All right, I know this topic has been discussed before but I was recently making some line tuning and decided to push my experiments further and measure a couple of old lines vs brand new lines, this time with a few different manufacturers.
2 years ago I just couldn't be convinced that lines were shrinking instead of stretching, which really goes against common sense and popular belief.
All lines pictured were attached to a fixed point and put under tension. Even 5M line extensions have shown some shrinking (a few cm), but in excess of 30cm of shrinking for some 2 season old back lines! As you can see, front lines shrink as well, but just at a slower rate since they are always under load (still 20cm in some cases!)
It seems the combination of salt water, sand and hot weather contributes to shrinking. Since lines are always pre-stretched in the factory, it makes sense they can only shrink.
It would be nice to have some kite lines manufacturers weigh in on this topic?
Anyways, I'll let let the picture do the talking:
Christian
Yes they do shrink. Flysurfer has been publishing this for year.
Its counter intuitive. But think about it. The lines start off compact and thin. Then they get rubbed and worn and become thicker and fluffy.
That thick fluffiness has to come at the expense of length.
I remain unconvinced. From my own purely anecdotal experience
Heavier guys seem to have more trouble with line lengths.
Myself coming in at under 75g and owned many kites of different makes
Have never seen stretching or shrinking.
Select to expand quoteWanga F One said..
I remain unconvinced. From my own purely anecdotal experience
Heavier guys seem to have more trouble with line lengths.
Myself coming in at under 75g and owned many kites of different makes
Have never seen stretching or shrinking.
When i replaced my Core lines this summer, they had shrunk after 1 season. Not a lot but noticeable and i'm 52kgs heavier than you.
Maybe now you've finished replacing all your lines Christian, you can do some gardening 
Select to expand quoteWanga F One said..
I remain unconvinced. From my own purely anecdotal experience
Heavier guys seem to have more trouble with line lengths.
Myself coming in at under 75g and owned many kites of different makes
Have never seen stretching or shrinking.
because heavier guys centre lines will shrink less than their steering lines, whereas lighter guys will have all 4 lines shrink more evenly making it less noticeable
Select to expand quoteflyingcab said..Wanga F One said..
I remain unconvinced. From my own purely anecdotal experience
Heavier guys seem to have more trouble with line lengths.
Myself coming in at under 75g and owned many kites of different makes
Have never seen stretching or shrinking.
because heavier guys centre lines will shrink less than their steering lines, whereas lighter guys will have all 4 lines shrink more evenly making it less noticeable
Correct.
It must be said that there's a few different things you could be talking about here; 1. stretching on a day to day basis, or, 2. shrinking over considerable time.
Lines are not always "shrinking" as such but more likely a combination of extra fluff (as mentioned above) and also the fact the fine sand can get into the weave and make the line fatter, obviously decreasing line length over time.
That being said, if my rear lines are un-even (or a front) from session to session it is usually because one line has stretched while the other 3 have stayed the same, not because 3 have shrunk while one stays normal
. Over long periods though they will all get shorter.
What about the amount you wash your lines?
I dunk my lines in a bucket of fresh water after nearly every session and have never had any significant shrinkage, one set of lines is 3 years old.
Could washing the salt / sand out make the difference?
Select to expand quotenigelw2 said..
What about the amount you wash your lines?
I dunk my lines in a bucket of fresh water after nearly every session and have never had any significant shrinkage, one set of lines is 3 years old.
Could washing the salt / sand out make the difference?
Probably, I'm going to take a guess and say you are probably washing the salt and sand out of the weave and as such are stopping them getting shorter.
In the end though what's the problem? I mean if they all get like 20cm shorter over a few years I don't see how that's a issue.
Been using the same set of q powerline pros for the past 8 seasons....they haven't budged, they have an extremely tight weeve and have zero stretch ...may be why.?
My 11m 2013 Switchblade had been flying progressively poorly and our local shop suggested checking the lines after having watched it flying. Following the Cabrinha line tuning video, I found that the two front lines were uneven lengths and the back lines had shrunk an estimated 10 - 12 cms. It took about an hour of adjusting the knots to get them all the right lengths, but the kite was flying normally again the next session.
I take pretty good care of my kites and wash the bar and lines in fresh water after every session and I must say I had doubts about line shrinkage, but not any more. Seems counter intuitive given they are under tension, but they do shrink at varying rates.
You don't need to adjust any knots, just tie the shorter one to something solid and pull on it. You can usually stretch your lines back to equal by hand very easily.
