What kind of pole is strongest?

[Stuart Murphy]

Granted design, stitching, tear strength, probably more significantly than tear… tensile strength, zipper strength etc. play a role in how robust a tent is to forces that may be exerted upon it (including wind and snow as well as abrasion etc))it would appear that often the weakest link are poles.

So, which are strongest? Let the following questions guide discussion… answer any or all questions if you know.I'm interested in strong poles, with weight not such an issue.

1. Anyone had experience with Nemo's airbeams – they claim they are stiffer than standard poles (yet only market the air beam tents as 3 season, perhaps because the inflation process involves a foot pump which they warn may be difficult to use in soft deep snow). Seems a bit odd — if they basically unbreakable (read pop back up if flattened) and stiffer than normal…

2. Anyone have a preference for Easton 7075 vs 7001 series aluminium (or indeed the better quality composite material poles from the likes of http://www.fliegfix.com/)Carbon fibre is even used in full on mountain bike frames these days and manufacturers/designers are still improving such materials and the way they are used.

3. Why don't omanufacturers specify larger diameter poles? For a small weight penalty you get a vastly stiffer structure (there is a point of diminishing returns where the wall thickness becomes too small compared with the diameter and the pole therefore prone to denting). 11 or 12mm poles should be definitely stronger than standard ones without such risks I would have thought?

4. Does anyone have a sense of the strength imparted by large diameter poles (see 3) or by "double-poling"? I can imagine double-poling may result in 2x static (snow) loading capacity but only a marginal increase in the ability to resist wind before either pole breakage or tent flattening to the ground.

5. Do you think manufacturers specify poles as the weakest link in their tents for cost saving measures or to sacrifice the pole before the entire tent or seams shred?

6. On a related note, does anyone know the wind speed figures for the latest wind machine tent tests by Outdoor magazin (August edition I think). I would subscribe to the mag but I dpo not speak German :(

7. Would BPL be prepared to do some research in this (pole) arena? (+ can we all chip in for a wind machine lol)

Cheers
Stuart

[Kevin @ Seek Outside]

No idea why poles are perhaps not stronger. I've done a lot of experimenting with wind and snow loads and center pole tents.

The stiffer aluminum poles 6061, 7075 break before much deflection, softer aluminum poles bend more and can sort of be bent back, but in reality are never the same strength as before. The stiffer aluminum poles, are often ruined as well, due to not fitting right.

Doubling a pole, does increase strength. In the case of mids or tipis you can duct tape them together to get a pretty stable pole. Duct tape is pretty strong at holding things, in fact myth busters hoisted a car with duct tape. The problem is initial adjustment is a PITA.

Most poles, in mid / tipi style structures see a lot more stress in the center, meaning a pole could be smaller / weaker at ends.

With Carbon fiber, getting about 4x the strength on an 8 ft pole is about 6 ounce weight penalty (50%). My guess is aluminum would be 12 ounces penalty.

Carbon fiber usually breaks just one section, near the center if all poles are equal, or of center to the weakest section if they are not. This has some advantages, if you have an extra section, the whole pole is not compromised as many aluminum poles are. So while the aluminum will still operate, sometimes, depending on how it failed, it's pretty much compromised. CF , replace a section and you are fine. In fact, in some cases, a section can just be duct taped and made functional.

I've tried making weak spots or protection measures in a pole to absorb stress. More problem that it was worth, but perhaps some really clever person could figure a system.

[Manfred]

Hi Stuart,

>>>On a related note, does anyone know the wind speed figures for the latest wind machine tent tests by Outdoor magazin (August edition I think). I would subscribe to the mag but I dpo not speak German :(

I took a brief look and found the following information. They used a 500 hp wind machine that generated wind speeds of up to 150 km/h (93 mph). For any tent to be rated as "very good" it had to withstand 100 km/h (62mph). For a "good" rating the tent needed to withstand 70 km/h (44 mph)

I hope that helps,

Manfred

[Dale Wambaugh]

"Why don't manufacturers specify larger diameter poles?"

Cost, weight, availability, convention, and mediocrity– the same things that plague designs of any kind.

