can three knock on a string improve bowspeed?

[sambow]

I recently bought a second hand compound bow. When looking at the bow I noticed three brass knocks fitted to the string a few centimeters up from the lower cam. When I enquired why they were there I was told they increase the bow speed.

I thought no more of it until today when I was watching my lad shoot. I noticed his Hoyt Rintec which he purchased new from Quicks earlier in the year had a bulge in the string just above the lower cam. On closer inspection it was three brass knocks in shrink sleeving.

Now I am filled with curiousity and full of questions:

• Can three bras knocks on a string really make the bow faster?
• If so why doesn't every manufacturer fit them as standard?
  So
• I believe there is no gain without pain, so whats the downside?

I don't have access to a chronograph so I can't prove or disprove it myself. So does anyone have knowledge of this.

[worthipa]

Originally Posted by sambow

[*]Can three brass knocks on a string really make the bow faster?

No, any increase in the weight on the string will make it slower not faster.

[geoffretired]

Strangely enough, Bowtech use them and call them speed nocks. Mathews also fit them and Hoyt.
Adding weight to a string should slow it down but.....
I wonder if cleverly place weights could possibly cause the string to build up speed at a different rate and give the string a flick at the end of the forward travel, increasing the length of the power stroke. Perhaps the longer stroke tanslates into faster arrow speeds. It's an interesting question.

[sambow]

Originally Posted by worthipa

No, any increase in the weight on the string will make it slower not faster.

Thats always been my belief too and the reason why I have never used brass knocks just three truns of polyester thread instead. But there must be something in this. I don't believe hoyt would go the expense of attaching three knocks and covering them with shrink sleeving unless there was a benefit!

[pyroarch57]

I believe they are there to help reduce string oscillation/vibration.

[worthipa]

Originally Posted by geoffretired

Strangely enough, Bowtech use them and call them speed nocks. Mathews also fit them and Hoyt.

They can call them what they want (and they will!) but adding weight can only make the string heavier and therefore slower, unless Bowtech et al have found a way to ignore the laws of physics ...

Originally Posted by geoffretired

I wonder if cleverly place weights could possibly cause the string to build up speed at a different rate.

You can bet, if that were the case, they would fit 9 or 10 and call them Super Duper Fast or somesuch!

[sambow]

Originally Posted by worthipa

They can call them what they want (and they will!) but adding weight can only make the string heavier and therefore slower, unless Bowtech et al have found a way to ignore the laws of physics ...



You can bet, if that were the case, they would fit 9 or 10 and call them Super Duper Fast or somesuch!

My days of physics are long behind me, but I seam to recall then when it came to moving bodies there were two considerations: inertia and momentum.

I am with you entirely regarding weight on a string which will add inertia which will need to be overcome. But just a thought, the weights are positioned very close to the cams, which is a different proposition to a weight in the centre of the string. The cam is attempting to reel the string into the cam, which in turn is causing the string to shorten and propelling the arrow forward. The weights will initially create inertia, but once they start moving they will have momentum which will assist in their movement like a flywheel does. Maybe and it is only a maybe, this momentum speeds up the reeling of the string into the cam????

[geoffretired]

But, what about the length of the power stroke? Changing bracing height can change arrow speed with on loss/gain in weight.

[Stylisht]

Originally Posted by worthipa

They can call them what they want (and they will!) but adding weight can only make the string heavier and therefore slower, unless Bowtech et al have found a way to ignore the laws of physics ...



You can bet, if that were the case, they would fit 9 or 10 and call them Super Duper Fast or somesuch!

Don't know why, don't know how. Something to do with tension on the string. 1 brass nock = + 1fps. Up to a maximum. Chronograph don't lie.

[archery_mum]

Firstly you need a chronograph to set them up. They work well on some Hoyt bows with cam and a half.

Don't just add them without shooting through a chrono as you can make things worse. However we found that done correctly they add about 6fps and while 1 gives an increase, 2 gives a bigger increase but with a variation between arrows and 3 causes the speed to reduce slightly from 2 but the speed is more stable.

You will also find that sliding them up and down the string makes a difference so finding the right position is just as important.

There is also a slow motion video kicking around somewhere that shows how the string on a cam and a half goes back into the cams much faster and with less oscilation with the nocks in place.

I found they worked very well on my Ultra Elite's and there is more difference with the NANO's and X10's than with my heavy indoor X7's.

You will need to ask my husband watch_man exactly how it is done as he has found different positions are required for different arrows and different point weights.