Page 1 of 2 12 LastLast
Results 1 to 6 of 8

Thread: Riser Deflex vs Brace Height

  1. #1
    In the Black
    Join Date
    Mar 2008
    Location
    Canberra
    Posts
    51
    Thanks
    0
    Thanked 5 Times in 3 Posts

    Riser Deflex vs Brace Height

    I've just managed to confuse myself about the effect of riser deflex on brace height. I own a Fiberbow, which is generally stated as having about half an inch of deflex compared to 'normal' risers and it is also said that this means brace height should be half an inch more than for a normal riser. i have just measured the riser and a Samick Masters riser and found that the pivot point of the grip on the Fiberbow is about 10mm closer to the line between the limb pockets than is the case for the Samick. This is consistent with the Fiberbow being more deflex than normal.

    Now, since brace height is measured from the pivot point to the string, and the pivot point is clearly closer to the string to start with, then surely the brace height must be smaller, not larger for a deflexed riser assuming the same limb angles.

    Am I on the wrong track with this? Is the extra brace height meant to somehow compensate for the deflex distance?

    Any help would be appreciated before I start making new strings to get the 'right' brace height.

  2.  

  3. #2
    It's an X
    Join Date
    Mar 2006
    Location
    Poole uk
    Posts
    21,406
    Blog Entries
    1
    Thanks
    4
    Thanked 1,018 Times in 931 Posts
    HI, I am not clear how you measured the line between pockets and pivot and what you mean by "closer".Perhaps I can clarify this for both of us.
    If the Fibrebow is 1/2" more deflex than the Samick, then the grip pivot point will be 1/2" further forward compared to Samick.To measure that, you could draw a line from pocket to pocket on each riser. That line would need to be from the same part of the pocket in both risers and the best place would be where the limbs exit and on the string side of the limbs. Let's assume you did that.
    The next variable is the angle that the limbs exit the risers. If the limbs exit at different angles compared to one another, then the distance from the line of the string and the pivot would also vary. To check that, you could measure from the string to the limbs where they exit the riser.
    Now, since brace height is measured from the pivot point to the string, and the pivot point is clearly closer to the string to start with, then surely the brace height must be smaller, not larger for a deflexed riser assuming the same limb angles.
    Deflex means bent so the pivot is further from the string line than straight riser. Reflex, means bent the opposite way, so the pivot is closer to the string line than a straight riser.It sounds like you have those two mixed up in the quote above.

  4. #3
    In the Black
    Join Date
    Mar 2008
    Location
    Canberra
    Posts
    51
    Thanks
    0
    Thanked 5 Times in 3 Posts
    Geoff,

    Yes I did measure as you described, the only thing I couldn't measure easily was the limb angle emerging from the pocket.

    Maybe part of my confusion here comes from which way is the 'front' (I believe it is towards the string by the definitions I've seen) and also the definition of deflex, which I read in a Hoyt document means in the extreme that the pivot point is in front of the line between the pockets (ie closer to the string). For a recurve, which probably couldn't be constructed to be a full deflex, then I interpreted my measurements as being consistent with discussion about the Fiberbow being deflexed by about 1/2 inch on a number of forums. In those discussions they then go on to say that this means brace height should be increased by the same amount.

    I normally just experiment with the number of twists in strings to get best brace height, but now have a new set of Border Hex 6 limbs needing longer than normal strings and lower than normal brace height, so I'm trying to get a feel for how far I should go relative to recommended heights on a 'normal' riser.

    For example, if recommended brace height is 7 1/2 inches, should I be aiming for 8 inches, or is it 7 inches assuming I have 1/2 inch of deflex?

  5. #4
    It's an X
    Join Date
    Mar 2006
    Location
    Poole uk
    Posts
    21,406
    Blog Entries
    1
    Thanks
    4
    Thanked 1,018 Times in 931 Posts
    If you think of a re-curve limb when in place, the curve is the same way as the Re-flex riser would curve.
    All other things being equal, the defex riser would move the pivot away from the string and increase BH.
    Limb angle is not easy to measure and the amount of bend on the limbs doesn't always stay the same riser to riser, using the same string.
    I guess it would be possible to make a string for each riser that just takes up the slack. Then measuring from string, to exit point of the limbs from the pockets, would indicate which angle is more backwards facing.( facing towards the archer in normal holding bow posture.(undrawn)
    I guess most of that is academic. What really matters is the amount of bend put into the limbs when strung.Too much could over load them on a long draw length. Too little and the limbs may be close to being loose.
    I don't know very much about individual limbs or risers, so I can only give a general sort of response to the questions you asked. If it is about Border limbs, then Border Bows are the people to ask; Sid is on here as BorderBows.

  6. #5
    In the Gold Ar-Pe-Lo's Avatar
    Join Date
    Jan 2010
    Location
    London
    Posts
    815
    Thanks
    9
    Thanked 56 Times in 54 Posts
    don't forget if you mesure FB it is about 1" longer than other risers (windstar and Inno in my case) between limb bolts.......

  7. #6
    In the Black
    Join Date
    Mar 2008
    Location
    Canberra
    Posts
    51
    Thanks
    0
    Thanked 5 Times in 3 Posts
    Thanks guys,

    I may be starting to understand, helped a bit by some words about the new Hoyt riser which say it has 0.7 inches less deflex than the previous model and should gain a bit of speed because this increases effective draw length. From that, and Geoff's explanation I now think that all risers are deflex, some more than others. Reducing deflex moves the pivot point closer to the string and so reduces measured brace height and increases draw length.

    For my Fiberbow I think this means that from my measurements it has less deflex than other risers I have measured and I will correct for this when comparing measured brace height on this riser to others, but will use normal tuning methods to get the best setup regardless.

    As an aside for Ar-Pe-Lo, I've measured the centre to centre distance between limb bolt holes on three risers and found that the Fiberbow is 20mm longer than a KAP Winstar and 7mm longer than a Samick Masters, so maybe KAP/W&W risers are short.

Page 1 of 2 12 LastLast

Similar Threads

  1. Brace height
    By bristol bowmaker in forum Traditional Bows (Archive)
    Replies: 3
    Last Post: 08-01-11, 02:24 PM
  2. brace height help
    By sonkintom78 in forum Traditional Bows (Archive)
    Replies: 1
    Last Post: 19-06-10, 11:29 AM
  3. Brace height
    By BorderBows in forum Recurve Bow
    Replies: 27
    Last Post: 19-04-08, 10:41 AM
  4. Very Low Brace Height
    By Big Boy Blue in forum Recurve Bow
    Replies: 5
    Last Post: 23-01-06, 03:36 PM

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •