Ideally, since your bow is transferring most all of its stored potential energy into kinetic energy of the arrow, your bow should generate roughly the same kinetic energy regardless of arrow weight within reason. The equation for kinetic energy is given below for both IBO and Real World (rw) arrow flight. Since grains (TAW) are a unit of mass, they can be substituted directly into the equation below.
It is important to note that the number you get for KE using this equation and grains of arrow mass won't result in the normal KE measure of ft-lbs because the grains would need to be converted to slugs for that. If you want the actual KE in ft-lbs for any reason you'll need to multiply the result by the conversion factor 0.00000444 slugs/grain.
Anyway, back to my point, I use this equation to provide an estimated arrow speed for different weights of arrows in my current bow.
If the manufacturer's IBO claims are correct you should get similar results for the same bow setup as used in determining IBO speed. For instance, for my bow at 70#/30in draw and a 350gr arrow Elite claims an IBO of 332-335 ft/sec.
For my 540gr TAW from the same setup the calculation goes like this:
This is pretty close to the 270 ft/sec I've observed with my current setup.
It is important to note that the number you get for KE using this equation and grains of arrow mass won't result in the normal KE measure of ft-lbs because the grains would need to be converted to slugs for that. If you want the actual KE in ft-lbs for any reason you'll need to multiply the result by the conversion factor 0.00000444 slugs/grain.
Anyway, back to my point, I use this equation to provide an estimated arrow speed for different weights of arrows in my current bow.
If the manufacturer's IBO claims are correct you should get similar results for the same bow setup as used in determining IBO speed. For instance, for my bow at 70#/30in draw and a 350gr arrow Elite claims an IBO of 332-335 ft/sec.
For my 540gr TAW from the same setup the calculation goes like this:
This is pretty close to the 270 ft/sec I've observed with my current setup.
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