FDC Graphs of Allegiance vs LX
02-08-2005, 12:50 PM
#11
Thread Starter
Join Date: Nov 2004
Location: Ohio
Posts: 262
RE: FDC Graphs of Allegiance vs LX
Sylvan, we are getting closer but I thought I explained this in my other thread? My Allegiance that I used for the above measurements was measured at 299 fps during the QC testing before BowTech shipped it. They give you a card called a "birth certificate" that shows actual performance of your bow at your DL at 5 grains per lb. of draw weight. The only calculation I did to arrive at 304 was to add 5 fps to simulate removing the 4 rubber silencers on the cables and string. Yes this number is based on the mfg. data but guys like Buckeye, WWAG, and others have verified their bows are shooting within 0 or 1 FPS of the Birth Certificate data from BowTech.
I do understand your skepticism of published speeds from the manufacturers. I can tell you that from my testing Mathews bows are usually 5 to 10 fps slower than the IBO they publish. They do not, however, measure each individual bow like BowTech does. I will find a chronograph, remove the peep and silencers, and shoot a few arrows to verify my numbers. I am confident it is within a few fps if not right on.
I do understand your skepticism of published speeds from the manufacturers. I can tell you that from my testing Mathews bows are usually 5 to 10 fps slower than the IBO they publish. They do not, however, measure each individual bow like BowTech does. I will find a chronograph, remove the peep and silencers, and shoot a few arrows to verify my numbers. I am confident it is within a few fps if not right on.
02-09-2005, 04:43 AM
#13
Boone & Crockett
Join Date: Feb 2003
Location: Lehigh County PA USA
Posts: 12,157
RE: FDC Graphs of Allegiance vs LX
PABowhntr, the DL is AMO, see my correction post above. The area under the curve is the "stored energy" in ft.-lbs. This stored energy is from brace height to the full draw length. Are you asking for the area under the curve just in the locations you mentioned? If so then:
- from 11 - 18 inches on the Allegiance the stored energy is 37.0 ft-lbs.
- from 17 to 24 inches on the LX the stored energy is 39.4 ft-lbs.
- from 11 - 18 inches on the Allegiance the stored energy is 37.0 ft-lbs.
- from 17 to 24 inches on the LX the stored energy is 39.4 ft-lbs.
Thanks for the response. What I was looking for was a comparison between the differences in draw weight over those particular spans that I mentioned. For example, lets say that the cumulative draw weight between 11 and 18 inches on the Allegiance is something like this (11= 25 lbs of draw weight, 12=40 lbs of draw weight, 13= 55 lbs of draw weight, 14= 70 lbs of draw weight, 15=70 lbs of draw weight, 16= 70 lbs of draw weight, 17= 68 lbs of draw weight, 18= 67 lbs of draw weight) for a total of 465 pounds of cumulative weight over that span. I would like that number compared to the cumulative draw weight of the LX over the same span of draw length.
Then, take the span from 18 to 24 inches on both bows and compare that difference to the difference between 11 and 18 inches. What I am trying to get a feel for is which bow actually draws more overall cumulative draw weight during the full length of the draw cycle.
Was that confusing enough?
02-09-2005, 06:13 AM
#14
Nontypical Buck
Join Date: Jan 2005
Location: Upstate New York
Posts: 2,435
RE: FDC Graphs of Allegiance vs LX
Sylvan, we are getting closer but I thought I explained this in my other thread?
You did explain in the other thread and I thought that we both understood. When you post AMO speed = xxx as opposed to just speed = xxx there is a difference in meaning. It is common for the purpose of comparing apples to apples to measure velocity under conditions other than AMO and then convert the speed mathmatically to AMO. If you look in magazines selling bows you will find advertisements where they quote an AMO velocity on a bow that is not even capable of being set to AMO conditions. It's deceiving and makes people believe that the bow they are looking at is faster than it really is. You might say I'm being picky but I think it's important to be accurate. (BTW thank you for editing your post to read just speed =)
One last point. The reason I'm picking on the way you calculated efficiency is that you based it on Bowtechs claim and I simply do not believe velocity numbers from any manufacture.
Here's a tidbit from an article in Huntersfriend.com
In fact, we periodically IBO test new bows here at our facility. Over the course of several years and countless dozens of tests, we have NEVER found a single bow which will actually shoot at or above it's advertised IBO speed - from any manufacturer. Admittedly, some manufacturers come closer than others, but in the real world, most compound bows will actually shoot 10-20 fps less than their advertised IBO speeds. And once setup in a typical hunting rig, most will shoot a measurable 30-50 fps less than the advertised IBO speed.
Advertisers are clearly willing to deceive customers in order to boost sales. Money talks! I wouldn't be surprised that some may even post in popular forums.
02-09-2005, 07:34 AM
#15
Nontypical Buck
Join Date: Feb 2003
Location: Oh USA
Posts: 1,584
RE: FDC Graphs of Allegiance vs LX
Sylvan, what BowTech does is actually shoot each bow at the factory. and provide a tag showing peak weight and speed. People can chrono their bow and see how it compares to the BC. The speed on the BC is not the IBO estimated speed, but actual speed for that particular bow.
