As has been pointed out in previous posts I did a comparison between two identical controller2 bars and discovered the lines on the
2 season bar about to be about 450 mm shorter than the new bar. The lines are always washed and no sand or salt is apparent between the weave as has been suggested as a possible cause of shrinkage. Ruling this out I can only guess that UV and the harsh conditions lines are exposed to is the causal factor.
I suppose if all lines (front and back) were shrinking the same amount and stayed the same length or were calibrated to be the same length then there should be no real difference in the performance
You measured them before use for 2 seasons use as well to see they were the same to begin with? I'm not disagreeing with your theory, but your tests are lacking a bit of control.
that is a pretty massive difference for only one season....which leads me to believe the newest generation and the second could not have been the same size to begin with. I would think that the lines would shrink unevenly, different favorite rotations and loops, jumping more favorably to one side etc. But the shrinkage would have been limited to 100 mm more or less. How many days did you put on the first bar? Really curious about this one.
No idea really ... but I have experience with a different shortening line. I have BWS Noise kites, and there's a line on bridle between front and rear lines that pulls through a ring. This dyneema line will shrink by 10% of its length over time. To me, seems counter intuitive...lines should stretch under pressure, no? But have now seen it on multiple kites and with multiple new lines...for sure it shrinks. In that example, I think it is something to do with the friction in that ring it goes through...generates heat or something?
Anyways, "shrinkage is real". We know all about that, kiting in Canada in winter. 
I've seen posts like these here before, and particularly publicised by a well know foil kite brand. I'm not convinced its real, or that it occurs to such a degree that it warrants our attention as kiters. My own experience from kiting for 23years, and in the early days making every line set we sold, by hand, lines stretch slightly over time, not shrink.
Some interesting links for those that care to read and know about these things.
www.samsonrope.com/?aspxerrorpath=/Pages/DemystifyingElongationandCreep.aspx
www.cruisingclub.org/pdfs/sas_lifelines.pdf
www.bethandevans.com/load.htm
Check the UV damage charts, 50% line strength loss after 5 years (of constant UV exposure? I think its days left in the elements), but there is significant strength loss even after a couple of years. Definitely store lines out of the sun and was in fresh water after use.
I can't, and never have found any scientific tests that prove the dyneema/spectra lines shrink over time, in use, other than on the brand's website mentioned above?
Willing to learn though if someone can point to some proper scientific testing?
... I agree with original poster, lines shrink and I have no real explanation of why except the theory that when lines are constructed, the weave is kind of loose relative to the final product as we know it and by working them, they just go back to the pre-stretched state.
The lines are stretched, made nice and tight with some manufactures putting some coating on them then sewn to the work of art we see before us. But over time by loading and unloading them ie flying the kite, the coating or what ever the stuff is wears off and they go back to the pre-manufactured state purely by just using them. I worked out roughly 2 percent or so, and in kite trimming terms is a lot. The more work the lines get, the more they shrink, which is the reason the front lines seem to go quicker than the steering.
I wanted to find out for myself so I measured all my bars one day (with tape measure) and noticed a direct correlation of shrinkage to age of use.
My control was a new un-used bar, then differing ages of use with 1 week, 1 month, 6 months, 12 months and 2 years.
Biggest difference I found was about 300 mm and they definitely got shorter the older the bar was,,,,,and of course the floppier the lines felt too.
Further to my experiments, I wondered if bridle lines did the same so I got the bridle measurements from manufacturer and then compared 2 kites (same model and size) with one kite that was 8 months old kite and the other 1 month old.
The older one (8 months) had all the inner components of the bridle roughly 1 to 2 cm shorter with the newer kite measuring exact to original measurements. The shorter bits were balanced from left to right side btw. Rough as guts pic:
Interesting the older kite flys fine, just not quite the same as the new one. You can only see it from a distance but the LE kind of flattens out a touch when under load, kind of like as if a 5th line is a touch short.
Anyway, just something I noticed!
Cheers,
Robbie 
Read a really interesting article on lines in kiteworld mag a few years back, based on braidtech eu , dyneema is chemically inert so unaffected by uv, they mentioned the volume of threads used was a big factor, from memory they spun 18 independant threads, the density of the thread is another factor, braidtech didn't mention shrinkage but gaurenteed minimal stretch, from a personal observation I'd say my old wipika lines have stood up better to the eye, my ozone bar 2010 is still going strong on original lines without any after kite tlc, and my flexifoil lines would have to be the most robust , personally I prefer lines that paragliding and land board brands use, not all lines have the same techniques , quality of material, quality control or skilled staff and equipment, so IMO the would be some difference in quality from brand to brand
Select to expand quotesir ROWDY said..
You measured them before use for 2 seasons use as well to see they were the same to begin with? I'm not disagreeing with your theory, but your tests are lacking a bit of control.
