Strike Plates, Spines & Speed

[YosemiteSam]

I recently picked up an entry-level D/R longbow.  It draws 55# @ 28".  I flung some arrows from my 50# recurve and, not surprisingly, they flew showing a weak spine.  Bareshafts landing way right of fletched & even fletched landing right of the point of aim.

After messing around with point weights and doing a little internet "research," I learned that building out the strike plate doesn't just change where the arrow is pointed at the end of the draw stroke, it actually changes the angle that the string acts on the arrow, effectively reducing the amount of deflection imparted on the shaft.  Armed with that bit of archery intel, I slapped on a thick piece of leather to the riser & took a bunch of shots.  Sure enough -- bareshafts and fletched landing together & right where I'm looking.  No new arrows or points needed -- pretty cool.

So here's my question -- did I effectively turn my 55# bow into a 50# bow by doing this?  By causing the string to impart less energy on the arrow (bending it less), did I waste that bit of extra energy that I would have kept if I had the arrows flying off the shelf more centered?  Is my 55# bow now only giving 50#-worth of energy?

An easy way to test this would be to use a chronograph.  But, since I don't have one of those, I'm asking those of you who can probably answer this question off the top of your heads.

Thoughts?

[the rifleman]

Any performance loss should ( at least in my experience), be minimal.  Your bareshafts verify that your adjustment was productive tuning-wise and your hitting where you look.    Id say its win win.  My whitetail set ups are in the low 40# range and w well tuned shafts and sharp broadheads i have no issues.
Ive done a lot of chrono testing, but have not actually tested centershot adjustments.  Id be surprised if youd see more than a couple fps impact.  You may actually pick up a bit of speed ( again 1 or 2 fps) due to the positive impact on dynamic spine, evidenced by the tuned bareshaft.
Even if i lost a bit of performance, I'll take accuracy every time.

[McDave]

A more direct and meaningful answer to your question would be to shoot arrows at 45 or 50 yards using the same point of aim, same anchor, same draw, same everything, except for the sideplate, and see what it does to your POI.  For me, that would mean picking a point of aim about 1 yard over the point I wanted to hit at 50 yards, or about a foot over the point I wanted to hit at 45 yards.  If you had a difference in POI at 50 yards of more than a foot, on average, with and without the spacer, I would say that would indicate a substantial difference in velocity, which would indicate a difference in energy imparted to the arrow.  The further out you go, the more significant your results should be, but I wouldn't recommend a distance so far that you have to hold more than a yard above the point you want to hit.  At least for me, that would make it too difficult to shoot a meaningful group.

[mahantango]

Not at all.You simply tuned the bow and if anything, are getting a more efficient transfer of energy to the arrow.

[Butch Speer]

"Not at all.You simply tuned the bow and if anything, are getting a more efficient transfer of energy to the arrow."

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