Limb Length.

[2112]

I want too move up in limb length from 68 to 70 but dont want any loss in performance so the question is what weight 70" limbs would i need,(at presant i use medium G3,s 38lb @ 28 they weigh in @ about 44lb @ my draw length) to maintain the same sight marks.
many thanks.

[buzz lite beer]

I was told that the 2" increase in limb length equated to a 2lb+ weight loss for the same draw length, never actually tried it to prove it though! To get 44lb on your fingers from your set up your draw length must be some where near 32+ inches??? so 70" limbs should be the route to go.

[Wrexham Exile]

as above. i have 32" plus draw and use 70" limbs. i have 42lbs on the fingers using 32lb limbs.

the +2lbs rule seems to work ok but again havnt expereinced it in practice

[Timid Toad]

This is interesting, because I always believed that 34lbs@28 meant just that whatever length the limb. There is just less stack for the last few inches on longer limbs, so you are putting less effort in to get the same out. However, put 34lb limbs on a short riser, and then you'll go up 2lbs ish @28.

Him Indoors and I both have 34lb@28 limbs, same manufacturer, his are long (70") mine are medium (68"). When I draw his bow, there is no difference in the weight on the fingers to mine at my 29" draw length. He simply draws 3" further and gets 42lbs. He could do that on my limbs, but those last 3 inches would take an awful lot more effort to end up with exactly the same 42lbs. It may be that there is a difference, but we cannot measure it accurately enough to see it.

It would be good to have the definitive answer. Anyone?

[JohnK]

You will experience virtually no loss in performance moving to a 70in limb, especially if you get a model quicker than the G3.

Dave Kronengold (chief engineer at PSE) told me he ran some tests on bow length. He ran the tests using four different lengths of bow - all the same model and materials - all drawn to the same length and weight, and shot the same arrow through a chrono using a shooting machine. He found that there was only a 1 fps difference between each bow length (i.e. the 68in bow was 1fps faster than the 70in and slower than the 66in).

[robbo]

as above. i have 32" plus draw and use 70" limbs. i have 42lbs on the fingers using 32lb limbs.

is that within the limbs tolerances DMU?

i thought the acceptable increase was about 3% on top of the stated weight.

[Wrexham Exile]

got to remember that short limbs of the same poundage are also faster

as i said i use 32lb 70" limbs - but if i had 32lb 68" (cant though cos of my draw length) the bow would be much faster

[buzz lite beer]

So basically the (Shorter limbs+ Longer draw length = Stack), so your draw weight will increase considerably faster as the bow is drawn than those of longer length bow limbs. So in effect if longer limbs are used you reduce "stack" so won't get the same draw weight at your current draw length,

[Timid Toad]

Stack does not mean increase in weight on the fingers, it means more energy required to draw to that point. 32lbs@28" or 40lbs@32" is still just that.

Speed of the arrow will increase with shorter limbs, because they are more efficient, until stacking kicks in, where energy required (to draw the bow) exceeds what can be directed behind the arrow. If your limbs stack long before you get to your full draw length, performance will suffer because you will get tired quicker and unforced errors will creap in, and higher speed can give the feel of "twitchyness" that some describe. A lot of where limbs stack is down to individual manufacturers, and a little stack can give that magic liveliness and punchy feel. It is possible to put the maximum load of drawing limbs (per inch) in different points, some in the middle, some towards the end, its why limbs vary so much in shape. Thats why trying kit is so important.

Him Indoors' old 36lb@28" Nishizawa has terrific limbs - he could shoot 100yds, sight full out with arrows usually reserved for the compounders, but the draw force curve was shaped such that he was getting most of the load right at the end - just the last 4 inches or so, and it was killing him at the end of a day's shooting. He's changed to another manufacturer that gives him an easier ride for that last bit and he's doing much better - including increasing his drawlength a little because of better form. He also tried a 72" set, but found they didn't have that responsive feel, so he stuck with the 70"s.

By the sounds of your draw length, you do need 70" limbs or even 72", but the weight on your fingers will stay the same, with the same poundage at the same drawlength. However, you may lose a couple of fps, but it will be easier to get to your 32", and if you currently shoot a 68" bow, you might be stacking so much you could put an extra half inch on your draw length 'cos its so much easier, and make up what you have lost on speed. Plus you'll probably have a lot less errors through tiredness.

At the end of the day, its down to what works for you within some fixed guides and a few rules of thumb. Theory is one thing, but there are no standards, and every manufacturer has their preferred way as well. Beg or borrow other peoples' kit of varying lengths, and see what you can feel, both in the draw and through the rest of the shot. At the end of the day its what works for you that is important.

[Wrexham Exile]

Originally Posted by robbo

is that within the limbs tolerances DMU?

i thought the acceptable increase was about 3% on top of the stated weight.

sorry didnt see this post before.
how do you mean?