Limbs Trying to work out recurve limb weight for a child!

nbuuifx

Member
I'm getting to the point where I think it is just guess work!

I'm in the situation where I don't want to buy new limbs and the nearest archery store is that bit too far away to make it worth while going and trying kit out.

Basically my daughter currently shoots recurve. She has a Hoyt Excel 21" Riser and some 14# limbs. The tiller bolts are currently wound in all the way and it gives 11# at the fingers. I think draw length is only around 20" - will check next time her bow is strung up.

She is finding 11# OTF far too easy and can hold it on full draw for an age. It has been useful for her to work on her form but I think it is time for her to increase. I would like to try and get some that would be around 15# OTF for now.

I've actually ordered some that seemed a good buy, with the thought that if they are too heavy I can save them for a year or two, or just sell them on.

The ones I've bought are 22# limbs. To be honest I'm guessing they will be too high at 8# heavier but I can wind the tiller bolts out the full 6 turns.

I just have no idea what it will end up on! I have a hoyt horizon as my riser. I know that my limbs give 38# OTF, with the tiller roughly in the middle. The range on mine goes from 36# all the way out to approx 40# all the way in. So I have a 4# range. Will this be similar on my daughters? Or is the range a percentage or the actual draw weight?


If I start with hers being 14# limbs (measure at 66") - these become 18# limbs at 62", but then if I take 2# off for each inch less than 28". Then I end up with them being 2# limbs! So obviously that doesn't work out!

With the new ones being 22#, this would become 26# at 62", but then take of 16# again - makes it 10# at a 20" draw.


Or looking at it the other way if the current ones are 11# and we do get a range of 4#, then they could be 7# wound all the way out.

If the new ones are literally just 8# more then this would give 15# to 19#.


Wow - I feel even more confused! I guess the problem is that junior stuff really takes the calculations to the extreme limits which nobody normally worries about. I presume the guesstimate rules become further and further out the further you deviate from the norm.

This is partly the reason that I thought, what the hell, and ordered the 22# ones. At least then I can make a comparison and given the good price, I can easily sell them on if required.

It seems to me that with kids growing and changing draw length on a regular basis (which will then quickly put the poundage up), that ideally I could do with a selection of all the different weight limbs to keep changing between to keep the poundage at the right sort of level!

What do you reckon?! Make your guesses! What do you reckon 22# limbs will be OTF at a 20" draw on a 62" bow, with the tiller bolts wound out 6 turns!?
 

Rik

Supporter
Supporter
The weight adjustment isn't quite as simple as that. A better rule of thumb than "2lbs per inch" is "5% of the measured draw weight per inch" but even that is only a guesstimate. If I do that with the 14lb limbs, I get 10.8. Close enough.
The same calculation would make the 22# limbs come to about 16#. But you'd need to add an error bar to that. Probably not as much as +-1#.
 

nbuuifx

Member
The weight adjustment isn't quite as simple as that. A better rule of thumb than "2lbs per inch" is "5% of the measured draw weight per inch" but even that is only a guesstimate. If I do that with the 14lb limbs, I get 10.8. Close enough.
The same calculation would make the 22# limbs come to about 16#. But you'd need to add an error bar to that. Probably not as much as +-1#.
Thanks for that 16# doesn't sound too bad. Is that taking into account winding the tile bolts out? Or is that with everything left the same?
 

AndyS

Supporter
Supporter
If you're replacing like for like except for the poundage, i.e. same riser, same length limbs, same draw length, then rather than trying to estimate the # per inch, I would have thought that a simple percentage calculation would give a reasonable idea.
Whatever your daughters draw length is, she's getting approx 79% of the limb rating @28", so assuming that a heavier limb will have a very similar DFC shape, just a steeper one, then 79% of 22# could be around 17.4# at her current draw length with the limb bolts fully in. Hoyt's manual says "Hoyt Recurve bows are adjustable over a range of approximately 10%" so in very rough terms, winding the bolts fully out might then drop that to around 15.8# - which is pretty similar to Rik's estimate just using a slightly different approach.
 

AndyS

Supporter
Supporter
Having re-read Rik's post, maybe my answer doesn't quite match Rik's, because I suspect from the "The same calculation would make" comment, that his 16# estimate is for the bolts fully in, because that's where your 11# figure comes from.
 

nbuuifx

Member
Interesting, thanks Andy. The 10% with filler fits in roughly with my findings on my bow.

The only variable is the make of limbs is different and the construction. The original ones are a bamboo core, the replacement will be a fibre foam type (I think! - replacement are mybo synergy air)
 

Rik

Supporter
Supporter
This is where the minefield gets a bit trickier... :)
My back of a fag packet calculation is really intended to work from measured weights, so if you can confirm a weight at a particular draw length and tiller settings, you can get a reasonable estimate of the weight at another draw length (assuming a more or less linear draw/force curve).

