Bear Kodiak shot them and more accurate.

[Sixby]

I'm feeling so smart by staying out of this.  

So no diminishing returns\\? No place where poundage with 10 gpp arrow starts losing speed? You are saying that a bow that is 55 lbs shooting a 550 gr arrow 190 fps will with same exact design in a 70 lb bow shoot a 700 gr, arrow 190 fps. That there is no place where there is an optimum weight that uses the energy of the bow the best? Not saying here what I think but these are honest questions and I wold appreciate input.

God bless you all and Merry Christmas.

[Glunt]

I think there is an optimum weight, but it is different for every design and every bowyers approach to what they change when going from 30# to 70#.

That is my official unscientific and baseless opinion.  

[**DONOTDELETE**]

my old PAA pro friend always said, "you will never find a 58" hunting bow that will perform like a top of the line target bow  

i could give you a list of a dozen different bowyer's that would make a $1000 bet against that statement if this pro was just talking speed, and i'm one of them....    

but..... over all performance is measured in different ways by different sorts of archers using their bows for different purposes.

[oldtimerbow]

I had this discussion with a good bowyer freind who shoots heavy weight bows.He said there is a point in weight where you are not gainig anything in speed but you gain the ability to shoot a heavier weight arrow with more efficiencey.