« previous next »
Pages: [1]

Author Topic: Formula for increase in draw weight  (Read 2735 times)

0 Members and 1 Guest are viewing this topic.

Offline WillS

  • Member
  • Posts: 1,905
Formula for increase in draw weight
« on: April 17, 2013, 04:16:01 pm »
Quickie question for anybody who knows - if you know the draw weight of a bow at a certain draw length, is there a formula / calculation to work out what the weight will be at a different given length?  For example, if a bow is say 50# at 18", is it possible to work out what the draw weight will be at 20", 22" and so on?
Logged

Offline PEARL DRUMS

  • Member
  • Posts: 14,079
  • }}}--CK-->
Re: Formula for increase in draw weight
« Reply #1 on: April 17, 2013, 04:17:52 pm »
I use 2.5# per inch and it will get you withing a few pounds.
Logged
Only when the last tree has died and the last river has been poisoned and the last fish has been caught will we realize we cannot eat money.

Offline WillS

  • Member
  • Posts: 1,905
Re: Formula for increase in draw weight
« Reply #2 on: April 17, 2013, 04:20:23 pm »
Cheers Pearl.
Logged

Offline PEARL DRUMS

  • Member
  • Posts: 14,079
  • }}}--CK-->
Re: Formula for increase in draw weight
« Reply #3 on: April 17, 2013, 04:33:53 pm »
Will if you scale your bow at 18" and it reads 42#, you can basically expect it to remain close to 2.33# per inch as you pull farther until stacking occurs past 90 degree's.
Logged
Only when the last tree has died and the last river has been poisoned and the last fish has been caught will we realize we cannot eat money.

Offline adb

  • Member
  • Posts: 5,339
Re: Formula for increase in draw weight
« Reply #4 on: April 17, 2013, 04:39:11 pm »
I find my bows are more 3-5# per inch. Some of my warbows above 90# have been as high as 7# per inch.
Logged

Offline WillS

  • Member
  • Posts: 1,905
Re: Formula for increase in draw weight
« Reply #5 on: April 17, 2013, 04:52:22 pm »
How much does the brace height affect this?  I'm asking as I'm currently tillering a yew longbow, and it's at a low (2 inch) brace height so basically just a v. tight long string at this stage and it's dead on 50#@18".  Does the formula still remain the same, or does a higher brace height change things?  If we average out Pearl and Adb's answers and say about 3#/inch, does that mean that at 28" I should be expecting 80#, or will that go up/down once I'm at full brace?

Normally I don't consider this stuff, I just tiller out to my goal draw weight and so on, but it's too dark outside to use the tiller so I'm in "think" mode instead!
Logged

Offline PEARL DRUMS

  • Member
  • Posts: 14,079
  • }}}--CK-->
Re: Formula for increase in draw weight
« Reply #6 on: April 17, 2013, 04:57:27 pm »
Your math sounds right to me Will. Brace height doesnt affect draw weight.
Logged
Only when the last tree has died and the last river has been poisoned and the last fish has been caught will we realize we cannot eat money.

Offline adb

  • Member
  • Posts: 5,339
Re: Formula for increase in draw weight
« Reply #7 on: April 17, 2013, 05:44:19 pm »
I don't know for sure, cuz I've only ever measured this at full brace. I wouldn't think it would change much, if at all.
Logged

Offline PEARL DRUMS

  • Member
  • Posts: 14,079
  • }}}--CK-->
Re: Formula for increase in draw weight
« Reply #8 on: April 17, 2013, 05:48:38 pm »
The limbs have to bend the same distance whether it starts at a 3" brace or a 6" brace, therefore the draw weight doesnt increase with a higher brace. The string will be tighter at a full brace, but the end draw weight will remain.
Logged
Only when the last tree has died and the last river has been poisoned and the last fish has been caught will we realize we cannot eat money.

Offline WillS

  • Member
  • Posts: 1,905
Re: Formula for increase in draw weight
« Reply #9 on: April 17, 2013, 05:54:58 pm »
Great, cheers for the replies guys!
Logged
Pages: [1]
« previous next »