I totally agree with Cbulota's findings. I rarely wash lines, if ever and find the same shrinkage across my foils and LEI's (yup, got a couple in the back of the garage somewhere). You'll notice you need more and more trim on to stop backstalling, this is more noticeable in underpowered conditions.
For those of you on Flysurfers, this is why the front lines are tied to the top of the trim strap with a figure 8 knot (under the neoprene cover). This enables you to progressively shorten the fronts to restore all to the same length, and gain the full depower range back. Simple fix really
What about dettol washing your lines?
www.seabreeze.com.au/forums/Kitesurfing/General/bad-to-wash-kite-lines-in-hot-water
hahaha that's awesome. I wouldn't have believed if for a second with out the pics.
shorter lines = a faster kite, and faster loops, am I right?
After 1 years solid use I found that my front lines were a bit shorter than my back which seems to be the opposite of what people are saying here, also as I can only really jump well on one side I find that after a couple good jumping sessions I have stretched one side and then need to stretch out the other side by securing all lines and tuning them appropriately, I was having constant issues with uneven lines but now as I am tuning them more regularly it is much more under control
Select to expand quoteMDSXR6T said..Wanga F One said..
I remain unconvinced. From my own purely anecdotal experience
Heavier guys seem to have more trouble with line lengths.
Myself coming in at under 75g and owned many kites of different makes
Have never seen stretching or shrinking.
When i replaced my Core lines this summer, they had shrunk after 1 season. Not a lot but noticeable and i'm 52kgs heavier than you.
Maybe now you've finished replacing all your lines Christian, you can do some gardening
Sticking with the forum rules, "no post containing a photo of kitelines on the ground shall be complete without at least some discussion on the health (or otherwise) of the lawn".... 
I somehow knew someone would say something about the garden. Better stick to the beach next times
If your garden looks too nice maybe you're not kiting enough
A little off topic but in the 4th photo from the top (the one showing the 2 core bars) what is that little bit of what looks like steel next to the depower line?
My knowledge of Core kites is not the best.
Oh and just me 2 cents while i'm here from my experience lines can shrink and they can stretch depending on what is happening to them.
My lines are made of thin 2mm stainless steel wire.. They don't stretch or shrink. It is the new future of Kitesurfing.
It doesn't really matter whether they shrink or stretch. They can change length and you do have to retrim them from time to time.
Even if they shrink it appears that the rear lines shrink more than the fronts. Every time I have re-trimmed the front lines have been longer than the backs.
I find it hard to believe that much shrinking is really going on. My brand new lines are very dense and stiff. My old lines are soft and floppy. Where has the space come from to make the lines floppy? If the lines have shrunk why aren't they more dense and stiffer?
Logically stretching lines makes no sense at all. You're riding around with about 80kg of weight hanging off them for hours on end and you're loading them up and popping and blasting around. Then you go home and put about 10kg of load on a line and expect it to stretch?
I used to stretch my paraglider lines each year, mainly because it is easy to do and you can see them give a little when you pull them.
I recently re-trimmed my glider and measured the lines with a laser measuring rig before and after stretching. Stretching made no difference at all.
After 250 hours use most lines were within 10mm of the designed length. The front centre lines were longer by 15-25mm. Paraglider lines are just under 8m long compared to 22m kite lines.
Well I have never measured my gear with laser beams or anything but after a good stretching/ tune up it seems to fly a lot straighter and that's good enough for me
Select to expand quoteGorgo said..
Logically stretching lines makes no sense at all. You're riding around with about 80kg of weight hanging off them for hours on end and you're loading them up and popping and blasting around. Then you go home and put about 10kg of load on a line and expect it to stretch?
Maybe it makes no sense, but I can tell you with 100% certainty that it makes a difference and that almost all pro riders do it when their back or front lines are off by a cm or so. Maybe it's something other than the line that stretches, but I'm pretty certain it's the line, you can stretch a lot of lines by a considerable amount if you try.
I've noticed that after a good session of boosting always on the port tack, that my right arm is longer than the left. Normally by about 2cm's.
But I haven't used a laser to verify this, so just take my word for it.
Select to expand quoteDamo said..
Oh and just me 2 cents while i'm here from my experience lines can shrink and they can stretch depending on what is happening to them.
Yes, and depends on how long they have been used...
This test is very good, but quite limited. I'm thinking this is case...
For example, after first session lines will shrink.. Material is new, and it's pre stretched so it goes in state where it was before stretching.
After lets say about 5-20 sessions lines will stop to shrink and easily start to stretch.. (almost perfect length)
After about 200 sessions lines will be bit longer than original..
After about 500 sessions lines will be quite bit longer...
At some point they will break and no one can convince me that after 500 session lines could be shorter that original...
