View Full Version : Can anyone explain what IBO and AMO means?

Hutch~n~Son Archery
01-27-2011, 04:41 PM
Can anyone explain what IBO and AMO means?


01-27-2011, 05:18 PM
That you put in AMO you are pointing to standards of fps once used by bow manufacturers. They don't use either.... Well, you can get AMO, but have to call the factory.

So more or less for speed shooters;
IBO is basically the rule set forth by the IBO, International Bowhunters Organization. Okay, 30" of draw, 70 pounds of draw weight and a arrow weighing 350 grs (5 grs per pound of draw weight).

More or less heavy bowhunter equipment;
AMO was formerly the Archery Manufacturers Association and now the Archery Trade Association. Here, the draw length is 30" with draw weight of 60 pounds and a 540 gr arrow.

Today the IBO has been replaced and is confusing. Now called, ATA.
ATA fps is to be derived from real numbers. Okay, IBO pounds could be that of up to 82 pounds so long as 5 grs. per pound of draw weight was used.
Read link and I'll see what else I can find.


01-27-2011, 05:30 PM
IBO is what bows wish they could shoot, and AMO is closer to what they will shoot. lol Or you could use Sonny's explanation. lol

01-27-2011, 07:29 PM
exactly ehunter, ibo is for manufacture sales not real life hunting cause once you start rigging out your bow thats when it gets real, not what somebody selling a bow says your bow should shoot. hope im not stepping on toes.::

01-28-2011, 07:05 AM
Manufacturer numbers are real, but we have to think of them as a starting point, not the finished bow set up. I would say these IBO and AMO listings are a starting point. Where would you start being there are some 3 1/2 million archers with whatever different number of bow setups?

Again, I thought the ATA fps listing is confusing. As long as you have 5 grs of arrow weight per pound of draw weight what's the problem? Noted in the link was 82 pounds. So what? I mean, there are factory bow of 80 pound draw weight. Hoyt and others offer 80 pound bows! I know for a fact you can get bows of 100 pounds of draw weight.

If you read the replies of the link you would have read of one person relating of REAL numbers. Well, more people do use a draw weight in the 60 pound range. Next real, real is the average male in the United States. He stands close to 5 foot 10 inches tall - so 70 inches tall which is normally that person's wing span. So 70 - 15 = 55 / 2 = 27 1/2" draw length.

I have a Pearson TX4 with IBO rating of 340 fps. As is it has a 28" draw and maxed out at 62 pounds. I have a loop on the string and nothing else. I used a 314 gr arrow - so 4 grs heavier than allowed IBO spec. It chronograph-ed 310 fps.
Using the below rule of thumb for speed adjustment I came up with the following;
310 + 16 (dw) + 1 + (arrow weight) + 20 (dl) = 347 fps.

And somewhere in here I did the same correction for my Shadowcat and came up with 323 fps. Listed is 320 to 325 fps.

Rule of thumb for speed adjustment;
2 fps / 1 # of Draw Weight
10 fps / 1" of Draw Length
1 fps / 3 grains of arrow weight
1 fps / 3 grains of weight on the string

01-30-2011, 05:56 AM
??? Hutch, no comment?

Hutch~n~Son Archery
01-30-2011, 05:43 PM
??? Hutch, no comment?

Well Sonny what can I comment you explained it very well. Left me with no doubt that I got my answer. But is still funny how the bow companies are saying a bow can do such and such a speed at IBO. But the bow doesn't reach that IBO.


01-30-2011, 08:21 PM
Well, Hutch, I'm sort of lost. Most bows set up at the factory will reach or exceed the listed IBO. I exampled my Pearson TX4. Actual listing for the TX4 is 340 fps +. At a factory the bow is virtually a bare bow with some type of rest and some type of nocking point. I've heard a single brass nock, string tied nock and no nock at all. Now the ATA surely has something they all agreed to use in testing. If not, X bow maker would be on the Soap Box claiming their competitor was using unfair tactics.

Slip over to the automobile.
A car manufacturer claims X car will do 0 to 60 in X seconds. I won't question that and people except the claim. But then we put four people in the car, use different tires, X brand gasoline and how fast will the car go in the same X seconds? Better yet, when was the last time you heard X car won't do the claimed speed?

So skimming over some bow sites; Hoyt has the ATA thing, Ben Pearson has IBO and Martin doesn't say either way, but lists 70#, 30", 350 gr.

01-31-2011, 04:11 AM
What would be nice is, if someone would come up with a system that showed a bows speed rating with a typical hunting setup. Say 60 & 70# draw ratings with a 350gr & 400gr. arrows respectively, at 27.5 inches. Peep, D-loop, and string silencers. Limbsavers on the bow. Make one universal rest for testing. That would help put an end to, or slow down, all the "Why won't my bow shoot what the factory says", as well as give us all a better idea of what we can actually expect from the bow in a real life situation. Noone I know of hunts or target shoots with a tied on knock, and nothing else.

01-31-2011, 06:24 AM
It would be nice to see more realistic numbers, but I think bow set-ups are as varied as the people shooting them and regardless of how you rate them, there is still going be that....."Why won't my bow shoot what the factory says"

I expect for most bow shooters it's easier for them to check the bow speed than it is anything thing else they do.....including tune their bow.
They just walk in to a bow shop, shoot a few arrows thru the dealers chronograph and are upset that the mfr lied.
No consideration is given to draw length or weight, or arrow weight, accessories on string, bow tune, or even if chrony being used is right or not.
Not to blame the shooter, they may not know any better. I suspect most don't.

