Somebody help me understand why....

[SuperK]

Somebody please help me understand why if you put an aluminum footing on a carbon arrow, the dyn. spine increases?  I thought adding weight to the end of the arrow reduces the spine, not increases it.  For example on Stu Millers calulator:
Goldtip 3555 black
27.5 inches
200 grain point
15 grain insert
15 grain nock
3x5 inch feathers=  D.Spine of 60.8
If I add a 2 inch aluminum footing of 25 grains, the D.Spine increases to 72.8!
Am I doing something wrong or what?
Somebody explan this to me....PLEASE!

[njloco]

Wish I could help, but I don't put footings on my arrows.

Sorry.

[Buckeye Trad Hunter]

Because it effectively makes the arrow shorter.  Not by actually decreasing the length but by shortening the amount of the arrow that can flex.

[McDave]

Spine increases as the stiffness of the shaft increases. Spine decreases as the point weight increases.  A 2" piece of aluminum arrow shafting doesn't weigh very much, but does increase the stiffness of the shaft as a whole somewhat by making the front 2" inflexible.  I would assume the increase in shaft stiffness more than offsets the increase in point weight.

[Ragnarok Forge]

I have found it makes no difference in arrow flight unless you shoot short shafts.  I shoot full length shafts and two inches of footing does not impact the spine at all.   With shorter shafts it can have a greater impact.

[wtpops]

McDave and Buckeye hit it on the head, when you add a 2" footing on to your arrow you are making that 2" non-flexable there fore turning your 27.5" arrow into a 25.5" arrow as far as spine goes. The same goes for incerts. The calulator uses the standered incert lenght for its calulations, if you use a long 100 grain incert you need to put the diferance in incert lenght in the footing box.

[gto_guy]

How about adding 1.5 inch footing that`s what I do and spine goes down on stu`s calculator.

[Bill Carlsen]

A 1" footing is all I use.

[SuperK]

Thanks ya'll...now I understand!    

[Guru]

Originally posted by Bill Carlsen:
A 1" footing is all I use.

Me too and I've never seen a bit of difference how my arrows shoot with or without the footing.

[wtpops]

Originally posted by Guru:
 

Originally posted by Bill Carlsen:
A 1" footing is all I use.

Me too and I've never seen a bit of difference how my arrows shoot with or without the footing. [/b]

With a 1" footing you should not see a difference as a standerd incert is just shy of 1" so that first 1" is already rendered non-flexable by the incert.

Just throwing that out there for the guys that might not understand why a 1" footing would not make a differance.

[coaster500]

pops is right even with brass inserts.

If you are using 100 brass inserts you have about 1 1/4" inside the shaft and 1/4" in front of the shaft. If anything with a 1" footing your spine should decrease the tiniest bit due to the extra weight. If you are using 50 grain brass inserts you have 3/4" inside and 1/8 in front. This should cancel out the 1" footing and should make no noticeable difference in spine.

[TroutGuide]

I 2nd 1" footing and no difference.