[Paul McLaughlin]

One reason manufacturers do not specify larger diameter poles is that the added stiffness means that they may require prebending to achieve the curvatures needed by the design in question. Stephenson uses a much larger diameter pole on their tents, and it intended to be much more rigid and comes bent to shape. This means it is a much more expensive pole to manufacture, and also means it is more complex to repair – if you damage a section you need to replace it with the precisely matching section of pole, since the curve is elliptical and thus the bends vary from one section to the other.
So while added stiffness results in a pole that performs better in many ways, it is harder to make. Not only costing more to manufacture but requiring more careful engineering.
I think that poles that are intentionally flexible are going to be the weakest link in the tent regardless of how much is spent on them. At some point they will flex too far, and either break or be bent so far that they get kinked. I don't see how you can avoid that if you require flexibility. Not that tent manufacturers are not trying to keep both costs and weight as low as they can, and pushing close to the lower limits of strength as a consequence: I just don't think that the poles are intentionally the weak link.
If you intend the poles to be rigid or at least very stiff, then you can make them as rigid as you choose to or can afford to (weight-wise or dollar-wise), and then you can reach the point where other aspects of the tent are weaker than the poles. Carbon fiber bicycle frames are intended to be stiff – some folks don't like them because they find them too stiff. From what little I know of carbon fiber composites, stiffness is what they do best, and making a flexible carbon fiber composite is far more complex.
As for double-poling, I would expect double the strength not just in snow loading scenarios but in wind loading as well. Not as weight efficient as a larger diameter pole but you avoid the stiffness problem, plus you have a safety margin since if one pole is damaged somehow you can still go single. Hilleberg recommends double-poling for extreme conditions.

[Antti Peltola]

"Stephenson uses a much larger diameter pole on their tents, and it intended to be much more rigid and comes bent to shape. This means it is a much more expensive pole to manufacture, and also means it is more complex to repair – if you damage a section you need to replace it with the precisely matching section of pole, since the curve is elliptical and thus the bends vary from one section to the other."

Simplicity and price is not the whole reason why some manufacturers like Hilleberg use the straight poles that need bending when you pitch the tent. In winter conditions, straight poles can be taped to single piece except for middle, and then be left halfway into the tent when in use. When packing the tent, you spilt the poles, then roll the tent around them. This makes packing and pitching the tent much faster, and is quite standard practice in cold conditions.

If my explanation was not clear, please check this pic:
http://4.bp.blogspot.com/-r7Zz3vRCzQU/TZbqZz53KCI/AAAAAAAAAY4/JxlhxiucMDg/s1600/IMG_2373.jpg

That red roll on top of the sled is a tent with the poles halfway on their sleeves.

[Stuart Murphy]

@ Paul

Re pushing weight boundaries. Yeah, i think things may have generally swung too far towards lightest weight possible compromising durability, strength etc eg. over the last few years 70d, 40, 30,… and now even 15d now for some flysheets. All things being equal that can't be as strong and long lived a tent (but materials strength/weight ratio of fabrics have improved… still,it seems that for non-expedition tents the marketing / design aim for lightest possible (even compromising living comfort)

Re carbon fibre stiffnes: Bike manufacturers are learning more and more how to effectively engineer compliance (at least if their marketing hype is to be believed). High end carbon fibre frames will often be touted as vertically compliant (for comfort) and laterally stiff. This is achieved becuase they have great control of tubing thicknesses (each vertical cross section can be narrowo than horizontal to encourage flex in one direction), and the direction they lay / align the carbon fibre sheets.Carbon is also supposed to be good at absorvbing some road vibration fequencies (though not quote to the same degree as a well designed quality steel frame – on the other hand carbon frames are a LOT lighter than comparabe steel frames)

Hmmm where's Roger Caffin… surely BPL need a wind machine (i.e. the ability to destroy tents in front of a camera for the scientific benefit of memebers??)

There are just too many unknowns with design, materials etc. We need some actual field tests. I'll donate a tent to be destroyed for the test data database.

[Rog Tallbloke]

I've had good use out of 2oz carbon fibre golf club shafts around 45" long. They get double use as walking poles. Good for supporting the centre of lightly poled dome tents in strong winds too.

[Stuart Murphy]

Please discuss pros cons of 2x 8mm poles vs single 16mm pole

As above but for single 13 mm pole. I would imagine a single 13 mm pole is stronger than sx8mm ones if you don't dent it?

