For Agument's Sake

Joined
Feb 25, 2012
Messages
2,830
Location
Michigan
Let's say you have two bows (same model) where one is 70# and one is 80#. The bows miraculously shoot bullet holes with the same hunting arrow. What is the difference in draw lengths (obviously the 70#er would be longer stroked) to get the same speed?
 
For most bows I'd say 2".

So a guy shooting a 30" draw at 70lbs would be fairly equivalent to a 28" draw guy shooting the same bow at 80lbs.
 
I shoot and hunt with a compound. The draw length on a compound does not determine your poundage , the limbs on the compound determine the poundage. The draw length you choose is specific to each person and is based on your physical size. So you can still have 80 lbs of pull on your bow if you have little arms and a small draw length.

Now draw length and poundage both affect arrow speed. I do not shoot traditional and I think I know the answer but ill let someone else chime in that knows the answer for sure .
 
I shoot and hunt with a compound. The draw length on a compound does not determine your poundage , the limbs on the compound determine the poundage. The draw length you choose is specific to each person and is based on your physical size. So you can still have 80 lbs of pull on your bow if you have little arms and a small draw length.

Now draw length and poundage both affect arrow speed. I do not shoot traditional and I think I know the answer but ill let someone else chime in that knows the answer for sure .

Lol he knows draw length doesn't affect poundage.

He's asking how many extra inches of draw gain the same amount of speed as 10 pounds of weight.
 
If memory serves, you get about 1.25 fps/# increase in draw weight (12.5 fps/10#). You get about 10 fps per " of DL. Based on that, it would be closer to 1.25" in additional DL than 2" to get a 70# bow to shoot the same speed as an 80# bow.
 
If memory serves, you get about 1.25 fps/# increase in draw weight (12.5 fps/10#). You get about 10 fps per " of DL. Based on that, it would be closer to 1.25" in additional DL than 2" to get a 70# bow to shoot the same speed as an 80# bow.

My bows are right at 20fps difference for 10lbs draw difference. That's the same bow turned down to 60 or all the way up to 70.
 
I agree.

The general rule of thumb is:

10 FPS per inch of draw length
1.5 to 2 fps per pound of draw weight - this can depend on let-off
 
My bows are right at 20fps difference for 10lbs draw difference. That's the same bow turned down to 60 or all the way up to 70.

It used to be (in the pre-parallel limb days) you would lose both poundage and draw stroke by backing out the limb bolts, so you were in essence changing 2 different variables at the same time. Part of the speed decrease was related to poundage and part to the change in brace height/stroke. I cannot say whether the same is true with the geometry of today's bows, but a better comparison might be to compare 60# and 70# peak weight bows (all else equal).

That begs the question of whether a 70# bow backed off to 60# would generate the same speed as a 60# bow maxed out (all else equaly)? I would doubt it, but have no data to support that either.
 
It used to be (in the pre-parallel limb days) you would lose both poundage and draw stroke by backing out the limb bolts, so you were in essence changing 2 different variables at the same time. Part of the speed decrease was related to poundage and part to the change in brace height/stroke. I cannot say whether the same is true with the geometry of today's bows, but a better comparison might be to compare 60# and 70# peak weight bows (all else equal).

That begs the question of whether a 70# bow backed off to 60# would generate the same speed as a 60# bow maxed out (all else equaly)? I would doubt it, but have no data to support that either.

There is actually a post I will try and find on archerytalk where a guy did this exact test, same bow type exact same arrow and he got the exact chrono reading( within a few fps) average.
 
It used to be (in the pre-parallel limb days) you would lose both poundage and draw stroke by backing out the limb bolts, so you were in essence changing 2 different variables at the same time. Part of the speed decrease was related to poundage and part to the change in brace height/stroke. I cannot say whether the same is true with the geometry of today's bows, but a better comparison might be to compare 60# and 70# peak weight bows (all else equal).

That begs the question of whether a 70# bow backed off to 60# would generate the same speed as a 60# bow maxed out (all else equaly)? I would doubt it, but have no data to support that either.

I cant wrap my mind around how changing the pre-load on the limbs 10# would affect draw stroke/brace height????
 
I posted BC (before caffeine), it would ADD to brace height because the limb tips on a non-parallel limb bow would shift back, away from the riser. I used to diddle with this stuff a lot a decade or so ago until I figured out it was mostly mental m@sturbation, and have not done anything with the newer parallel limb designs.

I am not sure what affect it would have on a parallel limb bow. I wouldn't imagine the difference would be more than 3-5 fps, but traditionally bows shot at peak poundage have been more efficient than those shot 10# below peak.
 
I cant wrap my mind around how changing the pre-load on the limbs 10# would affect draw stroke/brace height????

On bows like the Mathews MR series for example as you back the poundage down the brace height will increase. Normally this will also cause the draw length to increase as well so you end up having to shorten it by a 1/2". Now you have two of the same bow both set to 60# yet one will have a 6" brace and one with a 6.5" brace. This is how the power stroke of the bow gets affected negatively by backing a 70# down to 60#.
 
Back
Top