But when you compare different makes of limbs, you can't assume that they will weigh the same at the same tiller, even if they have the same marked weight (and that marked weight is accurate, which it sometimes isn't). Plus, the allowed error on the marked weight (+- 1#) can be proportionally more significant on lighter limbs.

If the original limbs were Hoyt, and the new ones are Mybo, then at similar tiller settings and same marked weight I would expect the Mybo limbs to weigh heavier than the Hoyt. Not by much, but when you take the maximum possible error into account, they could be up to 3 pounds heavier than you might expect. And still be considered to be marked correctly.
 

Hawkmoon

Member
Just a quick thing, if you think of each additional 2lbs weight on the fingers as an extra bag of sugar, it can give an idea of the effect it will have on the archer. Lots of adult archers think that adding six or eight pounds will be an easy transition, but if you imagine that you are already holding fifteen to twenty bags (of in your daughters case about five, they are actually 2kg with is 2.2 lbs), it can take quite a while to get used to it. If there is a shop you can use (even mail order) who will do a limb exchange scheme that would be a great way to bring up her limb weight slowly so as not to loose her form.
 

nbuuifx

Member
Well they arrived and as suspected they are a bit too heavy for her.

I re checked her current limbs with her current draw length and they were actually 12lbs with the limb bolts wound all the way in. She is finding this far too easy.

I put the new limbs on and checked the OTF weight, it came out as 18.6lbs. I wound the limbs out 6 turns each and checked again hoping for a good drop but it only dropped it to 17.6lbs.

I think a 5.6lbs increase is too much, especially given it is nearly 50% of the original weight.

On the bright side it does give me another point of reference. What I now know:


Kinetic Bamboom Limbs marked at 14# (66") come out as 11# to 12# at her current draw length on her 62" bow. (-2# to -3# compared to what is marked)

Mybo Synergy Air Limbs marked at 22# (66") come out as 17.6 to 18.6# at her current draw length on her 62" bow. (-3.4# to -4.4# compared to what is marked)

So hopefully a set of 18# limbs (which is what I was really after) will come in at somewhere between 14# and 16#. Will keep on the hunt!
 

Whitehart

Well-known member
When the limb bolts on the Excel 21" are wound out 6 turns do the limbs fit correctly on the limb bolts. I have found in reality, in the past no more than 5 turns is max to have the limbs working correctly partly down to the extreme angle and the shape of the detent slot.
 

nbuuifx

Member
The limbs were very difficult to remove when wound out 6 turns, to make it easier I turned them in until I was able to easily remove.

I remember when testing my bow the final turn in and the final turn out were negligible, most of the difference was around the middle.
 

srfairclough

New member
I have experienced the same. Both of my children; 8 year old son and 12 year old daughter shoot 21? risers. My son has 18# limbs fully in, and my daughter has 20# limbs out to five turns. I believe that lower poundage limbs don?t scale with draw length the same as higher poundage limbs on 25? risers do. My son finds his limbs relatively easy whilst my daughter is content with hers. Both limbs are SF axioms.


Sent from my iPhone using Tapatalk
 

nbuuifx

Member
I have experienced the same. Both of my children; 8 year old son and 12 year old daughter shoot 21” risers. My son has 18# limbs fully in, and my daughter has 20# limbs out to five turns. I believe that lower poundage limbs don’t scale with draw length the same as higher poundage limbs on 25” risers do. My son finds his limbs relatively easy whilst my daughter is content with hers. Both limbs are SF axioms.


Sent from my iPhone using Tapatalk
Well if you get to the point of selling the 18# limbs (assuming they are short) - then drop me a message as I'd be interested to give them a go!
 

munchkin

Supporter
Supporter
Hah! I have had this problem my whole archery career, with a draw length of about 22in. I have just just checked my limb collection, and do have a set of 18lb ones but they're medium, so probably no good for your daughter.
 

nbuuifx

Member
Just as an update, we ended up getting a set of 20# limbs which worked in nicely. They were only 2# less but it made all the difference!


Previously I had found...

Kinetic Bamboom Limbs marked at 14# (66") come out as 11# to 12# at her current draw length on her 62" bow. (-2# to -3# compared to what is marked)

Mybo Synergy Air Limbs marked at 22# (66") come out as 17.6 to 18.6# at her current draw length on her 62" bow. (-3.4# to -4.4# compared to what is marked)





I ended up with Kinetic Kosmo Limbs 20# (66") which at 5 turns out have come out at 15# OTF. Wound all the way in they become 17.5# which gives a nice cross over point to the mybo Synergy limbs.

She's shot them for the last couple of months and seems great with them, I plan to slowly tweak the tiller bolts in to increase the poundage very gradually.
 
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