When setting up a tent and staking it out, what is the proper tension for the lines? I generally just make them arbitrarily tight, but have no idea how that would perform in high wind or other conditions.
There's no hard and fast rule for specific tensions that I know of, mainly because that will vary slightly depending on the conditions. As an average rule I tend to make them taught, but not to the point where they're pulling on the pegs.
There's a couple of scenarios where I tend to slacken them off a bit though:
Other guidelines are much more important though - things like having your pegs in at a slight angle away from the tent, making the lines nice and long and spreading them out well. I find those 3 things generally much more important than how tight the lines end up being.
When I was in the scouts a few years ago we used to use patrol tents with natural fibre guy ropes. We were always taught to slacken the guys off when it started to rain because the ropes shrink. Sure enough one patrol didn't do this and the 2" diameter ridge pole snapped leaving some very unhappy campers.
I realise that most tents these days don't use natural fibre guy ropes but I think it's still worth being aware of.