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konradlau
09-25-2010, 06:44 PM
Most bow manufacturers’ advertising gives IBO speeds as part of their sales spiel. Most of those specifications cover a range (typically 8 fps) or make claims “up to X fps”.

Given the IBO specifically states draw length, arrow weight and draw weight, what does this range of numbers represent?

Is this standard deviation, extreme deviation or some other range I am unfamiliar with?
If this is "standard deviation", is this measurement taken from one bow or an average of the bows taken from the production line.

Thanks,
Konrad

RobD
09-28-2010, 09:43 AM
I agree with you a 100 %.All companys give IBO speeds.Which in my thoughts, there is no point for it,because there is no possibility.To ever achieve those speeds.Because they get these speeds for a bare shaft arrow exactly the least amount of weight and a bare bow, not even a D loop on the bow. I think it would make alot of people happier to see lower speeds posted for bows.But realistic numbers.I see people get really upset when there bow doesn't even come close to the IBO speeds.But if they didn't do that there would be a lot of companys out of business.

Montalaar
09-28-2010, 10:03 AM
Most bow manufacturers’ advertising gives IBO speeds as part of their sales spiel. Most of those specifications cover a range (typically 8 fps) or make claims “up to X fps”.

Given the IBO specifically states draw length, arrow weight and draw weight, what does this range of numbers represent?

Is this standard deviation, extreme deviation or some other range I am unfamiliar with?
If this is "standard deviation", is this measurement taken from one bow or an average of the bows taken from the production line.

Thanks,
Konrad

It is up to each manufacturer how he gets this speed and how he defines the range he gives. Take Hoyt as an example. You can even exceed their ibo speeds. Or take a look at PSE or Martin. You will propably never get those speed. The reason is that the bow is loaded with a bare arrow, nothing on the string. The drawlength might be up to 30.5" and the draw weight up to 65 lbs. And you can still call it 'ibo speed'...


I do not think that anyone calculates SD or SE for the speeds they use to sell their bows with.

I am pretty sure that they take one bow, tune it to the max and measure the speed. Then they may make a round number out of it and voila. You have the speeds.

b0w_bender
09-28-2010, 02:04 PM
It's my understanding that they do all sorts of temporary things you wouldn't do to a stock bow like put a string on it that has half the number of strands on it, exotic lubrication you name it.

SonnyThomas
09-28-2010, 06:24 PM
This spread, if you wish, is taken from a test, either in numbers or random. Bows are all setup the same, but through limbs and tolerances speed varies. This is not hard to believe. Arrows, whether fletched or bare won't make a that much of difference when the arrow is but one arrow length from the chronograph. Check most manuals of chronographs and you will find the 1 arrow length.

I have this that is a rule of thumb. Some don't understand how it works. For my Shadowcat, 320 - 325 fps, I came up with 322 fps. So within factory given. Figures at bottom.

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.

*A few years back this figure was 5 grs per 1 fps. Figure better limbs, limbs shorter to snap back quicker, cams more aggressive, strings better and more bows with bearings in top wheels makes for more speed.
*Believe it or not there are bows where 2 grs of arrow can give 1 fps.


Bow set to draw weight of 58 pounds, draw length of 28", arrow weighs 342 grs, 18 grs on string.
70 - 58 = 12 X 2 = +24 fps
30 - 28 = 2 X 10 = +20 fps
52 / 3 ======== +17 fps (my arrow being heavy at 342 / IBO wt 290)
18 / 3 ======== - 6 fps (subtraction from speed)
Actually chronograph reading of 267 fps + 61 = 328 fps - 6 = 322 fps.

Destroyer
09-28-2010, 07:38 PM
I am pretty sure that they take one bow, tune it to the max and measure the speed. Then they may make a round number out of it and voila. You have the speeds.

Pretty much I think, might not even tune them, that's why the range. :)