How tight should tent guylines be?

Guylines should be taut enough that the flysheet does not flap, and no tighter — a rigid pitch tears where a slightly forgiving one flexes. The rest of the answer is about angle, order and what the fabric does when it gets wet.

What tension is for

A guyline does two jobs. It holds a panel out so that the flysheet stands clear of the inner tent, which is what stops condensation on the fly transferring to the inner. And it stops the panel drumming in wind, because flapping fabric is what abrades coatings and eventually splits a seam.

Both jobs are done at moderate tension. Winching a line until the fabric is hard concentrates load on the tie-out patch and the peg, and in a gust the whole structure has nowhere to go. A pitch with a little give absorbs that gust and comes back.

The usable test is visual: the panel should be smooth with no standing wrinkles, and pressing it with a finger should give a few centimetres of movement rather than none.

Angle and peg placement

The line should run roughly in the direction the seam or pole is pulling, so the load travels straight down the cord. A peg driven too close to the tent makes the angle steep, which converts the pull into an upward force on the peg — the reason lines pull out in wind is far more often geometry than peg length.

Place the peg so the line leaves the tent at a shallow angle, and drive the peg at roughly a right angle to that line, leaning away from the tent. The head of the peg should hold the cord low, near the ground, rather than letting it ride up the shaft.

Where the ground allows nothing, the anchor changes rather than the tension: a line around a rock, a log, or a stuff sack filled with sand and buried is doing the same job the peg was.

The order in which you tension

Pitch and peg the corners first, so the floor or fly is square and the poles are loaded evenly. Then take the main guylines — the ones on the ends or on the pole crowns — before the secondary mid-panel lines. Tensioning a mid-panel line on a tent whose corners are not yet square pulls the whole shape sideways.

Work opposite pairs rather than going round in a circle. Each line you tighten slackens the one facing it, so a pass round the tent leaves the last line doing all the work.

What the fabric does when it rains

This is the part that catches people out, and it is a material property rather than a mistake.

Siliconised nylon absorbs water and stretches when wet. A pitch that was taut at dusk will be visibly slack after a few hours of rain, and it needs retensioning. Siliconised polyester barely stretches, which is why some makers use it despite the weight penalty for a given denier. Dyneema composite neither stretches nor absorbs water.

Read the fabric on the specification sheet before the trip, not at two in the morning. If it is nylon, set the line-locks somewhere you can reach from inside or from the porch, and expect one retension.

Cord and hardware

Guylines are consumable, and the ones supplied with a tent are often the first thing worth replacing. A cord with a reflective tracer woven into the sheath is far less likely to be walked into at night. A line-lock or tensioner adjusts without untying, which matters in the dark and in gloves.

Check the tie-out points on the fly for reinforcement while you are there. Those patches are where the tension you apply ends up, and a line tightened harder than the patch was designed for is a repair waiting to happen.