BigJ71

I hope someone can answer this.

My bow has an IBO rating of 290fps. Now as I understand it this is at 70lbs and 30in draw, however my draw is at 32.5in. So with everything else being the same what speed would my bow be at?

I really don't care about the speed, it shoots just fine and penetrates well, I have just always wondered about how many more fps (if any) it would have at 70lb & 32.5in vs 70lb & 30in.

Thanks

Sniper151

You should pick up about 6 to 8 fps. in speed, (about 3 to 3 1/2 per inch) but the kinetic energy you are generating with you long draw length is very, VERY substantial. I'll take kinetic energy over speed any day.

BigJ71

Thanks for the responce,

I used to shoot at 33in (81 1/4in arm spand) but I shortened to 32.5 and it seems to feel better, groups are the same.

The bow has an 8in brace height so I have a 24.5in travel (does tend to build energy!)

BGfisher

I don't know, but all the figures I've ever seen posted have said that 30" is the benchmark. Add or subtract 10-15fps (12fps for average) for each inch above or below the benchmark. My chronograph usually bears this out.

So I'd say you just raised your bow's IBO to 310fps. That probably will mean a real world hunting setup between 250fps and 270fps, depending on your setup.

buckeye

10 - 12 fps is the rule of thumb for each 1 inch increment of draw lenght adjustment.

BigJ71

Thanks for all of the responces,

It was one of those things that I aways wondered about.

I still wonder how they came up with an IBO speed with a bow that has a draw length of 31-33in? Did they test it at 31 and then just subtract approx. 12fps?

Things that make you go Hmmmmmm?

buckeye

IBO speed is only measured at

30 inch draw length
70 pounds draw weight
350 grain arrow

BigJ71

So how do they measure a bow thats draw length starts at 31?

PLB

BigJ12,

You don't!

IBO speed is a standard rating used by most bow companys to compare apples to apples, i.e. if you wanted to compare an Xtec to an Outback (on paper that is) you could check their IBO speeds.

Don't put a lot of concern/thought into IBO speed because it probably doesn't mean crap to you anyway. Not many people shoot a 30" draw and a 350 grain arrow.

Your draw weight, draw length, arrow weight, and various equipment on your bow and arrows for that matter, will effect your personal arrow speed. Take your bow to the local bow shop and ask to shoot it through a cronograph. Then you will know your bow speed.

BigJ71

I'm not looking to find out how fast my bow is.

I just want to know how they measure a bow that has a draw length of 31-33 when the standard is 30? (all things being the same)