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Discuss Question about Hoyt Formula Limbs and Geometry at the Recurve Bow within Archery Interchange Forums; Hi All, New here so hope I'm doing this correctly... I have been shooting my ...
  1. #1
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    Question about Hoyt Formula Limbs and Geometry

    Hi All,
    New here so hope I'm doing this correctly...

    I have been shooting my HPX and 720 limbs for a number of years quite happily. However, recently I have undergone some coaching with significant changes to my form, and feel that it might help for me to drop down to a slightly lighter poundage to work these changes in correctly. I currently have a set of short 720s marked at 42# and measuring around 41.5# on the fingers with a bow gauge.

    There are a set of second hand short F4s for sale in my club, marked at 36#. I am told that sticking to short limbs is a good idea so that the string geometry on the face remains the same. However, this is a fair weight lower than what I am on at the moment (6# less).

    Having done a bit of reading on here I have found people saying that due to the deflex geometry of the HPX, you actually get a couple of pounds more out of the limbs than what they are rated at, and also that they advise people to get a slightly longer bow than normally suggested as the HPX can experience earlier stacking due to similar effects. Firstly is this correct, or just hearsay? I was people could tell me more about this. I shoot 28" arrows, but my measured draw length is actually more like 27-27.7" (arrows are a little long). As a result should I perhaps be considering medium limbs? I have attached a photo of my current (short) top limb at full draw and it looks OK, but I'm no expert here...

    I was also wondering how the F4s might compare to the 720s. For 90m my sight mark is at the bottom of the sight track all the way in. Ideally I would like to shoot a lower poundage whilst training up to 90m. The F4s should be faster than an equivalent set of 720s (foam core vs maple core) I believe, so might I still be able to reach 90 OK if I wound them in (say to 38#)? I know the only way to actually answer this question is to try shooting it, but the thoughts or advice of someone more experienced than myself would be useful.

    Thanks!
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  3. #2
    In the Red Stretch's Avatar
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    Assuming you have a 25" riser you could consider Med limbs but you might lose a few fps doing so. Personally at your drawlength I wouldn't. Looking at the pics the limb looks correct to me. (It may be an optical illusion but the limb looks like it is drawn further in the top picture but both look fine). The limb is opening nicely so you're working the recurve well which is likely to give good efficiency.

    The HPX geometry does add to the draw weight of the marked limb - in theory 1.7# equivalent. But it's the same for both 720 and F4. I doubt you'll see stack (real stack) in the short limb at your drawlength. Put it this way the medium limb is fine on a 27" riser at nearly 32". I think the HP geometry does push the "optimal" length vs draw down a touch. But I'd say it effects the 28.5" draw archery trying to push the 66" bow. If your 720s feel good then stick with what you have.

    With some VERY rough guesstimates -3.5# on your limbs is approx 6 -10 fps in arrow speed. I would be very surprised if the 720 is that much slower than the F4. But you may also need to change to a lighter spine arrow which might offset a little. If you change to Med limbs then I think you'll also lose between 2 and 5 fps. I'd guess you are going to struggle with 90m sight mark until you are back at your normal draw weight. Based purely on product time lines and typical filter down performance I'd expect the 720 to be similar in speed to the F3. The F3 was (if I recall correctly) about 3fps slower than the F4.

    You also need to shoot the F4. If you are used to shooting a smooth woodcore limb like the 720 you might not get on with the feel of the F4. It is a very good limb (Im shot a world record with them at the London Test Event in 2011) but they feel - well a bit plasticcy for want of a better description. The arrow launch is quite aggressive and the noise is more of a crack than a thunk. Mind you I'd say the same between wood and foam core Quattros - just less extreme. (And I have a set of Long and Medium F4s so I'm just saying how I feel about them).

    YMMV and as most of this is guesswork it may vary a LOT!

    Stretch

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    In the Blue

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    I would say if you are seeing the marked draw weight on your scales at your draw length, then there is no issue with them stacking.... Personally I wouldn't be too concerned about shooting 90m with your lower poundage limbs, as I would be looking at shooting short distances only until my form changes were sorted and I was ramping back up to my comp weight limbs. Shooting short distances lets you concentrate on your form rather than drifting int over aiming or getting carried away with scoring.

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    Thanks for the info guys, I decided to go for it and they're already here!

    I haven't redone any setup yet (that's today's job) but stuck them on last night and had a quick shoot.
    My first impressions were that they were very smooth to draw, and felt like they stayed more smooth all the way to the clicker.

    I'll probably come back here after I've shot them a bit to let you know how I'm getting on.

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    In the Red Stretch's Avatar
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    Good luck and enjoy. Like I said it is a very good and under rated limb. Once you hit. 698 for a 720 you know you could be approaching their limits!

    Relative smoothness is not really relevant when you have a big weight difference (unless the limbs are planks) but glad you like the feel.

    I don't remember having any specific tips for the F4 - I have a recollection of being pretty rigorous over deciding tiller and nocking point but probably no more than usual :-) other than that I found them pretty easy to get along with. They were certainly easier to setup that the HDS TX990 which was its predecessor. But the. I think the formula RX is easier than the Helix so some of that could have been riser related.


    Stretch

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