Estimating arrow speed with 60 lbs. bow based on IBO speed.

[wolf6151]

The Bowtech Patriot Dually's IBO speed is 326-334 fps., but that's based on 70 lbs. pull. Is there any way to estimate the speed of this bow or any other bow for that matter with a 60 lbs. pull? I'm debating getting a speed bow (Dually, Supertec, etc.) in 50-60 lbs. pull and bottoming out the limb bolts and possibly shooting the bow at 60-62 bls. vs. getting a slower smoother drawing bow in 70 lbs. pull. Which would be faster? Is there some mathmatical formula for calculating bow speed at 60 lbs. based on advertised 70 lbs. IBO speed? Thanks.

[BowTech_Shooter]

A 60 lb. bow is approx. 4-6 fps slower than a 70 lb. model. Of course this is using a 5 grain per pound arrow.

Regards, Pat

[Rangeball]

And if you're talking same arrow weight, knock off about 15 fps or so...

[DaveC]

That's a great question, I wish they'd supply that # along with the amo speed.

[pdq 5oh]

My 03 Patriot Dually's BC shows 319 with a 300 gr arrow at 61#, 29". It went 288 with a 375 gr arrow at 57#.

[KBacon]

Using a 300 gr arrow... what would be the speed difference between a 60# model w/ the limbs bottomed out.. vs a 70# model w/ the limbs backed down to the same weight as the 60#er?

[wolf6151]

Thanks for the response. Sorry I didn't clarify my question. I was talking about using the same 350 gr. arrow weight in the 60 lbs. model.

Is this statement true: You generally loose or gain about 2 fps. for every pound of weight that it decreased or increased?

I wish that archery manufacturers would supply arrow speeds based on the same 350 gr. arrow at 60 lbs. I know that this would be above the 5gr./lbs. limit that is put on IBO, but how many people really shoot there bow at 5gr./lbs.. Any arrow that I've ever looked up on an arrow chart would be way over 5gr./lbs. if it's spined correctly for the poundage. Show me a 350 gr. arrow that will be the correct spine for a 70 lbs. bow at 30 inch length of pull.

[nubo]

I was using 28" carbon force 100's and shot 292fps at 60# with my 04 dually.

nubo

[Cougar Mag]

My opinion remains that IBO speed is overdone and overrated. Most manufacturers do not adhere to strict standards when testing a bow to list their IBO speed. Although the advertised fastest bows most times are the fastest bows.

[DaveC]

Wolf, I agree. How about a chart with draw weight on one side and arrow weight on another the intersecting line would be the speed as shipped.

Only problem is deciding on a "average" draw length. I vote 29.5"