IBO speed for compounds <70 pounds and <30 inch draw

BrianD3

My understanding of IBO speed ratings for compound bows is they are for bows with:
a 70 pound draw weight
a 30 inch draw length
shooting an arrow weighing 5 grains per pound of draw weight.

Clear enough, but some compounds are not available in 70 pounds/30 inches yet an IBO speed is still quoted. How does this work then? Lets say you have a bow that has max draw weight of 60 pounds, a max draw length of 29 inches and a 280 fps IBO speed - has this speed been measured at 60 pounds/29 inches. Or was it determined by "extrapolating" to the standard 70 pounds/30 inches.

Have been wondering about this for a while.

jonnyarcher

. If ur bow doesnt go to that then u probaly can buy the moduels to make it 30 inch and heavier limbs to make it 70.

BrianD3

Thanks, I am pretty sure that the bows I'm talking about are not routinely available with different limbs and modules. If they are then it would be some sort of custom setup or special order.

Just had a look at some Diamond bow specs, the Diamond Razor Edge model has a max draw length of 29 and the IBO speed is stated as "308 fps @ 29". So that's very clear. Although it's less clear for the Nuclear Ice model, a junior bow with a max draw length of 24
http://www.diamondarchery.com/products.php

The Martin Leopard is a short draw bow and it is stated that the IBO speed is measured at a lower draw length and weight than the 30 inch/70 pound standard
http://www.martinarchery.com/2010web/leopard.php

But it isn't explicitly stated for the Hoyt Trykon Jr
http://www.hoyt.com/compound_bows/hoyt_trykon_junior_compound_bow.php

But based on these examples, I think the answer to my question about extrapolation is that no, the manufacturers don't do this. IBO speed is at 30 inches/70 pounds but if a bow's max draw length/weight are below this, the IBO speed is measured at the bow's max draw length and weight using an arrow weighing 5 grains per pound of draw weight.