Effect of limb tip weight on bow speed

[Appalachian Hillbilly]

How much does it effect speed on a bow. I put a new string (X99) and played with brace height and got another honest 5 FPS.

My tips are on the larger, thicker side. Would love to hit 170 at 10 gpp.

[Crooked Stic]

Actually limb tip wedges are meant to keep string angle down.  The ACS was the so called stiff tip without the weight. But if you built in a short lever at the tip can also keep the weight down. A tip wedge of 0- .030 or .040 in about 4 or 5 inches ---- gonna need a chrono to see the difference.
Narrow limb deep core gonna be best anyhow.

[Appalachian Hillbilly]

I don't have wedges in this one. Just wondering if I should lighten up the tips to reduce mass?

[OldRawhide42]

Tape some pennies on the tips and see what it does .

[Longcruise]

Tape some pennies on the tips and see what it does .

I did something similar.  I think I have notes on it on my desktop.  I'll look in the morning.

[Shredd]

Tape some pennies on the tips and see what it does .

 I did that a few years back... I think it was 2 cents on each limb will cost you about 5 fps...

Unless your tips are grossly over weight the weight is not too much of a concern... For an r/d bow I like to keep mine around a half inch and under at the base of the tip overlays... If you are 5/8" and over I can see you to maybe start losing some speed... Whats most important to obtain speed is a nice consistent bend in your limbs... That's why bowyers cheat (if you want to call it that  ) And use tip wedges and power lams... To get that nice bend... For me I like to come off the fades just an inch or two with just a hair less bend and then a consisitent radius about 2/3's of the limb at which point it begins to start straightening out and the last 3 to 4" should be relatively stiff... That is at 28" of draw...  It all depends on your limb design... I seen a lot of guys on the WTT speed contest with bows that appear to be bending a lot more in the first 1/3 to 1/2 the limb with good results...  Looks can be deceiving though... you got to take into account how the limbs were shaped when unstrung and bending at brace before being drawn to full draw... And whether these bows were stable shooting machines or just built fo speed... I tried this style of limb with no success...  Maybe I was missing something that I did not see...  My r/d bows don't look fast with recurves and and such... It is a simple 'D' shaped bow that is vertically stable and has maybe a slight reflex on the last quarter of the limb... But they average 182 to 184 fps and I have reached as high as 187 one time... But then I did some final sanding on the limbs of that bow and lost about 2 to 3 fps... I could have kicked myself... Whenever you make the fastest bow of that design that you ever made... Don't change a thing other than some finish sanding... You want to research that bow and see why it is a bit faster... This is a perfect example that tip weight is not the most important thing... The tips on that bow were a hair on the wide side... I thought I would sand them down and gain an extra 1 to 2 fps, making them 188 to 189 fps...  Instead, I lost speed...

   Here is a tip for you... Visualize a good casting, stout 10 to 11 foot surf rod and what it looks like when casted... Now visualize changing it so it bends more or less at the base and mid section of the rod and also in the tip area... Visualize casting that rod and how it is now bending funky and you are losing distance on your casts...  Now visualize the good rod and reverse engineer it into making a better bow limb... Visualize casting that arrow...     Bending too much at the base of the limb and you have less of a working limb and are having to move all that dead weight on the last half of the limb... Bendind to much at the tips and it begins to stack early and the tips are too thin and whispy to put good power into casting the arrow...

  Hope that helps you...

[4 point]

Shredd, did you notice if the extra tip weight increased hand shock?

[Shredd]

Shredd, did you notice if the extra tip weight increased hand shock?

 

[Kirkll]

The tip overlays could feasibly cost you a few feet per second if the preload was marginal. That preload is determined with the limb design and the wedge locations, and working limb length and location.

Killing hand shock and increasing arrow speed is all about stoping the forward motion of the limbs dead and transferring that energy to the shaft. Keeping tip overlays reasonably sized will help, but it’s not the answer.

Part of the equation that is rarely discussed with limb design is limb travel distance. The less limb travel you have, the easier it is to stop the limbs momentum build up. …… something to think about….  Kirk

[Appalachian Hillbilly]

Funny you mention tip travel distance and speed / handshock.

One of the ideas swirling in my head and been doing some sketching on paper is possible effect of the limb travel distance and speed. The same draw length but different limb designs with different hinge points and different tip travel distances.

My initial thinking is more travel, more speed.

I took my recent 3 piece build to club nigh and had a good friend who has a 30.5" draw shoot it. He said it had some hand shock. I notice very little at my 27-27.5" draw.

I changed the string from a B55 to a X99 string and it seems to have eliminated all handshock for me. I know it has changed the vibe pattern, but I feel the no stretch string are deader than the bouncy B50, B55 variants.

Then I let a compound shooter have a try with it... unbeknownst to me, he was a former bare bow dead eye and he broke one of my arrows by hitting it with his third shot in the same group. Shoots it better than I do...

[Flem]

Part of the equation that is rarely discussed with limb design is limb travel distance. The less limb travel you have, the easier it is to stop the limbs momentum build up. …… something to think about….  Kirk

If thats true, then a smaller string angle at full draw would indicate a bow is potentially more efficient, like this;

[Longcruise]

Its difficult to calculate the distance that the tips will be traveling from that picture. 

[Longcruise]

Well, I found the notes on the shooting done with weight added to the tips.  Here it is.

----------------------------------------------------------------------------------------------
Bow Tip Weight

An experiment to determine the speed effect of adding weight to the tips of a bow.

Bow:

ASL  66” NTN
Slight string follow
44# @ 28”
This bow has no tip overlays and pin

Weight was progressively added to both bow tips and the arrow speed checked with a chronograph.  The weight was added by taping quarters to the tips of the bow.  Each quarter weighs approx 87 grains.
All shots are with the same arrow.  The arrow weight is about 625 grains.  I didn't weigh the specific arrow used but that is in the range of that set of arrows.

