Drawlenght vs Speed
 

How much difference in speed would a 446gr arrow have at 70lb,
at 30 inch draw vs 32 inch draw at the same draw weight?

RE: Drawlenght vs Speed
 

That depends upon the cam. I would guess about 15 fps.

RE: Drawlenght vs Speed
 

Premire weighted C 1 cam.I would not think it would be that much!

RE: Drawlenght vs Speed
 

Lets say you bow has a 7 inch brace on a 30 inch draw that leaves you 23 inches of power off the cam. 23 inches divided by speed. FPS per inch. Take that number and mutiply by two for a rough estimate.

RE: Drawlenght vs Speed
 

bow 1
bow 2
difference
% change

SE
85.2
93.6
8.4
9.9
Stored energy (ft/lbs)

E
69.6
76.4
6.9
9.9
Kinetic Energy (ft/lbs)

mtm
0.53
0.55
0.03
4.8
momentum (slug ft/sec)

ps
20.3
22.3
2.0
9.9
power stroke (inches)

eff
0.82
0.82
0.0
0.0
efficiency (as ratio)

v
265.0
277.8
12.8
4.8
velocity (ft/sec)

m
446.0
446.0
0.0
0.0
arrow weight(grains)

p
70.0
70.0
0.0
0.0
peak weight (lbs)

d
30.0
32.0
2.0
6.7
draw length (inches)

b
8.000
8.000
0.0
0.0
brace height (inches)

dv
96.0
96.0
0.0
0.0
deviation from ibo minimum grains/pound

at
12.7
13.3
0.6
4.8
acceleration time (milliseconds)

Vm
100.0
100.0


Virtual Mass (100 grains typical)

sep
1.22
1.34


Stored Energy to Peak ratio

sem
0.72
0.72


Stored Energy to max Stored Energy ratio (should be less than .8)


If I use a cam with an sep of 1.22 at 30" and an initial vel of 265 fps I get a 12.8 fps increase in speed. I think akasharkey has it right. BTW the values in the orangish cells are calculated based on the values in the white cells.

RE: Drawlenght vs Speed
 

O.K. that didn't work very well....

If I use a cam with an sep of 1.22 at 30" and an initial vel of 265 fps I get a 12.8 fps increase in speed. I think akasharkey has it right. BTW the values in the orangish cells are calculated based on the values in the white cells.






There that's much better. This is a little spread sheet I have in excel that alows me to quickly calculate the result of a change in set up conditions. You can see the only change in bow 2 was to increase the draw length to 32 inches.

RE: Drawlenght vs Speed
 

So you guys are saying thaT THEIR SHOULD BE AROUND 12.8 FPS
DIFFERENCE IN SPEED?What is Sep? this is matthew weighted c1 cam i am talking about if that helps AnY!

RE: Drawlenght vs Speed
 

Yes, thereabouts... Given the initial conditions that were picked out of the air except for draw length. If you up the draw by 2" that is roughly what would be expected. Sorry for the confusion with my original post. It looked fine before I posted it but it sure got messed up.

I just guessed at the SEP for your cam as I don't know anything about a c1 cam but I doubt there would be too much difference in the speed increase with a different cam. The major change you are talking about is draw length. 2" is a significant change. Notice stored energy increased by nearly 10%. That's not trivial.

Stored energy to peak weight ratio. It is a number that indicates how severly cammed a bow is. An old fashioned "round" wheel will have an sep of about 1.0. A severely cammed modern bow will have an sep of around 1.4.

RE: Drawlenght vs Speed
 

Thanks so much for your help!! I have the bow ordered.I talked with a guy that had the same bow but had a 32 inch draw.He was getting 276fps
with a 441gr arrow.I will be shooting a 446 gr arrow at the same poundage
and same bow,but my draw length is 30 inches!!! The bow has a 9 inch brace height.Accordingto the charts I can find
that arrow I will be shooting should have around 69 ft pounds of energy which should be plenty!!

RE: Drawlenght vs Speed
 

These are some great posts to read. This web sight is very interesting.
D.Parsons your set-up is going to put the hurt on anything it hits. :)Hope you enjoy your new bow. Your arrow weight is almost exactly the same as my arrow weight.I think from all the calculations you have done (which is very respectful)your arrow weight of 445 grains is a perfect balance of KE, momentum, yet still maintains a great trajectory. Your set-up is very close to mine and after all my research I decided on a 443 grain arrow.I guess doing our homework pays off.Best of luck to you.