Rope break strength question... want to build a tire swing :)

[Muse]

Use nylon, won't rot, very durable. Strong. Get the nice thick stuff they use for anchor. You want some thickness so it feels good in your hands, it will not chafe your hands like other types of rope (feels nice and smooth), and the strength at that thickness is humongous. I was a physics major for 2+ years but I don't need physics to figure out this one.

pftt! Use steel cable and make a zip line.

Problem with steel is the moment a strand breaks you have potential to cut your hands. No way I'd use steel for a swing.

Atot...
The only place where making a rope swing is seen as a monumental engineering challenge.

eh

 

[ajf3]

I was planning on sheathing the rope in some rubber tubing where it wraps around the trees to protect both surfaces... I guess the girdling might be a problem, but I don't think these trees are going to grow much wider there for the span of time the swing would be up...

 

[Matthiasa]

Someone beat us to it.

Oh and since it hasn't been asked can we at least get pictures of the trees in question?

 

[ajf3]

Here you go... http://i.imgur.com/dkRQo.jpg

The diameter is around 13-15" at the bottom, probably 10-12" or so around 20' high, but I haven't laddered up to measure it yet.

 

[DrPizza]

but then there will be rotation at the point of connection to the trees...couldn't that cause abrasion/wear?

No. Look at a swing hanging from the branch of a tree (something that 90% of ATOTers probably have never seen) - the rope is wrapped around the tree & tied. Only if the rope is loosely wrapped around the branch will it rub back and forth. The fulcrum as at the knot, not the top of the branch. In the OP's case, the fulcrum would also be at the knot if he ties it fairly tight around the tree (probably two wraps around the tree & a doubled square knot would do.

Of course, the downside for the OP is that as the tree grows, the tree will grow around the rope, encapsulating it. But this will take quite a few years; he should be good for 2 or 3 years at least.