First, four shots with no weight to establish a base line

141.8
139.9
137.3
139.5
Avg    139.6


Next four shots were with one quarter taped to each tip of the bow, so 87 grains of additional tip weight.

137.2
139.8
139.6
138.2
Avg    138.2       Equals  1.4 fps slower than unweighted tips

That resulted in such a minor speed difference that I went next to three quarters on each tip for a total of 261 grains of added weight.

138.7
137.9
138.7
137.8
Avg    138.2      This is identical to the speed with only one quarter on each tip.  This is probably explained by the statistical margin of error.

The next increment was four quarters on each tip for a total of 348 grains of added weight on each tip.

137.0
135.5
135.8
137.0
Avg    136.3   Now, we have arrived at a speed loss of 3.3 fps.

And finally, six quarters were added to each bow tip for a total weight of 522 grains of added weight on each tip.  This is in excess of one ounce per tip with one ounce equaling 437.5 grains.

134.1
130.4
134.4
135.6
Avg   133.6   this is a total of 6 fps loss of speed with the 522 grains added to each tip.

Other questions:

Can you imagine the loss of speed that would happen if 1044 grains were added to the arrow weight​

what would be the rate of loss if a much lighter arrow were used?

What would be the results of the same experiment if done with a recurve and various arrow weights

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I've not pursued this any further but I'm tempted to start taping some quarters to the tips of a recurve.

[Flem]

Its difficult to calculate the distance that the tips will be traveling from that picture. 

Same distance, short limbs will get there faster, all other factors being equal.
Take the longest ASL and the shortest Recurve you have and on a tillering board, mark where the string grooves fall when both are drawn to 28"

[Kirkll]

In regards to draw length distance from 28" to 30", the 30" draw will typically be faster with the same gpp arrows.  But as far as limb travel goes, not so much. It's all about stopping those limbs dead and transferring the energy to the shaft.

My Sasquatch  hybrid design only has 3" of limb travel at 28" draw, and 3.5" at a 32" draw and they perform well.

In seriously low preload conditions like an HH D shape with straight unstrung bow profile gives you, or even a string follow bow, the long limb travel could be beneficial with heavy arrow shafts.....

But i've never actually tested that theory...... But It may explain why some guys have actually shown a slight increase of 2-3 FPS in self bows & ASL bows using a B-50 or B-55 string.... That one still bends my mind how you could possibly get better performance using a dacron string, but i've had several guys swear it was true.

[Kirkll]

Long cruise Quote:
"Can you imagine the loss of speed that would happen if 1044 grains were added to the arrow weight?​

what would be the rate of loss if a much lighter arrow were used?

I think that's where the mind bending results come from. I think you may actually get higher performance with the GPP higher with a bow with longer limb travel and lower preload or string tension at brace.

The tests you have done adding weight to the limb tips took a dive dramatically when the string tension wouldn't stop the momentum of the extra weight. I believe it's possible that same momentum makes the heavier arrows faster at longer draw lengths with more limb travel.     

It doesn't make sense at all, but there is a point where arrow weight can mitigate the preload transfer....

[Appalachian Hillbilly]

This is good stuff!

[Longcruise]

what would be the rate of loss if a much lighter arrow were used?

I think the loss would be at a much faster rate and a greater percentage.  That's something I may play around with when the weather warms up along with the recurve results. 

My take-away was when it comes to ASL style, tip weight is not a "thing".

I'm not on-board with the string tension stopping view.  Maybe I oversimplify but in my mind, the arrow is ever accelerating and once it leaves the string is indifferent to what takes place in the string or what the limbs do after departure.  Or, maybe I misunderstand what you are saying. 

[Kirkll]

You are absolutely right about after the arrow leaves the string, it’s a done deal.

But…… and it’s a big Butt….. it’s all about “When” that arrow leaves the string that dictates how much of your stored energy is transferred to the arrow shaft. I need to share some high speed video I took on a bunch of different limb designs years ago.

Back about 10 years ago I was still in serious mad scientist mode and was testing everything I built extensively. I was scratching my head wondering why two very similar limb designs were getting quite a spread in FPS  readings in the chrono with the same GPP. I went so far as up grading my home made shooting machine to a Hooter Shooter, put a slide micrometer on it to get the same exact draw lengths, and took great pains to measure draw weight and arrow weight very precisely….. I even set up two chronographs in tandem So I know my readings were consistent, and did DFC charts on everything too.

Then I set up a high speed video camera to get slow motion video of what the limbs were actually doing after the shot. THAT was an eye opener….. What I found was the limbs that stopped quicker with less string oscillation and less limb oscillation were the most efficient and fastest bows…..   I had a lot of those videos on Photo bucket and lost many of them when photo bucket went sideways and decided to charge you to view your photos…. That was bad…… but I still managed to down load some of those.   Let me see what I can do about posting some.

The bottom line that I came up with is , the strings with less preload and tension at brace continued its forward momentum a bit further before the arrow actually left the string, but at a much slower speed because the limbs were done with their power stroke, but not stopping clean at brace height. the tips were  still moving forward and oscillating . The stored energy was not transferred to the shaft , but bled off and stayed in the limbs……

With many many tests done, the lighter 8-9 gpp arrows suffered more energy loss than 10 gpp or 12 gpp with lack of preload or string tension at brace.


I don’t do as much testing as I used to after refining my limb designs. It was fun, but very time consuming. I mostly just build bows and go fishing or hunting with my spare time now.     Kirk

[Mark R]

Yea that makes sense to me, never really thought about it, now something else to contemplate on my next one, thanks for sharing Kurt, always great when skilled experienced craftsmen share.