inches of draw vs F.P.S.

MichaelT. · 10-19-2006, 09:57 PM

What is the numerical advantage of each added inch of draw length in Feet per second.

Like a for instance:

I am drawing 55 lbs.
I am shooting a arrow at 8.6 gpi with a lenght of 29 inches& 100 gr. BH
My draw length is 29 inches

Then say I make my draw length 30 inches.
What does that extra inch gain me in fps?

Justeven a rough estimate would suffice. Not trying to melt the calculator or anything like that.

Thanks

mobow · 10-19-2006, 09:58 PM

7-10 fps. BUT......it's not worth having the incorrect DL....Proper DL is where it's all at.

MichaelT. · 10-19-2006, 10:04 PM

I understand that Mo, I was curious about how much of a disadvantage someone is at with say 27 inch draw , compaired to someone with a 32 inch draw, out of the same setup. Bow, draw weight , etc. Curious about where some people get their speed out of their bow.

Thanks

mobow · 10-19-2006, 10:12 PM

Oh yeah, shorter DL's are slower, the reason being is the cam isn't in it's "power stroke" as long. The longer the cam can roll, the more energy it will produce.

DaveC · 10-20-2006, 06:06 PM

On the last 2 bows that I tried it on one inch = 9fps (with same weight arrow). These were solo cammed bows, I'm not sure what a binary or twin cam will do.

BGfisher · 10-20-2006, 06:55 PM

Mike,

It's me again, Barry. I'm one of those poor soles with a short draw--27". I don't feel hampered anymore. I'll tell ya what I have done to get more speed besides the obvious things like keeping the string clean, shooting lighter arrows and such.

The most important thing I found is to look at bows with a high IBO speed rating. Prime example is the 2004 Martin SlayR I had. IBO is 325 fps. Of course I wasn't ever going to see that. What I was able to achieve was speeds of 299 fps shooting it for 3D and 280 fps in hunting trim. This with only a peak weight of 53#---and 27" draw.

So I now know it can be done. It does take some time and thinking. For me tinkering is fun. I like changing things and ripping an arrow or two through my chrono to see what happens. Some little things like just changing string material or number of strands can sometimes gain 10-12 fps.

But it all boils down to a bow that has a high IBO rating. Ya have to start with the basics.

Dairy King · 10-21-2006, 01:18 AM

Take your draw length, and subtract your brace height. That give you your powerstroke. Now, take your speed now, and divide it by your powerstroke, this give you your fps per inch of draw.

For me example. 26.25inch draw length, with a 6 inch brace. 26.25-6=20.25........242/20.25=11.95fps per inch

Sniper151 · 10-21-2006, 07:01 PM

Longer draw length will increase kinetic energy but not necessarily speed. A longer draw length will require a stiffer spine arrow and added weight. A archer shooting a 28" arrow at 65 lbs. will have a faster arrow speed than a person shooting a 32" arrow at the same weight, but the longer draw will have the advantage in kinetic energy.

BGfisher · 10-22-2006, 04:37 PM

Quote:

ORIGINAL: Sniper151

Longer draw length will increase kinetic energy but not necessarily speed. A longer draw length will require a stiffer spine arrow and added weight. A archer shooting a 28" arrow at 65 lbs. will have a faster arrow speed than a person shooting a 32" arrow at the same weight, but the longer draw will have the advantage in kinetic energy.

Not necessarily so. Longer length may need a stiffer spine, but the stiffer arrow may not necessarily be heavier. It could be a different arrow altogether. Larger diameter and thinner walls (carbon or aluminum doesn't matter). So the stiffer arrow could be cut and/or adjusted for the same mass weight. That's the only way you can compare the results of a longer draw length. Regardless of what arrow is used in either length it's mass weight has to remain the same.

nubo · 10-22-2006, 07:16 PM

I have a short 27" draw as well ,but I'm not sweating it ,my bow shoot's awsome anyway's maybe not as fastr as some ,but definately fast enough.
I agree approx 10 FPS ,but if your extending your draw lenght in order to get more speed ,then your gonna give up accuracy .I'd definately take accuracy over speed .I've removed as many thing's off my string to make up for some lost FPS ,but I'm shooting dart's at 40 and 50yrds . I've been shooting 28" the past couple seasopn's and haven't been able to be consistant in accuracy ,but now that I'm where i should be ,this bow is now a deadly weapon.

nubo