How draw weight affects arrow speed.

[PennDude]

I'm not sure if this is the right place for this topic so move it if need be.

I'm fairly new to traditional archery, having only seriously started shooting this year. I started with a Martin Jaguar 45# @ 28" and just recently bought a 1970's Bear Grizzly 50# @ 28", which I absolutely love.

Anyhow, I noticed a fairly significant increase in speed with the Grizzly over the Martin Jaguar. Now, I realize they're are two different bows and the Grizzly has a greater draw weight but that got me thinking about how much speed can be gained per pound of draw weight added considering the only thing changing is the draw weight. Bows would have to be the same model, same archer, same arrow weight.

Are there any articles I can read which address this topic?  I'm not looking to just jump into buying a #70 bow, just curious on the topic.  Have any members researched this topic?

[bigb3303]

A 50lb grizzly with a 600 grain arrow will shoot about 169fps, 184fps at 60lb and 200 with 70lb

[Flying Dutchman]

If the only thing you change is the drawweight, your arrow becomes relatively less in weight. The notation for that is gpp which stands for grains per pound.

Suppose your bow delivers 50 lbs at your drawlenght and you are shooting 600 grains arrows. Your gpp will be 12 then.

Now you have the same bow, but with more drawweight, let's say 60 pound, still using the same arrows. Then your gpp will be 10.

So you go from 12 to 10 gpp.

As a rule of thumb, the increase in speed will be something like 5 to 10 fps per gpp less, depending of what bow and drawlenght. So in this example the maximum increase in speed will be 20 fps.

[D.J. Carr]

Use Stu's Spine Calcualator. It will give you your speed.

[Bobaru]

As an academic topic, you can use the responses here as a rule of thumb - and Stu Miller's Dynamic Spine Calculator will allow you to play with all this.

In General, from a practical point of view, as your draw weight increases, your arrow spine needs to increase so that your arrows are tuned.  This will tend to decrease your speed.  

The effect of increased arrow weight with increased spine is probably most pronounced with wood arrows.  

Once you start into these discussions, the whole subject area becomes wide open.  For example, Howard Hill shot powerful bows.  He had a real fight trying to get arrows that were spined for his bows, because wood arrows were the only thing at that time.  His arrows became very heavy and part of the reason was to obtain the spine required.  There are articles written on the compromises he had to make in this regard.

Hope that helps.

[Ravenhood]

I have tested poundage increases with a lot of different bows . 3 pound increase = 5 feet per sec. Its still a guess because I have to use a different bow even though its the same make.

I do not know what the performance of the newer Bear Grizzly would be, but way back in the 70s an area Bear dealer found that the Grizzly was the fastest of the Bear hunting recurves. My own comparison, years later, found that my Schulz longbow was faster than my Bear takedown at the same weight but slower than of the same weight Grizzly.