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#1 Honky Cat

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Posted 30 January 2010 - 08:53 PM

I've asked alot of questions of you nice folks and read some books and articles on bow setup and tuning. It has worked and I am now very pleased with my bow and my ability to hit what I want with it. I never specifically remember anything about temperature changes affecting arrow speed though. It is, however, very apparent in my 40 lb recurve.

Maybe most bows are more immune to this and my $100 recurve is just showing its value. But, I have noticed that during summer practice my third pin is my 40 yard pin. During winter practice my third pin is my 25 yd pin and I have to aim high at 30 yds.

Before hunting, I always string the bow and set it outside a couple hours to match temps. I take a few practice shots before leaving to see where things are going for that temp. I know I'm new and make some mistakes, but I swear that this is for real. I will get very consistent groups that change in elevation due to temperature.

So, what do you all think? I have heard many stories of guys taking shot after shot at deer and missing low. They usually fault themselves as misjudging the distance. Maybe, their equipment was only set up at one temp., then after 2-3 hours in the woods things changed.

I would have assumed that being cold would stiffen the limbs and speed things up, but that's not the case at least with my bow. The way I'm compensating for this change seems to work. I haven't killed a deer with my bow yet, but that's because I'm not very good at getting a clear shot. I would like to hear if anyone else experiences this and how they deal with it.
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#2 Geoff / TBow

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Posted 30 January 2010 - 10:13 PM

HC,
I ain't no engineer, but I have been bowhunting for close to 40 years now and have experienced a good many types of bows made up of many materials. So I'll give my .02 to consider.

Most new compound bow limbs are made of composite materials such as grahite and are typically not laminated. Solid limbs made of materials such as graphite tend not to be affected by variables in temperatures to the degree that wood/fibreglass laminated limbs are.

Most recurves use wood/fibreglass laminated limbs, which would tend to lend them to varying performances as temperatures change. A bow operates on its ability to bend and return to its original position when released. My personal take on wood laminations is that they are more elastic in warmer conditions and able to flex more and faster. Frigid temps tend to make the wood rigid (as it does with any organic material), reducing its ability to flex.

Make sense? Maybe not, but it sounded good to me. Maybe some of the other members might be able to put a little more scientific take on it, but I think I'm on the right track. In any event, don't totally blame your recurve as being of poor quality, it's just the characteristic of the materials typically used in that design of bow. More expensive recurves may very well use more expensive woods with greater numbers of laminations and tuned fibreglass laminations to increase the consistancy during variables. I would also think that a longer limbed bow might be more consistant with regards to arrow speed, while short limbed recurves (48" to 54") would likely exhibit greater fluctuations in speeds as temperatures vary.

Something also to consider is if the cold temps are altering your spline rating of your arrows. Again, the variable will change with different shaft materials. If your arrows become stiffer in colder temps, then their ability to flex (archer's paradox) could also change and cause them to shoot differently.

Geoff / TBow
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#3 Rowdy Yates

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Posted 31 January 2010 - 10:48 AM

Wood will react very quickly to humidity or the dryness as well as temps. The winter air is especially dry compared to the summer humidity. The string on a bow depending on the wax, the type of wax and amount it has or the lack there of it will be affected by this dryness difference.

The sight change is unusual to me. The pin distance to me should all stay relevant to one another at set distances. Now the height change could be the change in the limbs/strings but my thinking the gang change to all pins should be done to the POI. If one changes they all should change equally. Just my .02.

Now I was out practising yesterday in 18*. Sun was out a bit and the air was very dry. My lighter carbon arrows where hitting a bit higher but my heavier arrows where in comparison hitting normally just below those at 20/30/40 yards, broadheads or field points.

Hope that's some help. Posted Image
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#4 Leo

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Posted 31 January 2010 - 12:07 PM

I'll give you some of the engineering take on it.

On composite materials a major portion of their content is the resin used to bind the fibers (glass, graphite, wood). Not all resins are equal! Some of them absolutely maintain their properties at a wider range of temperatures than others. Some resins become extremely brittle at cold temperatures and cracks form at a microlevel when they are subjected to stress. This is a worse case scenario and what you'll notice is the bows loss in power is still evident at the warmer temperatures.

What you also may experience is an increase in hysteresis in the bow limbs at colder temps. Some resins and fiber reinforcements are more susceptible to an increase in hysteresis than others. Essentially hysteresis is a slowing down of the limbs recovery time. This results in a loss of speed.
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#5 PA RIDGE RUNNER

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Posted 31 January 2010 - 02:01 PM

A little something else to think about also is the human body at lower temperatures does not work as well as in warmer temps. You have colder muscles and more clothes on too.
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#6 Honky Cat

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Posted 31 January 2010 - 04:12 PM

thanks for the response. I think I'll put my bets with Leo's, slower limb recovery due to colder temp, theory. I tried to read about Hysteresis on wiki and was left feeling a bit confused. Apparently it is a broad spectrum engineering term used to describe loads of stuff. Elastic hysteresis seemed to fit best so I read that one. If I am understanding corrrectly, As the limbs are flexed they create heat with the elastic potential energy. Some of that heat is dissipated (especially in very cold environments) and the return energy when the limbs are released is less. Most bow designs have probably found ways to minimize this and my thin laminate 40 lb recurve must just be really susceptible to this effect. No big deal, I'll just keep practicing before every hunt. It's a good idea no matter what the temp. is just to be certain there is no other problem with the entire bow.
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