So-called 'IBO speed' is scaled at 30" draw length, 70 pounds draw weight, 350 grain arrow. NO string accessories, not even a nockset. And since it's unofficial andhas no authority as anindustry standard,there is no guarantee that they won't fudge the draw weight or draw length a little bit to fluff up the numbers.

Anyway, less draw weight, shorter draw length, more arrow weight, addition of string accessories (nock set, silencers, peeps, loops, kissers, etc) will all cut down the speed. Often significantly.

Your shooting mechanics can affect speed. If you allow the string to creep forward before you release, you've cut speed off your arrow.A bow's tune will also affect speed. If it's even the slightest bit out of adjustment, it can cause a drop in speed.

If you'd like to see theauthentic, real deal archery industry standard method for testing arrow speeds, it's ASTM f-1544-99. You won't find 'IBO' in there anywhere. Here's a link to it:

http://peteward.com/ASTMstandard.pdf