Same type bow @ different # = Different FPS???

[Zradix]

Hello all!!

If you have 2 bows of the same type ,say two Super Shrews, and one is 45# and the other is 65#. Then you take arrows that are the same grns/# for each bow and shoot them (say 12g/# so a 540grn arrow for the 45# and a 780 grn for the 65#).
 Have the strings be comparable in each bow (few less strands in the 45 few more in the 65 all same material).

Same draw etc..Everything as close to the same as you can get between the 2 bows except the draw weight.

Will one bow necessarily shoot faster than the other??

Thank you

[robtattoo]

Theoretically no, they should both shoot the same. However, all bows have their own little 'quirks', so don't expect identical results.

[Raging Water]

Can anyone here do the math? I can't.

[Chris O]

I saw under the impression that each bow will have its ideal arrow weight which may not be 12 grains per # for both. That would be the only suggestion as to why they could be different.

[Matty]

:confused:  
Call me the odd duck... But Am I missing something major here?
Iv'e read this question numerous times. 2 identical bows with a difference of 20# draw weight will one shoot faster than the other...
I have 2 Super shrews 7# difference between both with matched arrows of close to 10- 12gr /#  the Heavier one shoots 15 FPS faster... Seems like a no brainer....
NOW..Different bows,(ie,pronghorn vs. Shrew) Of different weight, same length, Matched arrows, I have seen considerable differences FAVORING THE LIGHTER BOW. Or the Lighter bow shot faster than the heavier one..
But seriously I'm probably missing something...

[Flying Dutchman]

If everything is identical and you are shooting the same gpp, there will be no difference in speed.

[Raging Water]

F = MA (Force = Mass X Acceleration)

A = F/M (Acceleration = Force divided by Mass)


Force 45# / Mass 540grn arrow = X

Force 65# / Mass 780 grn arrow = Y

[Steelhead]

I once heard that bows as they get heavier loose some of thier effeciency.Like above 60#s or so.I dont know if its True?But if it is I would bet on the 45# er.

[eric-thor]

im with robtattoo.  

[hybridbow hunter]

two bows identicaly built but with different # should have the same dynamic efficiency thus the same gpp arrow speed but, to make a heavier bow, you add more weight in the limbs, you may have a different strand count in the string etc...so dynamic efficiency and the store energy per pound  of draw force (SE/PDF) may not be exactly the same.
Another point is you may feel shooting the 2 bows at the same draw lenght but on the lighter you may have a more dynamic release that could modify the results.
I my experience for the same GPP i found most of the time the lighter bow faster.

[Bjorn]

Might as well apply the same principle to cars with similar success.
The answer is likely 'maybe'.

[Jim Wright]

My experience has been practically identical velocity shooting the same grains/draw weight ratio. the difference, if any has only been a couple of f.p.s. That said, I am talking about draw weights ranging from 50 to 58 lbs.

[Ragnarok Forge]

Theoretically yes they will shoot the same speed.  Now lets throw some physics in to the equation.  Two identical bows shooting everything as noted above will shoot different speeds in most cases.  This is due to variances in the wood in the limbs, efficiency of the bow design, limb shape, etc....  Even matched carbon limbed, aluminum riser bows will often shoot different speeds.

Now throw in the bow weight difference on top of all that and you have another factor added to change the speed a bit more.  The real question to my mind is does the speed change enough to change point of impact of my arrows at hunting ranges.

Simple enough to determine, chronograph both bows with the set ups you noted.  If they are withing 5 fps of each other you will notice very little change of impact point between the bows.  If it is larger than 5 fps.  Fiddle with the arrows on one bow or another until their velocities are as close as you can get them.  Then your point of impact will be the same at say 20 yards.  Just note that the heavier arrow traveling at the same speed will drop off more quickly out past 25 yards or so.

[Zradix]

Ragnarok... I should have said "noticable difference"
I agree with what you said. I thought the 2 bows might be shooting close to the same speed. Just don't have any experience with this.

Thanks everyone.

[SveinD]

This is where Stu's calculator comes in handy!
Typed in the numbers, and as expected, it shows the same speed. Though there will always be minor differences due to the complex and sensitive physics involved, it will most likely not vary more than 1-2 fps..

[John Havard]

If brace height is PRECISELY the same and the strings are PRECISELY the same and if the design of the two bows is PRECISELY the same (like the same model & length of Shrew) and if the draw weights are known PRECISELY and if the arrow weights are known PRECISELY to be the same grains per pound and if you use a shooting machine to PRECISELY draw and release each arrow then yes, the speeds will be the same.  I test bows all the time and have found the above to be true within the accuracy limits of all testing equipment.

[Zradix]

It all sounds reasonable.
Assures me that my first thought was right..nice when that happen once in a while..lol
Thanks everyone!