Marvelous!!! On behalf of me and all our students trying to apply ziplines without trees to impoverished communities in the highlands of Columbia we thank you!

Thank you Ryan that was an outstanding explanation I was planning a similar installation. I was considering 6 5/8 “ galvanized pipe. So glad I saw this post since the cost of building materials are through the roof!

This was Awesome, thank you for this excellent Video, I have a handyman side gig and need to build a Zipline for a customer. I actually have a mechanical engineering degree as well so was able to follow along with your formulas.

You are a legend, thank you so much Ryan! (repeat on blackboard 100 times)

Thank you for this video! Thanks for sharing your knowledge! Very helpful!

Thank you. Very thorough. Building mine soon!

Thank you Ryan, you answered all doubts..Dan

I have a 500ft zipline in my backyard and we just used a string as a rough estimate of the height we needed. For some 250lb riders, they will bottom out in one spot, so we use a shorter leash for them to fix that issue and with really small kids we use two leashes so they can reach the platform at the end.

You just made my head explode.🤯

Thanks for the video, really enjoyed it. I'm attempting to put a zip line in my garden for my kids to play with and plan to use 12x2 timber laminated together like you did. Was the 4ft depth of the end points based on a calculation? Im digging by hand in hard stony soil and am wondering if 3ft will be deep enough? What do you think?

Hi Ryan, Great info and great video. Have seen many people use your guidance videos. Would steel RSJ type beams work? Thank you.

When I'm just interested on how to build a zipline post by myself but I ended up learning physics and all. Win:win situation

Hi, thanks so for much for the video, currently helping someone build one. Three quick questions: 1. How much elevational difference is needed (or ideal?) between the two 'trees'? 2. Depending on your answer to #1, if someone is on flatter ground might they need to allow for less sag so that momentum is not lost? 3. Lastly, for the dimensional lumber, do the proportions matter at all or strictly the cross-sectional area? Is a 6x6 post as good as a 2x12 for this? I am working with one natural tree at the high end & one man-made 'tree' at the low end. So if the connection point on the actual tree is at 3.4m I am trying to figure out what height is ideal for the low end with about 600mm of actual elevational difference in the ground. Thanks!

I have a slackline that has multiple hanging obstacles from it. It requires a 12" tree which I do not have. Could I use these same size posts to connect it? It states it needs to hold 2500 lbs.

The joy of math and the comfort of science! - excellent explanation. Do you have a checklist of items &links to purchase.

Did you check the margin of strength on the cable (and connections)? At what rider weight does the cable start to yield? If it yields, is it still usable afterwards if you tighten it? Do you know if cable work-harden? I am considering a zipline for my grandkids, and appreciate your engineering. I am a retired aerospace engineer, and make similar videos on various projects. The more math, the fewer the views, unfortunately.

This video was really insightful, thank you for posting it and especially breaking down the math. This may be a dumb question, but would the same calculations work if the numbers were different values? For example, if I wanted one that was longer and higher, I could use my numbers in place of the ones you plugged in and still get an accurate amount of slack and tension?

Very useful video - thanks Ryan. Like Luke below I also based my calculations on a 200lb rider over a 120' distance and the deflection was coming out at over 2", which is higher than I'd like. I don't have the space to use a guy anchor so I figured I would use two 2x12 beams in series in line with the run, with 12" to 18" between them and bolt the beams together at the top and middle with a couple of pieces of 2x12 - think of it as something like this |=|. Each beam will be set in it's own (4' 5" deep) concreted hole so I'm hoping that will provide more than enough strength/rigidity.

How high could I make these anchors? Would I be able to use 20' lengths for a 90' span?

Amazing video! Thanks for the calculations! I was planning on using the clubhouse I was building until I determine how much lateral force would be acting on my wall. One point of clarification on your calculations. 2x12 is nominally 1.5 x 11.25, not 11.5. It jumps down between 2x8 and 2x10's 1.5 x 7.5 and 1.5 x 9.25. Weird, huh? Do you think it would be possibly to anchor the wall back to a tree, if the wall were in the same line as the zip line on the other side of the wall?

excellent, thank you!

I noticed that the beam bend equation you used assumes the load on the beam is at a 90 degree angle. I suppose that not completely accurate since the cable tension would NOT be exerting force on the beam at a 90degree angle. But I suppose assuming the force is exerted at 90degrees would be the worse case scenario. Is that what you were thinking?

I'm am trying to model our proposed solution using Blender 3D physics simulations and animations -- great to see you using Sketchup!

As I watch your calculations (with gratitude and fascination, trying to relearn the math!) I realize that if the downward deflection is between 3 and 4 feet (37.5" to 48") our IBC tank anchored zipline system isn't going to be all that successful given that an IBC tank is only 3 feet tall and we would be putting the cable sling somewhere lower than that... Hmmm. A failure? Or can we increase the tension (since nobody will be riding on it but it will be used for transporting cacao pod baskets). Any ideas?

do you need to consider the weight of the cable in the force applied to the end points? 100ft of decent cable is pretty heavy.

can you please show /tell us how the rebar was used in the base hole? thanks

Any reason why 2x12x10s wouldnt work. If end height needs to be 78inches, with 3ft in ground that leaves enough out, no?

Really nice calcs, ¿did you check the estress on the cantilevered beam?