What about tensile strenght… what does it mean for a tent pole – compare the largest and second largest diameter pole specs here (96000 psi vs 83 000 psi — what's it mean??):

http://polesforyou.com/tube_info.htm

Thanks for any advice.

Stuart

[drowning in spam]

A 13 mm pole is vastly stiffer. It takes some effort for me to bend them. Before I got my tent I had thoughts of retrofitting my tent to use 17 mm poles, but I'd probably have trouble bending them into place and get nasty bruises if I let the pole slip.

[Stephen Barber]

Paul says:
"From what little I know of carbon fiber composites, stiffness is what they do best, and making a flexible carbon fiber composite is far more complex."

A large percentage of fishing rods these days are made of carbon fiber or carbon fiber composites. They are quite flexible. It all depends on how the tube is made/engineered. The rod/tube can be as flexible or stiff as you want.

[Paul McLaughlin]

Yes, I'm well aware of that. The point I was trying to make, but I guess wasn't clear enough on, is that the more complex layups required for a more flexible pole means more expensive. I probably should have said "more complex and thus more expensive".

[Roger Caffin]

> Anyone have a preference for Easton 7075 vs 7001 series aluminium
The 7001 tubing is not as strong as 7075 T9, but it is not as brittle either. The 7186 tubing which made a brief appearance in the Easton stable was even more brittle. Trust me on that – I know!

> larger diameter poles? For a small weight penalty you get a vastly stiffer
> structure (there is a point of diminishing returns where the wall thickness
> becomes too small compared with the diameter and the pole therefore prone to denting).
You may find that Easton and DAC and others think the current wall thickness is about as thin as they dare go before the product returns start to mount up. Some customers have an unbelievable ability to damage poles. You might say they are experts at it…

Cheers

[Roger Caffin]

> One reason manufacturers do not specify larger diameter poles is that the added
> stiffness means that they may require prebending to achieve the curvatures needed
> by the design in question. Stephenson uses a much larger diameter pole on their
> tents, and it intended to be much more rigid and comes bent to shape. This means it
> is a much more expensive pole to manufacture, and also means it is more complex to
> repair – if you damage a section you need to replace it with the precisely matching
> section of pole, since the curve is elliptical and thus the bends vary from one
> section to the other.

I have to disagree with some of this. Putting a controlled curve into one of these poles is not hard. I can bend an Easton 7075 pole to a radius of about 10 inches. That may sound unbelievable, but I have done it. It's quite easy in fact.

Shops routinely replace pole sections for customers. If the pole needs to be prebent, and they do for most tunnel tents, then the shop assistant puts a rough approximation of the required bend in by running the pole over the edge of a wooden table. Yep, I've seen them do that. (Doing it that way does require a bit of practice though.) Precise matching of curvature … you have got to be kidding!

Cheers

[Roger Caffin]

> Hmmm where's Roger Caffin… surely BPL need a wind machine (i.e. the ability to
> destroy tents in front of a camera for the scientific benefit of memebers??)
At the date of posting (2/Sep) I think I was in Oberstdorf in Austria, at the end of seven weeks walking on the Via Alpina in the Alps. :-)

Cheers

[Joe Clement]

Not fair Roger. Not fair at all. And here we are, finishing the hottest summer ever measured.

[Diplomatic Mike]

Here in Scotland, and probably the rest of the UK, we have just had one of the wettest and coolest summers for decades! :)

[Kevin @ Seek Outside]

A lot has to do with if you are talking strait or curved pole. For a strait pole it's pretty simple, a small increase in diameter will double the ability of the pole to take downward stress. The weight penalty with CF is relatively small. The smaller walls are more troublesome. I think, just from observation there are some other factors at play as well, such as the use of ferrels. When under high wind loads, poles often will move, creating an area where the poles are not completely together and only part of the ferrel is keeping them together, and although this may be for only a short period of time, it is often where the pole will break. It seems a more solid connection such as a pin would prevent this. Just my observation

[Rick Dreher]

You wouldn't have to have ein Windmaschine, you could put a tent platform atop a car and go driving. You might need das Autobahn for the really high-speed tests, though. :-)

One common large-diameter pole application is teepee shelters. Every one I've had or used comes with at least a half-inch diameter pole. Clearly, their task differs significantly from that of a flexible tent frame though.

Cheers,

Rick

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