Torsional rigidity and limb lengh

[Beardy]

I've now cranked my current limbs up to the max, so will soon be looking for some new ones, and Borders are at the top of myh list.

But a few questions for you before I make the trek oop north.

My current set up is
Winact riser at 25"
Everest Pros - long @ 34lb
Draw length is 30.5""
which gives me about 43lb on my fingers full wound in.

I'd like top go up a couple of pounds on my fingers so wound out I suspect I'll need something like 38lb limbs (on a 25" riser)

A longer riser (Bernelli 27") would mean that medium lims could be used. At this poundage would I gain anything in torsional rigidity?

Are long limbs (ie 70" bow on 25" riser) actually any less torsionally stable in real terms?

How about going the other way, would extra long limbs on a 23" riser give me better cast and less stacking? Would the reduced torsional stablity be noticed?

As to which limbs? Well that will depend on the budget, and she hasn't told me how much I can spend yet

Ta
Paul

[BorderBows]

This is a pig of a question in all honesty!
Firstly. Lets take vertical nocking point stability. The easier it is to push and pull your np vertically in line with the string the worse your arrow flight will get. This stability comes from the geometry of the bow. so here goes...
Lets take a triangle. A very stable shape. which you get from straight limbs comeing from the riser to the first contact point on the limb. Take you limbs fully wound out. This is where the limb butt is most inline with the limb. this gives the best triangle. Wind your limbs in and you get the limb butts in line with the riser, meaning the flexible part of the limb is now in a arc, this raduis, breaks the triangle and allows the np to move up and down more. This is never best. we recommend that you should only use the first half of the poundage adjustment!

For the same length bow, The longer the limb the less radius you get in your limbs for any given prelaod. for example, if you had 3" of limb, then the radia on that to achive BH would be rotten giving you more of a parrallelagram. if you had no riser then it would be a straight'ish line to the string giveing a better traiangle.
So there is a compromise to be had.

Next one. The further appart you get your laminates in cross section the more stable the limb becomes. The longer the limb the thicker the limb needs to be to gain the same poundage, this helps to counter the longer limb...

We would recomend, that you get the poundage you want on your fingers at your draw length. You shouldnt have to guess what you will get at 30.5" just because its easy to measure everything at 28"
For example, a set of 68" (meduims) Hex5 are 1.5 lbs less at 30" for the same at 28", and the TXG is 1lb less at 31" than the Inno. So not compairable.

This draw weight issue as well as a few other design obersvations being made are that to get the best of the hex5, you should be looking at half a bow length shorter. for example, the 29" draw length puts you on the cusp of 68"-70", we would say, most deffinatly go for the 68" due to the smoothness of draw that the DFC of the hex5 gives. This means that we would recomend the 70" limbs on a 25" riser to out past a 31.5" compaired to recomending the 72" TXG.

These three areas all influence the "correct" bow length (riser and limbs) to give you best overall performance, stability, speed and smoothness...