I once had 900ft of line attached to a couple of Flexifoil Super10 Stackers. The delay in turning was hilarious. 720ft was the sweet spot though. Ordinary mortals of course opt for a measly 20-25m on four line kites.

if you're talking about making handles... a foot of line on each end should be plenty.
obviously be certain that the breaking strength will be enough for what you want to do.
tom

Thanks for the replies - for what ever reason the body text of my original post didn't show up - which made the post look a bit rude - so trying again. :-)

I've been away from flying for a while (15 years) but looking to get back into it.

I'm going through my old kit and just wanted to check a couple of things.

Is there a standard length for the "leader"(?) lines coming from the handles and should they be the same length?

Does dyneema have a life span? I have a few sets of lines in my bag and as they're about 18 years old I thought it worth checking to see if they might be past their useful life.

I have also bought a new 4 line set. I need to check their length and just wondered what's an acceptable tolerance in length between the four of them?

The new lines are sleeved differently now - with a neatly stitched sleeve - which I'm not sure how I'd go about altering. When I used to fly I'd buy dyneema from my local (long gone) kite shop and sleeve/knot it myself.

Should new lines also need stretching before use?

there doesn't seem to be a standard leader length. some that i have are about a foot, some are around 15", one is definitely longer than that, but i haven't measured it.
your old lines should be good if they're not badly frayed. the new lines will likely be pre-stretched, and should not need any altering.
the new set should all be quite close to each other. if not, just adjust the knot distance on the handle leader line to match them up.
if i am wrong, i'll probably be corrected quite quickly here...
tom

Plingboot, as far as tolerance between each line length, you want to be real close. You can do a little bit of stretching if the lines aren't dang near even. Just a little bit of difference between the powers line set or the brake line set can send a 4 line kite drifting one way or the other or even worse, stall on you. My way of checking line lengths and stretching was to anchor one end of he lines to the ground with a kite stake, run them out and put a screwdriver through the loops on the other end you are holding. You can then pull on the appropriate line to make sure they are pretty close. As far as difference between power line lengths and brake line lengths, a little bit is ok as long as you have a way to make adjustments on the kite end or handle end to compensate. Brake lines should not be taught when launching the kite, you want a little slack back there.

As stated, 25m is standard for most kites, it's all play to pleasure after that.