In looking at the force draw curves, it becomes apparent the BowTech accelerates the string longer through the power stroke. At about 17" before brace, the LX cam is no longer applying energy to the string/arrow. The Allegiance falls off at about 14". This is where I think the E cams gain the efficiency. Especially at shorter draw lengths, and with heavier arrows.
In looking at the force draw curves, it becomes apparent the BowTech accelerates the string longer through the power stroke. At about 17" before brace, the LX cam is no longer applying energy to the string/arrow. The Allegiance falls off at about 14". This is where I think the E cams gain the efficiency. Especially at shorter draw lengths, and with heavier arrows.
02-09-2005, 08:45 AM
#16
Nontypical Buck
Join Date: Jan 2005
Location: Upstate New York
Posts: 2,435
RE: FDC Graphs of Allegiance vs LX
Look guys, all I'm pointing out here is that the IBO standard rating is 70 pounds peak 30" draw and 350 grains. If ALL of those conditions are not there when the bow is chronographed then the measured speed it is NOT an IBO speed. If you, for example, take a bow that is set at 60 pounds and measure the speed to be 280 then you are WRONG if you say the IBO speed is 280! Thats what several people have been doing in their posts including Blodg but Blodg recognized the error and corrected it. BTW, the one birth certificate that I saw posted here showed the speed as an IBO speed and the standard conditions weren't there. Now you are telling me...
Well if it is not an IBO speed then why does the BC say that it is?
The purpose of IBO is to have a stadardized measurement. Its like units. When your talking about the speed of a car you can't use miles/hour and kilometers/hour interchangably though you can convert 1 to the other.
O.K. I'll get off my soap box now, sorry for the rant but I see this alot and its a hot button issue for me. I really don't believe anybody here is trying to deceive anyone (quite the contrary) althogh I belive its common practice for manufacturers.
The speed on the BC is not the IBO estimated speed, but actual speed for that particular bow.
The purpose of IBO is to have a stadardized measurement. Its like units. When your talking about the speed of a car you can't use miles/hour and kilometers/hour interchangably though you can convert 1 to the other.
O.K. I'll get off my soap box now, sorry for the rant but I see this alot and its a hot button issue for me. I really don't believe anybody here is trying to deceive anyone (quite the contrary) althogh I belive its common practice for manufacturers.
02-09-2005, 10:36 AM
#17
Thread Starter
Join Date: Nov 2004
Location: Ohio
Posts: 262
RE: FDC Graphs of Allegiance vs LX
Sylvan, you have some good points and I agree the speed does need to be verifed. I think people are going to continue to use IBO as a slang term to indicate the 70 lbs. and 350 grains for speed at their given DL.
02-09-2005, 10:45 AM
#18
Join Date: Feb 2003
Location: Alvo Nebraska USA
Posts: 2,057
RE: FDC Graphs of Allegiance vs LX
Manufacture's advertized IBO speeds are a standard that we can judge bows by. The IBO standard is a 70 pound bow shooting a 350 grain arrow with a 30 inch draw. The 350 grain arrow equals 5 grains of arrow weight per pound of peak draw weight. An IBO weight arrow for a 60 pound bow would be 300 grains and 250 grains for a 50 pound bow.
This is much the same for AMO standards in that a 60 pound bow is tested with a 540 grain arrow and 30 inch draw. This equates to 9 grains per pound of peak draw weight.
We can all use an "adjusted" AMO and IBO speed to give ourselves an idea of how our bows perform
This is much the same for AMO standards in that a 60 pound bow is tested with a 540 grain arrow and 30 inch draw. This equates to 9 grains per pound of peak draw weight.
We can all use an "adjusted" AMO and IBO speed to give ourselves an idea of how our bows perform
02-09-2005, 01:03 PM
#20
Nontypical Buck
Join Date: Jan 2005
Location: Upstate New York
Posts: 2,435
RE: FDC Graphs of Allegiance vs LX
walks with a gimp wrote:
The IBO standard for velocity is ABSOLUTELY NOT 5 grains of arrow weight per pound peak. The IBO standard is 350 grains. You are confusing the rules of competition with the standard for measureing velocity.
Another quote from Huntersfriend
If you let the mass float around, you don't have a standard. It would be like saying the speed limit varies pending on the horsepower of your car.
The 350 grain arrow equals 5 grains of arrow weight per pound of peak draw weight. An IBO weight arrow for a 60 pound bow would be 300 grains and 250 grains for a 50 pound bow.
Another quote from Huntersfriend
To really compare two bows, we need an "Apples-to-Apples" method of comparison. Since it wouldn't be fair for one manufacturer to test and rate their bows using one standard, and another using a different standard, manufacturers generally rate their bows using the same IBO (International Bowhunting Organization) Standard. To get an accurate IBO Speed rating, manufacturers must test their bows under the same preset conditions: setting the bow for exactly 70# Peak Draw Weight, exactly 30" Draw Length, and they must shoot a test arrow that weighs precisely 350 grains. Fair enough!