Archery Talk Forum banner

1 - 10 of 10 Posts

·
Registered
Joined
·
619 Posts
Discussion Starter #1
My XV Merlin shoots a conservative IBO of 320fps with an 8 inch brace height and extrapolating its efficiency to determine what a power stroke 2inches longer for a 6inch brace height or 3 inches longer for a 5 it would shoot 350-360 fps. In 22 inches of power stroke it already has the same efficiency as the speed bows so why is the draw so smooth with no aggressive roll over? I would love to see an XV with a new riser that put the same set up two inches foward to give a 6 inch brace, it would then have a 24 inch power stroke. All the super speed bows don't seem more efficient just longer stroked with short BH. Anyone know of a speed bow that is efficiency driven? I would like to see one more efficient than the XV.
 

·
Registered
Joined
·
619 Posts
Discussion Starter #2
This is not bashing speed bows as i have owned 5inch BH bows but i would like to see a speed bow that relied on efficiency to get the speed and not just a long power stroke.
 

·
Registered
Joined
·
2,124 Posts
Interesting

I'm looking forward to what folks have to say on this. You raise a great question.
 

·
Excited Delerium
Joined
·
1,024 Posts
I can't answer your question, but I wanted to comment. Look at the evolution of bows since 1985 or so. When I first started shooting it was wheely bows shooting very high poundage with an overdraw and 2413 aluminum arrows. We were getting close to or just over the 300 fps mark and it was a big deal. These were bows that were 41" ata and 7" brace heights.

Then came some dual cam bows that were fast, with medium brace heights and you didn't need an overdraw, and could shoot 20-25 pounds less draw weight. The down side was the harsh draw cycle and keeping them in tune.

Single cams came along, and the efficiency increased. We could shoot a 7" bh at 70# with a carbon arrow and be right around the 300 fps mark.

Some companies like PSE came out with short BH bows like their Carrera and advertised 320 IBO. I have mine still, and for having a short BH it shoots pretty good.

Now we have binary systems that advertise efficiency in the 80% range and IBO speeds in the mid 300's. In addition they have a pretty nice draw cycle to them too.

IMHO, we've come a long way and it will be interesting to see what's next. I think some companies out there have done just what you asked, increased the efficiency and gained some speed. How many bows are currently being offered with brace heights under 6.75"? I don't know, but I don't think it's too many. I think that's a trend companies got away from, but I don't know for sure.

Just my .02
 

·
Registered
Joined
·
129 Posts
My XV Merlin shoots a conservative IBO of 320fps with an 8 inch brace height and extrapolating its efficiency to determine what a power stroke 2inches longer for a 6inch brace height or 3 inches longer for a 5 it would shoot 350-360 fps. In 22 inches of power stroke it already has the same efficiency as the speed bows so why is the draw so smooth with no aggressive roll over? I would love to see an XV with a new riser that put the same set up two inches foward to give a 6 inch brace, it would then have a 24 inch power stroke. All the super speed bows don't seem more efficient just longer stroked with short BH. Anyone know of a speed bow that is efficiency driven? I would like to see one more efficient than the XV.

Then why doesn't their bow with a 7" or 7.5" brace shoot 330? Different cams? THey look the same.


A BT Tribute with a 7.5 or 7.75" brace shoots 328.

A z28 from elite is rated at 336 for 8" brace.

:darkbeer:
 

·
Registered
Joined
·
619 Posts
Discussion Starter #7
Different riser geometry and limb deflection. The XV is 35inch ATA and has a more parallel limb. It just appears that no speed bow is super efficient but instead relies on long power strokes but i am ready to be contradicted????? That is why i ask the question. The XV is as efficient in terms of power stroke versus power returned as the Monster and X force unless my figures are wrong. I would rather have a bow that was super efficient and lost as little of the energy i put in as possible.
 

·
Registered
Joined
·
552 Posts
I am not sure I understand your whole efficiency statement. With todays technology the efficiency is gained by the designs of the new bows. The cams, parallel limbs, and reflex riser designs are giving more preload to the limbs as well as shorter brace heights. The bow companies are producing more efficient bows and that is why the speeds are increasing. Todays bows also have more available power to use in their designs.

You mention your XV with IBO of 320 and a 8 inch brace height being more efficient or matching todays bows? Then you say just make the XV with a 5 or 6 in brace height, well how are you going to do it? In order to have the XV with a shorter brace height you will need to redesign the cams, limbs, and riser!

Just to match your efficiency statement with power stroke, here is what I get out of my X-Force 2007:

28" draw length
60# draw weight
6" brace height
22" power stroke
321 fps

As you can see I am getting a faster speed than your XV with a lower weight and shorter draw length. I would say that is more efficient!
 

·
Registered
Joined
·
2,919 Posts
these discussions of "efficiency" often get confused due to misunderstanding of what it means --

Efficiency = Energy out / energy in, expressed as a %

for a bow, energy out is the KE of the arrow as it leaves the bow; energy in is the area under the force-draw curve (both measured in foot-pounds)

So a slow bow can be efficient or a fast bow can be efficient; it has nothing to do with harshness or smoothness of draw, or power stroke -- it is simply how much you get out as a fraction of how much you put in

Todays "speed bows" generally have pretty high efficiency, in the low to mid 80% range ; in addition to storing a lot of energy -- so yes they are all "efficiency driven" though they don't advertise that because nobody would understand what they are talking about; IBO speed numbers make better marketing.

Is the XV Merlin "efficient" ? We cannot answer that question just by looking at its brace height and rated IBO speed. The fact that you say it has a "smooth draw" does suggest that it might have high efficiency; because a "smooth draw" sometimes means "not much area under the draw-force curve" so in order to produce high energy out (IBO speed) with relatively low energy in, it must be relatively efficient.

Smoothness is subjective -- if you took that "smooth" XV and extended the power stroke 2", your arm might not like it and you might not perceive it to be "smooth" any more

To find out if the XV really does deliver outstanding efficiency, you can go to a shop that has a bow force mapper to find the energy in, chrono an arrow to get the energy out, then do the math -- it would be interesting to see what you get; if it is over 85% then it is truly outstanding.
 

·
Registered
Joined
·
619 Posts
Discussion Starter #10
I understand efficiency and the bow is returning over IBO with peep and release loop installed and i dont skimp on serving either. It just struck me that many speed bows have long power strokes but when you look at non-speed bows with shorter power strokes they return high or higher efficiency per inch of power stroke. I would want a speed bow that could return very high efficiency so when advertised as shooting 340-350 fps it did not need a 6 inch brace height. If a speed bow is just about long power strokes and harsh forcedraw curves then i am not interested. I want a bow that is super efficient and i am not saying the XV is super efficient it just appears from its force draw curve that is very smooth (not rectangular) to return a very high proportion of its energy. When i said if it could have a 5 or 6 inch brace height i simply meant a longer power stroke but as has been said that would ruin its design. I want a bow that gains speed by reducing energy lost in vibration, friction and movment outside the dynamic centre of the shot. Many bows seem to be as efficient if not more so than the Mathews Monster and i would be more attracted to it if it relied less on low brace height and more on efficiency. There must be quite a few bows with 8 inch brace heights getting over 320 IBO and if so they are as efficient if not more so than a bow witha 5 inch BH and stiff drawforce curve. It would not take much to bring these bows grips into more reflex and lengthen powerstrokes without altering cam profile (just as longer draw length models do) and you would have a speed bow. I am certainly no expert and just an intersted archer who would like to see speed bows built with more elegant solutions than stacking more inches on the power stroke.
 
1 - 10 of 10 Posts
Top