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赛
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Discussion Starter #1 (Edited)
How many FPS does a "flexible" riser contribute to arrow speed? I'm saying this only partly in jest: an ultimately stiff riser has to suck up some of the stored limb energy and, not being flexible, has no way of releasing it. Curious is any comparative studies have been made with regard to this corner of bow fizzicks.

Is there a Golden Mean in the balance between flexibility and rigidity?

Regards,

Salskov
 

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My first pure guess...is that any flex given by a riser would take way atleast as much from what the limbs were supposed to be doing, without any benefit manifested in cast of the arrow. Again, just my guess

Atleast for a 3 piece configuration...
 

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Stiffer risers are faster. All the mass of a flexible riser won't accelerate fast enough to contribute anything to arrow speed.

-Grant
 

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Here is the problem with testing this issue. I have 3 gold medalist 25". Mount a pair of 35# Samick Extremes. Set all to 35#. Use a hand winch with a compound release. Shoot the thru your chrono.

I get 2fps variances between 3 risers that are the same. I was never able to figure out the variances.

Maybe my $100 chronograph is not sensitive enough.
 

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My gut instinct is that the difference in riser stiffness will be so small as to be lost in the noise of all the other variables in the system as far as arrow speed is concerned.
 

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Barefaced tightropewalker
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This is what Holger aka Stolid Bull had to say about stiffness in risers as applied to string walking recently:

Those modern constructions are optimized for shooting olympic style and even distribution of forces between upper and lower riser part. Stringwalking produces a strong vertical disbalance of forces during shooting, and thus, the risers have to be much stiffer. It is not only torsion, you have to take care of but bending, as well.

It is not the durability of a riser but you will get better grouping with less vibrations. I am not talking about high frequency vibrations. What disturbs an arrow at release are mid frequency vibrations which are not in phase between upper and lower riser part.
 

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赛
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Discussion Starter #9
I have tested it with an all phenolic riser that was flexing in the grip at full draw. It was 5 fps slower then an all wood riser that was identical with the same limbs.

Mike
Interesting. Although apples/apples are nearly impossible, have you tested wood and metal risers of similar geometry (i.e. length, limb pad angle, deflex, weight and balance) set up with identical limbs, string, etc. ?

Regards,

Salskov
 

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Yep,

Good old Sir Isaac..

F=MA

Also,

Any riser that does not flex, cannot absorb/store enegy.

Simple matter of physics.
The riser doesn't need to flex....The limbs store the energy needed to propel the arrow...In the case of a three piece take-down bow, riser flex isnt much of a good thing...Jim
 

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It's not just F=MA.

The big issues are modulus and elasticity.

The riser is going to be high modulus with a low elastic limit. Limbs on the other hand are going to be low modulus and high elasticity.

The downside of this is that the arrow will be long gone before you start to get elastic effect from the riser. The only impact you are going to see from riser flex is from changing the geometry of the limbs. Therefore a stiffer riser will be faster because more of the draw energy is stored in the limbs (with their high elasticity) rather than in the riser (with its low elasticity).

It's been 30 year since I studied materials science but go look up Young's modulus and Hooke's law.
 

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The riser doesn't need to flex....The limbs store the energy needed to propel the arrow...In the case of a three piece take-down bow, riser flex isnt much of a good thing...Jim
Precisely my point.

Original question was "How many FPS does a "flexible" riser contribute to arrow speed? "

Answer:

Nothing.

A flexing riser detracts from arrow velocity, as less energy would be stored in the limbs.
 
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