That's a pretty fair call.... I just assumed that the manufacturer would make all same model bar and lines sets identical give or take very minimal amounts.
Select to expand quotedafish said..
that is a pretty massive difference for only one season....which leads me to believe the newest generation and the second could not have been the same size to begin with. I would think that the lines would shrink unevenly, different favorite rotations and loops, jumping more favorably to one side etc. But the shrinkage would have been limited to 100 mm more or less. How many days did you put on the first bar? Really curious about this one.
The first bar must have done at least 200 sessions and maybe as much as 300 over 2 seasons The rear lines are uneven length and were adjusted when I calibrated the bar - about 50mm /1 knot difference. The chicken loop line also needed to be adjusted to accommodate correct front line calibration
Center lines are constantly under load so maintain their pre stretched lengths longer. Steering lines are mostly slack....
OP - measure your lines? If you're supposed to have 20m lines, it'll be easier to see what happened.
What is the water temp at your local spot? This could contribute to shrinking in length
Top brands line sets differ from batch to batch, its just a fact, not sure why, but they definitely differ. These differences could easily account for the differences in the bars in the OP's post. This is for woven/braided dyneema, not for sheathed lines, which I have seen and read about shrinkage (of the sheath, which is almost always not dyneema)
Front kite lines are not under "constant load", for a couple of blatantly obvious reasons;
1 - They are in your kite bag, in your car, etc
2 - when you ride, the pull is not constant at all, and varies substantially, like doing downwinders like I did today, the load is on and off constantly.
Again, lets all learn something, someone above said they could post 100's of pages and links on why dyneema shrinks, lets see it and learn?
You would think the yachting industry would have some information on dyneema shrinking, but I cannot find it.
All of the "tests" I've read about in this thread are not comparing apples to apples, sorry.
Who cares wether they shrink or stretch, just every 6 months check and correct them.
I just bought a single front line for my flysurfer lotus direct from FS , when i added it to the bar it was 3&1/2 almost 4inches shorter than all the other original lines on the 1 year old bar.
Lines are manufactured and stretched, then coated. The coating acts as a stabiliser and helps them stay at their stretched rate.
The issue becomes apparent if the coating de-stabilses. The easiest way to do this is with temperature.
North investigated this problem 2 years ago because of stretching issues and complaints within Australia. They found that about 83 degrees was the the crucial temp.
The issue that we have in Australia is temps in cars on a hot day can easily exceed this, in euroland 25 degs outside means a car temp of about 60 so line shrinkage is much less of an issue, but here 40 degs outside is about 85 in car, so lines destabilise and start reverting to their pre stretched rate.
Centre lines tend to stay stretched as they are under a constant load (while being flown)
So along with kids, animals and kites, don't leave your bar in a car on a hot day!
Select to expand quoteTerryMcTool said..
Top brands line sets differ from batch to batch, its just a fact, not sure why, but they definitely differ. These differences could easily account for the differences in the bars in the OP's post. This is for woven/braided dyneema, not for sheathed lines, which I have seen and read about shrinkage (of the sheath, which is almost always not dyneema)
Front kite lines are not under "constant load", for a couple of blatantly obvious reasons;
1 - They are in your kite bag, in your car, etc
2 - when you ride, the pull is not constant at all, and varies substantially, like doing downwinders like I did today, the load is on and off constantly.
Again, lets all learn something, someone above said they could post 100's of pages and links on why dyneema shrinks, lets see it and learn?
You would think the yachting industry would have some information on dyneema shrinking, but I cannot find it.
All of the "tests" I've read about in this thread are not comparing apples to apples, sorry.
Ok, not constantly then; center lines are loaded with a lot more weight, a lot more of the time, than the steering lines are. When the bar's in your bag, both centers and steering lines are slacked; it's a moot point. Centers will shrink less than steering because of load.
Mini-5th systems provide the most definitive answer so far, to me... without measuring lines.
If the centers were stretching past their original pre-stretched condition, then the Mini-5th would be getting "shorter", then returned to "normal" length when you trim front/rear lines. This isn't happening; once trimmed the Mini-5th is getting relatively longer and longer... the steering lines are shrinking faster, relative to the centers.
Why would shrinking lines matter in sailing? Paragliding is where you want to look, and there's lots of evidence there.
But I could be wrong. And I'd like to read more too. And my next new bar, I'm measuring my lines ;)
what an interesting thread.
ProductLinear Temperature Expansion Coefficient
- α -(10-6 m/(m K))*) (10-6 in/(in R))*)
Polyethylene (PE) 200 111
Polyethylene (PE) - High Molecular Weight 108 60
Polyethylene terephthalate (PET) 59 .433
Polyphenylene - glass fiber-reinforced 35 .820
Does it really matter? Just know you have to check them every so often and stretch them even again.
Here in the Pacific N.W. we all understand shrinkage. Cold water year round 
Oh line shrinkage Nevermind.