Using another car analogy, and one drivers take for granted as true. Again because most don't known any different and typically don't have easy means (or money) to verify it, is mfr claimed engine horse power.
Factories get their engine rating sort like bow mfr's get their IBO rating. Measured at the crank under controlled environmental conditions with no accessories.......add on AC compressor, steering pump, alternator and related belt drag, change altitude and barometric pressure, connect a transmission and drive line, various differential gearing, and by the time you get the horsepower to the road you've loss 18-22% of what is claimed.

Knowing what loses can be expected, maybe that's a way to determine the ballparkish speed a bow may actually shoot. Take maybe 15% right off the top of what is claimed for a hunting bow, and maybe 10% off when set-up as a target bow??

01-31-2011, 06:35 AM
Noone I know of hunts or target shoots with a tied on knock, and nothing else.

I have a couple set up like that and all 3 of my wifes bows have only a tied on nock point and 1 'eliminator' button below the arrow nock.
(the one 'button' does not change the chrono reading at all!)

01-31-2011, 06:41 AM
Good point. BUT, IBO being in place for so long I doubt a change would come about.

Still, I would go with just realistic draw length and draw weight and be happy. 27 or 28" of draw and 60 pounds of draw weight is far more realistic than what they have now. Speed is the word, so I'd go for a 300 gr arrow.

Okay, all said within this thread so far, no matter what people would complain. Right now the factories are using a base bow. Start adding in X brand of this or that and people would cry; Why'd they use that junk peep, loop material or any other piece used to set the standard.

The Speed Adjustment in my above reply works, if correct information is used. There are programs and archery sites with the automatic work sheets that work if given the correct information.

I can figure it all day and come within reasonable speeds. And again, most bows will do claimed IBO speeds and more. My old 2000 Hoyt UltraTec is listed with IBO of 314 fps and said listed speed was said slow. It will crank 295 fps set to 62 pounds, 29 inches of draw and using a 314 gr arrow.

70 - 62 = 8 times 2 = 16 --- 295 + 16 = 311 fps --- close.
30 - 29 = 1 times 10 = 10 --- 311 + 10 = 321 fps --- over listed IBO.
62 X 5 = 310 grs is desired IBO arrow weight.
314 - 310 = 4 = 1 fps. --- 321 + 1 = 322.
weight on string 22 grs = 7 fps. --- 322 + 7 = 329 fps. for finish.

Now, I tried the next lightest arrow I had made up, 301 grs which is 9 grs too light for IBO specs. Chronographed my UltraTec nailed 301 fps (yes, 301 fps). So 13 grs lighter gave a increase of 6 fps. So dang near 1 fps for every2 grs. of weight. In other words the bow is more efficient than it should be and this a single cam bow. This bow is also finicky. If I let the specs go out velocity drops fast.

Go back in time; Years back it was said to figure 1 fps for every 5 grs of weight. No doubt bows are getting more efficient.

Also must figured each bow is different, ata, limb angle, cam system and whatever. Somewhere within the scheme of things a bow will perform great and at other points the same bow will perform to a lesser degree.

01-31-2011, 07:24 AM
I've kept detailed records on Martin bows I've had set-up for hunting, and numbers I use for my estimating are similar........changing arrow weight being the biggest varying factor on last 3 bows.

10.0 fps = 1" draw length off base 30"
1.0 fps = 3grs added to string
1.0 fps = 4.2grs arrow weight within 6-7grs/lb off from base 350gr
2.5 fps = 1lb draw weight from base 70lbs

01-31-2011, 03:41 PM
ok, not to try to kill this thread, ive actually learned alot reading this little thread. but who really cares about speed? i know, just about everybody. but usually with speed comes noise, the faster the bow the louder it gets, right? id rather have a slower than "average" bow thats as silent as i can get it. as long as im sighted in out to my comfortable range, and maybe one or two more pins, and im decent enough at range estimation(or i have a handy dandy range finder and ive mentally marked multiple markers in my lanes), then it doesnt matter if its shooting 500fps or 220. neither one makes the deer "deader" than the other.

01-31-2011, 06:51 PM
/// but who really cares about speed? //// it doesnt matter if its shooting 500fps or 220. neither one makes the deer "deader" than the other.

Well, speed does have merit.
First, it gives a idea of how much horsepower the bow generates. Whitetail deer are pretty puny animals, but Elk, moose, and big bears need some whomp. This said, big game has been taken with some pretty low poundage bows, but today more than ever putting down the animal quickly and humanely is paramount.

Second, 3D is a game that needs some amount of speed to offset mis-judged yardages. The ASA has a base speed limit of 280 fps and it would be nice to know if after the build of the 3D bow that it would come close to the 280 fps. For local club 3Ds 280 fps isn't all that necessary, but when sanctioned shoots I want the best of both worlds, accuracy first and speed second. And I have competed in sanctioned shoots with bows that cranked as low as 260 fps and held my own. Beyond doubt another 20 fps would have been nice to have.