Chrono scores

bolerus

Member
Hi guys

I am currently trying to put. Database together (at my club). For limb speeds

So,. If anybody has any chronograph results that they don't mind sharing I'd be very grateful.

Information I'm looking for is
Limb make / model
Limb poundage
Arrows used
Arrow spine
Arrow length
(Weight if known would make life easier for me)
Archer draw length

Once I have finished gathering data (which may take awhile as we have a lot of limbs to shoot the the chrono). I'll be happy to share the v results.

Thanks

Mike
 


Whitehart

Active member
And make sure the arrow spine and bow are set up correctly.... can of worms

Also String material, number of strands, tab make and face material and how good the release is I have seen people lose or gain 4fps with a bad release or good release.

Good luck with getting meaningful data - one of the reasons manufacturers don't publish this data other than this years limb is faster than last years by now we must be up 1000 fps - bit like golf clubs 20 yards each year 20 years we must be over 800 yards by now :)
 


LAC Mark

Member
Thats why i am asking for drawn length, so it can be calculated rather than the usual (about xx on fingers)
How are you going to take into account the tiller bolt position, that can easily be a 10% drift.
10% is a hell of a lot when your comparing limbs for speed.
 


Timid Toad

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And which riser they are on. I can get a 20% difference between the same air of limbs on an aggressive riser and a more moderate geometry!
 


Rik

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Plus variations in chronos and conditions on testing (lighting can be an issue)...
Ideally, you need a reference setup: i.e. This pair of limbs with this handle set to this angle, with this shaft of this weight, and drawn to this weight produces X fps, then measure everything else as a delta to that...
A database might be interesting, but it would only be useful for indicating gross differences. As a WAG, you'd probably have to say that limbs producing results with +-10% of each other were within the error range and equivalent to each other. Unfortunately, I suspect that would include most limbs on the market!
 


Timid Toad

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No, that wouldn't work, because different limbs require different shaft spines/weights, because of their different relative efficiencies.

There's a reason why no one actually does this...
 


bolerus

Member
thanks for all the positivity guys, well appreciated.

jesus I just want to help some of the guys at the club when they start asking the which limbs, including myself, by getting some comparrisons.

SF limbs are X slower than win win limbs of the same poundage
 


geoffretired

Supporter
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I can understand that you want to help the newer members at the club with their arrow selections. I guess that happens at many clubs.
From what you have written in this thread, you are prepared to spend a great deal of time putting some data together to make the advice more useful/more accurate.
It would seem though, that after all your hard work, the results will end up being very similar to using the charts.
There are so many variables that huge numbers of pieces of data would be needed, and I think that is how the Easton charts were produced in the first place.
I think the posts that you have found to be negative, were made to try to save you a lot of effort that could end up leading to frustration.
Even if a powerful computer was used and fed with masses of bits of accurate data, the results would not give a really accurate match because the human being in the equation is also a variable and one that is rarely a "known quantity".
It's like the idea that an archer's draw length can be calculated from their arm span. It's better to watch them drawing a bow properly, than to use data from thousands of archers.
 


Timid Toad

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I think the OP was trying to show which limbs were faster than others, and by how much...not arrow selection.
 


Rik

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It's a nice idea, but there isn't usually much real basis for those kinds of assessments, other than marketing.... Unless there are real design changes and not just a little bit of fiddling with materials it's likely you won't see significant differences in performance between models of limbs around the same price points. Take out glass and replace with carbon, is one of the few I can think of which might be noticeable, other than that, making real differences to draw/force curves...
 


bolerus

Member
Last summer. When I was trying to build my shoulder back up. I bought some SF carbon foam limbs. At 36 lb. Had to put the sight on the inside of the bow to reach 80yards. Took them off and put on friends 36lb inno ex power. Same string. Same arrows. Same day. Same conditions. I comfortably hit 80y. With sight on second hole , out normally..... At 8.5 on the vertical marker.... Loads of room. To drop it.

That is an absolutely massive difference between 2 sets of limbs of the same poundage.