Hello Ryan, I am going to build the same set up in my back yard for a 75' run. I have no slope and was hoping to have the ending height at 8' and starting point at 12' to 11'6" depending on the speed. Using 16' post on high side and 12' on low side. I ran through all the calculations with similar assumptions for a 8' at the end and 12' height at the start. Drop of 4' and the same stats for the wood. I used a 160lb as the rider for me, kids only 50 - 80lbs. T = 754lbs of force, degrees are 6.1. I calculated deflection at 1.35" for the 12' and .4" for the 8' side with 2.3" of cable stretch. Total deflection of 1.75", I am not sure how to feel about this, and if this is too much for the posts. . Solving for B^2 I got 42.74". This seems like the it within parameters, would you recommend a guy anchor on either side for additional support? I was thinking about adding one to at least the 12' side, do you think it is needed? I can always add after if i get more deflection than I calculated. Would you be satisfied with these result doing the same set up you did, but just a higher starting point? With 3 2x12's on the high side I get Total deflection of .9" + .4" = 1.3", would you think the post can sustain this amount? Thanks for the formulas and example to help calculate. .

Is this missing in your calculations? -- cable weight -- shouldn't the weight of steel cable itself be added to load mg? my cable weighs as much as my 100 lb son so would that not double the tension required to hold son AND cable? Thanks, (currently building 450 footer)

Hi Ryan, I am an engineer myself but haven't dabbled in structural work since my University days so have just been refreshing myself to help with design of a post to fix a zipline and/or slackline to and stumbled across your video. The product manual I have for the slackline recommends designing the post to handle a load of 11.5kN (appears to be the rated capacity of the line). Just wondering if you gave any consideration to the force on the post generated from setting the zipline to the required tension for use, prior to loading from users. This is probably more applicable to the slackline installation which comes with a ratcheting strap and needs to be set quite taught for use. Thanks

Any particular PSI recommended for the concrete?

Great explanation! Did you look at using alternate materials such as steel or aluminum posts with or without guy wires?

Using telephone poles. 5% decline in terrain with 100’ run. Thought larger pole should go at top. Does it matter? 10” diameter pole vs 12” diameter. Concrete will be poured 4’ deep holes 3’ W x 6’ L

Fair enough Ryan. I was rounding up from 7.5" to 8". I know the website I showed you recommends 12" and 8"...I am just trying to figure out if the 12" for the main pole is overkill, but I understand that your patience is exhausted.

Hi. You assumed at 1:40 that the rider is gonna drop 4ft over a 90ft run. Why did you assume 4ft? Is that from the sloap of your yard that is 4ft and bems at 8' tall?

Thanks for the engineering. It is refreshing to see this applied rather than people blindly hooking stuff up and saying "good enough". The only calculation question I had is if the mass of the cable needed to be factored as part of the weight? I have a decent 40cm yellow birch tree at the top, and nothing at the bottom 70m away and 12m lower. I was wondering if you had considered running an additional cable down at about a 45-60 degree angle to a ground anchor in order to minimize load on the post/tree? From an engineering standpoint, this seems like it may be better with significantly higher loads from the longer run.

Hi Ryan, I really appreciate your video. I have one question. You solved for tension this way 2*T*sin(theta) = 100 lbs (mass?). My question is this. Isn't tension a force? Shouldn't the equation be be 2*T*sin(theta) = 32.17405 ft/s^2 *100 lbs and then solve for T? If I'm right the horizontal load on the post is 1433.1795 lbf. I'm not trying to be a smarty pants, I'm just trying to make sure I understand. Thanks for the video its well done.

The one thing that wasn't clear was that because of slop in your line your zip line was 4 feet lower at one point?

I have a customer who wants me to install a zip line inside their house from second floor to first floor I don’t think it’s possible any suggestions on how to do it so nobody get hurt

Two 2x12’s are better than one 4x12?

Hey Ryan thank you for the video, my brother in law did exactly what you suggested, I just don't like the look of 2 2x12's coming out of ground, I was thinking 2 4x6's bolted together. Please tell me your thoughts

Hi Ryan. Did you do any calculation on the depth that you buried the post and diameter of the hole? I found an equation, "Eq. (7)", in the following article, which results in about 19,000 N to push over your post. Compared to the 2,500 N generated by the 100 lb child, this seems really safe. Maybe, a smaller hole would work. A 12 inch diameter hole results in 8,500 N to push over. I am considering using a steel pole and smaller hole. Article: digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1206&context=usarmyresearch Google sheet with my calculation: docs.google.com/spreadsheets/d/1xNHCyY33ueuB8tualJnHPk1vvi34AXowaCzkakxISpo/edit?usp=sharing

Thanks for posting this Ryan. I was going through the calculations myself, and I used a 200 lbs rider (if I'm going to build it, I want to be able to use it myself too :) and I found that for two 2 x 12 planks, the shear stress was 1305 psi engineersedge.com/beam_bending/calculators_protected/beam_deflection_9.htm. The shear strength for pines is between 885-1500 psi www.engineeringtoolbox.com/timber-mechanical-properties-d_1789.html, so I wasn't comfortable with that. I found a lumber yard that sells locus logs (don't have to pay for having it finished :) If it works well, I'll post again. I see that you had a good 4 year run with your design - that's cool.

I'm like.. 210# (me) T= mid 1100's dang.. "..were going to need a bigger boat".

What the fuuu??