Is there a way to weaken the spine of an arrow without adding more tip weight?  Would adding weight inside help (something like string trimmer line)?
Shooting Easton Lightspeed 500's.

To, what kind of string silencers are you using? I have found that I can trim my cat whiskers or wool silencers and get quite a bit of spine change. Go slow, maybe 1/8" on each one at a time.

Let me know if it helps you.


Allen

sanding the shaft or leaving it longer is about all.

Do you have the brass inserts installed?

Use a thinner side plate (move the arrow closer to center) if that's doable. 1/32" is a lot....O.L.

What OL said.  I understand a higher brace height can be a little more forgiving of a stiff arrow as well.  Are you shooting dacron?  A no-stretch string will weaken your arrows as will longer shafts...but they are probably already cut....

I'm shooting an endless-loop D-97 string. Wool silencers can't be trimmed much.  Sideplate is velcro with a dime-sized piece of foam weatherstripping behind it - maybe I'll take out the foam piece and see if that helps.
Shafts are from another bow I used to shoot - they're already cut and as hard as I try, I can't get 'em to grow any longer...feed and water 'em every day.  They're still 31-3/4" long.
If removing the foam under the velcro doesn't work, I'll just add some heavier points - I was just hoping to match my broadhead weight (100 gr).

Three ways to weaken spine on a carbon arrow -

1) Increase tip weight
2) Increase arrow length
3) Decrease nock weight

I don't know if Easton inserts are tapped all the way through like CX and GT inserts, but if they are they'll be standard 8/32".

If I remember correctly the Lightspeeds are .246 ID, so the GT adder weights would work - but be sure to check the specs on Easton's site.  The weights just screw in behind the the broadhead with a long Allen wrench.  They come in 5,10,20,50gr.  On my target arrows I've added over 180gr behind the inserts, so they will work, and work well.

Depending on how far you need to go, though, new arrows or at least arrows that are longer from the start may be in order.

I'd get some heavier Broad heads! The bigger the better