Riddle me this Batman.. a question about draw weight

[Bradford]

So I pulled my new bow to about 28" and got 65# out of her.

Here is the catch.. I am using a 61" string on a 62" bow.. just for break in and check alignment.

Will the weight change at all with a 59" string?  My math says no, but there is two less inches of string to help pull it?

[rmorris]

My vote is it will increase the weight of the bow with a shorter string. Here is my reasoning... once you put a shorter string on the bow you are pre-stressing the limbs therefore adding more weight to the bow... example #2 if you had a 62" string on a 62" bow the force on the string should be 0# if you put a 1" string( yes I know this is impossible) on a 62" bow imagine the force on the string. Therefore the shorter string you put the more you pre-stress the limbs. Please let us know the results... you have riddled me.

[Bradford]

I see your point.  My train of thought was the leverage factor...a bigger stick prys up the rock easier..
We shall see.

[Crooked Stic]

Longer string just lowers you brace hieght. final weight will not change. Just have a higher starting point with the right string.

[psychmonky]

Not arguing, just adding food for thought, but wouldn't a shorter string stress the limbs differently than a longer one? it would seem like a longer string would pull the tips straight toward the floor (on a tree) and the shorter string would pull the tips more toward the center...

[Roy from Pa]

Shorter string just pulls the bow a couple more inches from the brace height of a longer string, just like you do when you start to pull the bow. The final weight at your draw length will not change. However a longer string/lower brace height will keep the arrow on the string a little longer when shot, resulting in force being applied to the arrow longer.

[DVSHUNTER]

Crooked and Roy nailed it, only the length of the draw changes. Pulling a bow from three inches to twenty eight is not any different than pulling it from seven inches to twenty eight, just a shorter power stroke so to speak. Good question though. Knowledge is power!

[bjansen]

I still think it is going to increase a bit...not much, but I think it will increase given the additional pre-load on the limbs with a shorter string.  Lets hear the results when you get them.

[jsweka]

OK, I had to get some empirical data on this.

I've got a 62" mild r/d bow and I just tried different string lengths to see the effect on draw weight.  Here's the results

1.  58" string = 8 7/16" brace heigth = 60.5# @ 28"
2.  59" string = 7 7/8" brace heigth = 60.5# @ 28"
3.  61" srring = 5 1/2" brace heigth = 59.5# @ 28"

So I would say string length/brace heigth will have negligible effect on draw weight within the ranges we would likely use on a given bow.  I certainly wouldn't shoot with the 61" string on a 62" bow.

[John Scifres]

My experience is that it will increase.  It has a lot to do with string angle though so limb shape has something to do with it.  That is in line with your leverage intuition.  Going from almost zero brace height to 6+" will make a difference.  Try it.  Report the results.

[Bradford]

Thanks everyone.  The bow is almost done, so the new string will be on it soon.  I was getting 65# at 25 in, so i did a little sanding to get it 64# at 29 in.  That is why i was asking... i dont want it to be to heavy.

[Pat B]

Once I get a bow to brace height I go with the appropriate string length. Like John said the string angle is different depending on the string length. Early on in the building process I use a long string until I get the tips to move 6" to 8" then go with a shorter string. If you use a longer string the leverage is different(a long string pulls the tips down and a shorter one pulls it more inward) and this casn make a difference in draw weight.

[Bradford]

I think I will be all right.. I just twisted the 61" string to about 60".. and I measured 65# @ 28".  So one more inch in theory should make it 66#.. but I still need to finish sand the limbs which will help lower it a pound or two.. I will so a little extra "rounding" on the edges to help it come in at weight.

My local shop was out of 59".. pain in the butt.

[Pat B]

Generally rounding edges has little effect on bow draw weight(at least in wood bows). Those corners do very little work and are basically dead weigh. By removing them you are reducing the physical weight without affecting the draw weight so theoretically you could be increasing the limb recovery speed without decreasing draw weight.