If I had a rough, even rough speed comparison I would not have waisted my money on the SF limbs
 


Rik

Supporter
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Same tiller, same weight on your fingers, correct setup ("tune")...? Unless they are set up equivalently, you're not making a real comparison. Not that I would be surprised to see some differences between a pair of top end limbs and budget ones, just that this illustrates the difficulties in comparison. I can't tell from what you described, if you established a real difference or not. It's just anecdotal.
 


bolerus

Member
Yes the tillers were both eithin accepted tolerance. Brace height were both with manufacturers guidelines

The difference was enormous. The difference between not being able to reach a distance and comfortably hitting a difference.

And that is the very reason that done kind of benchmark is needed.

The problem with archery is their are far too many theoretic engineers. The main reason that an average intermediate archer chooses new limbs is to reach a new distance. Archery shops often have indoor ranges to get a feel and tune etc but how many shops have the facilities to shoot 80yards.

Poundage alone will not tell you if you can reach a specified distance

A rough ( and yes I am fully aware that it will be a rough comparrison and not a scientific true guide) guide to reletive speeds of certain limbs will at least give people a fighting chance
 


Rik

Supporter
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I would not disagree, in theory. But the variation between two of the same sets of limbs may be greater than the average variation between different models. Which still leaves you with a "suck it and see" approach. Manufacturers will not want the variance publicised and are likely to be the only ones with anything like that data.
Any ad-hoc anecdotal database risks being misleading.

Take as another data point: back in the late 80s I shot a bow with sub 32lb draw weight (marked at 32, but my draw is short and they were not adjustable), aluminium shafts and comfortably reached 80 yards with the sight in front. Wood/glass limbs. What does that really tell you...?
 


Timid Toad

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You know it's just as likely that your set of SFs were a set of duds - it happens.
Probably the best way to determine whose limb reaches what distance is to put a poll out: who reaches 80yds with 30lbs/32lbs/34lbs etc and build some statistical averages rather than testing one single set of untuned/badly set up limbs against another. You can then also compile short/medium/long, arrow type/pile weight/length, weight otf etc. That will enable potential buyers to match their abilities with their purchasing power and their physical situation.
 


4d4m

Member
It's not some kind of magical unmeasurable quality; it's just physics.


What dictates the max speed of limb tips? Materials (stiffness of a composite beam), profile (thickness, width, taper), curvature, overall mass and mass distribution (also governed by materials and dimensions). The ideal measure eliminating most possible variables is the limb tip acceleration and velocity curve in thin air when released from a constant deflection, (no string or anything) but that's damaging to the limbs.

So to remove as many other variables as possible: use a shooting machine to remove the squidgy bit (the archer), use a reference riser, string and arrow. Pick (a riser with) typical/standard limb angles, brace height, draw length, arrow mass that are all "middle of the road" of the recommended ranges. Spine? Well my gut feel is that it isn't that relevant for limb comparison purposes. To get the best possible arrow speed (highest efficiency) it should be as stiff as possible for the arrow dimensions chosen, to minimise energy lost to flex.


This gives you a comparative velocity, not a velocity you should necessarily expect in the real world. With the arrow mass and velocity you've got output (kinetic) energy. Measure draw force curve and calculate input energy (area under the curve). You can then get a figure for input energy and hence efficiency. The lost energy is in the kinetic energy imparted to the string and the limbs, any vibration in the limbs, arrow flex, sound energy of the shot, air resistance, and in any plasticity/hysteresis of the limbs or string (permanent deformation, loss of springiness, stretch of the string etc, lost in the form of heat).


In addition to the middle of the road values for arrow mass I'd also pick a high and low mass arrow shaft trying to keep everything else the same and calculate the efficiency for each. In most cases this will be the highest mass as that is able to pick up the most energy from the limbs. So to give the best representation of the potential for those limbs perhaps an average of the three would best.


If you were looking for a topic for a doctoral thesis in mechanics you could then look at deriving formulae to predict this from measurable attributes on the limbs themselves. Plug your data into simulations etc. There's probably a dozen or more of these been done by various people.


I suspect manufacturers know all this but really don't want comparison tables "out there".
 


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