Brace Height and Arrow Speed

[leonwood]

How about this, not only should the string push arrow all the way from full draw to the brace height of the bow, the string actually pushes on the arrow a little beyond brace height when shot!  How much depends on how light the arrow is, the brace height of the bow, and the elasticity of the string.

Alan

So to open up another can of worms : if a more elastic string pushes the arrow some more after it reaches brace height how come less stretch string like fastflight are faster the b50? Or would this mean there is an optimal amount of stretch for a string to get this extra push when the string slams home?

[George Tsoukalas]

I just brace my bows at the lowest brace eight at which good arrow flight is achieved. That for me is silent flight where only the back of the feathers is seen.

The only thing to gain, for me, at raising the brace height beyond that, is more wear and tear on my bow.

Lowering it only results in very poor flight.

I think it is amazing that one can make a bow and vary optimum brace height.

Jawge

[Del the cat]

How about this, not only should the string push arrow all the way from full draw to the brace height of the bow, the string actually pushes on the arrow a little beyond brace height when shot!  How much depends on how light the arrow is, the brace height of the bow, and the elasticity of the string.

Alan

So to open up another can of worms : if a more elastic string pushes the arrow some more after it reaches brace height how come less stretch string like fastflight are faster the b50? Or would this mean there is an optimal amount of stretch for a string to get this extra push when the string slams home?

What you gain on the roundabout, you loose on the swings.
Any extra push at the end has already been lost when at full draw the string has stretched slightly so the bow isn't actually drawing as far as it would with a non stretch string.
Del

[PatM]

Would the string stretch at full draw when we already know the pressure on it actually drops?

[BowEd]

How about this, not only should the string push arrow all the way from full draw to the brace height of the bow, the string actually pushes on the arrow a little beyond brace height when shot!  How much depends on how light the arrow is, the brace height of the bow, and the elasticity of the string.

Alan

So to open up another can of worms : if a more elastic string pushes the arrow some more after it reaches brace height how come less stretch string like fastflight are faster the b50? Or would this mean there is an optimal amount of stretch for a string to get this extra push when the string slams home?

The mass weight factor of FF compared to B50 makes the diff.

[Badger]

  Exactly BowEd, at the same weight both types of strings perform about the same.
 I think another issue with lower brace heights is that in the final few inches of the stroke the limbs are carrying some momentum that still needs to be sucked out into the arrow. I find around 5" to 6" brace height usually gives me the best results as far as performance goes. I like about 6 1/2 for shooting.

[Stick Bender]

Im wondering if draw length plays a roll in it to ,I draw 30 1/2 to 31" depending on the handle and almost all my natural material bows shoot best for me around 7" give or take for a 32" arrow !

[Selfbowman]

6-61/4brace for me. But I do cut shelf just shy of center. About a 1/8" . This allows a stiffer arrow which has better cast. Need at least 6" of brace even with shelf cut this depth to get the best arrow flight . Hunting arrow or flight arrow. Just my experience. Arvin

[avcase]

Would the string stretch at full draw when we already know the pressure on it actually drops?

Right, the string actually contracts as the bow is drawn. It is the opposite of stretching. It gets shorter as the bow is drawn. This change is greater for more elastic string materials compared to less elastic string materials.

Alan

[BowEd]

So the energy from an overstretched string does'nt get to the arrow.Interesting.

[Del the cat]

Would the string stretch at full draw when we already know the pressure on it actually drops?

Right, the string actually contracts as the bow is drawn. It is the opposite of stretching. It gets shorter as the bow is drawn. This change is greater for more elastic string materials compared to less elastic string materials.

Alan

Errrr.
I think there is some bonkersness creeping in.
If we take it to the limit a near rigid bow and a rubber string (much more elastic).
I think it shows the string stretches.
Del

[Stick Bender]

Here are 4 bows I have extensively tested for for brace height vs speed vs shootability the top down osage leaver bow mild reflex ,BBO Lb ,moderate D/R Glass bow & exstream D/R glass/carbon bow the natural bows both 68" the unaturals both 64"  the 2 natural LB had maybe a varience of 2 fps playing with the brace height from 6-71/4" the trad bows the 64 moderate D/R had a almost non detectable 1 fps & the exstream D/R had virtualy none the trad bows where braced between 7-9" every one of those bows shoot nicer at the longer brace height all where finger realease between 30 1/2-31" varied weights between 48-57lb, ok nothing scientific just a hands on test but to me it seems at least there wasnt enough fps gain to make a difference in a hunting bow they where all shot with FF plus or D97 string !

[BowEd]

Good test Ritch.The results are about what's stated in the TBB.I never have tested that yet.Nice self bow I might add....Ha Ha.

[gfugal]

Would the string stretch at full draw when we already know the pressure on it actually drops?

Right, the string actually contracts as the bow is drawn. It is the opposite of stretching. It gets shorter as the bow is drawn. This change is greater for more elastic string materials compared to less elastic string materials.

Alan

Errrr.
I think there is some bonkersness creeping in.
If we take it to the limit a near rigid bow and a rubber string (much more elastic).
I think it shows the string stretches.
Del

I don't think it's bonkerness, if string tension increases with lower brace heights then it would follow the tension decreases more and more the further the bow is drawn. There was a time where I was trying to figure out at what point the string is under the most tension, and if there was a way to calculate that tension. Long story short it is incredibly difficult physics, with changing vectors, round bending adding near infinate angle and leverage changes, etc. I think theconclusion was that tension at brace was the highest tension, especially when the bow is slamming home but there wasn't a way I could figure out how much more that max "slowing limb momentum" tension was compared to normal brace tension. You would think resting tension would be greatest at full draw, but due to angle changes and leverage the tension actually decreases.

Subsequentaly you can't use the string tension changes at different draws to determine the stress on the limbs. We all know the stress on the limbs at full draw are more than at brace, despite there being less string tension.

[gfugal]

In regards to a bow only pushing an arrow 19" then it would follow that longer draws would shoot at similar speeds as shorter draws, but it is well documented that longer draws, even for comparative draw weights, shoot faster if the bow doesn't get damaged from it. So I think that's hogwash. There might be some truth in it though, that the first inches of recovery accelerate the arrow more than the last couple of inches.