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P-pod for dry camping?

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MarkW View Drop Down
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Post Options Post Options   Quote MarkW Quote  Post ReplyReply Direct Link To This Post Topic: P-pod for dry camping?
    Posted: 06 Apr 2021 at 6:40pm
If a bolt has a tensile failure point of 2000 pounds, typically you do not see it used in applications where it would be subjected to 2000 pounds under normal working loads.  The working load would be a percentage of the failure point.  

Sure, but we really don't know if bolt strength ratings are a good analogy to vehicle tow ratings or not -- we can't just assume that's the case (and that's certainly not the way that manufacturers intend their tow or other weight ratings to be interpreted by customers).  

But the big problem with this discussion is a lack of real-world data.  What percentage of those towing bumper-hitch travel trailers ever experience uncontrolled sway that causes a crash?  For those that do, what were the characteristics of the TV, trailer, weight-and-balance, sway control, speed, winds, etc at the time of the accident?  Again, we just don't know.  There's no NTSB investigating every travel trailer crash as there is with aviation.   Maybe somebody has a good collection of TT crash data, but I haven't been able to find it online.  
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lostagain View Drop Down
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Post Options Post Options   Quote lostagain Quote  Post ReplyReply Direct Link To This Post Posted: 06 Apr 2021 at 7:09pm
The point is that it is not a good idea to exceed the working load, indeed, it's probably safer to stay a bit below it.  There is more that goes into the equation than simply a working load.  You also have to anticipate other factors that may affect the bolt's capacity, such as oxidation, metal fatigue, the climate where the bolt or other breakable thing is being used, it's age, etc. etc.  

You logic seems to be that if you don't know all the variables, then it's just fine to push the manufacturer's limits.  No, you don't know all the data, but more than likely the things you don't know are not things that will enhance safety.  Many people who drive trailers with marginal TV's are not always the best drivers and don't realize the limits of their skills or their vehicle.  Driver fatigue, wear and tear on the hitch and chasis, poorly balanced loads, poor brakes, bad electrical connections in the brake system, etc. etc. etc. are all things that can justify erring on the side of caution.

We don't have all the real world data, but we do have some pretty smart engineers on this board who have wisely cautioned us, based on their engineering experience, that it is good idea have an adequate margin of safety.  It's is unfortunate that NTSB doesn't offer a database that specifically addresses travel trailer towing accidents, but that does not mean we can use math and science to calculate the risks of towing.


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Post Options Post Options   Quote MarkW Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2021 at 7:03am
You logic seems to be that if you don't know all the variables, then it's just fine to push the manufacturer's limits.

And your logic (without any evidence that I'm aware of) is that manufacturers are lying and that safe tow loads are actually much lower than the published specs.  But why would they do that?  After all, few of their customers are engineers who understand the distinction.  Certainly for pickup trucks (where -- unlike crossovers and minivans) max towing capacities are a major marketing issue, they claim their trucks can tow up to xxxxx lbs! and not 75% of xxxx lbs (even in the fine print).  They'd face MAJOR lawsuits if they were misleading customers in this way.  

But when you look at the actual tests, it's pretty clear that this not what they're doing.  The SAE J2807 tow tests specifically include extreme conditions (towing the max rated load up a long steep 11 mile grade at 100 degrees and with the A/C on full blast):

To simulate some of the toughest conditions a truck and trailer combination will face, the J2807 “Highway Gradeability” tests take place on a well-known stretch of Arizona highway, the 11.4-mile-long Davis Dam Grade. If trucks are not tested on this specific stretch of steep road, they can be run in a simulation using a “climactic” wind tunnel. Ambient temperature plays a significant role in this test with a minimum temperature of 100 degrees required at the base of the grade. In addition to a hot climate outside the truck, the test requires the air conditioning system to be set at maximum cold, with outside air selected (not recirculating) and the fan running at full blower speed.

http://www.trucktrend.com/how-to/towing/1502-sae-j2807-tow-tests-the-standard

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lostagain View Drop Down
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Post Options Post Options   Quote lostagain Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2021 at 8:56am
No, Mark, you are engaging in sophistry misstating what I have said.  

I didn't say that if you don't know all the variables then it's ok to push the manufacturers' limits.  I said just the opposite.  There are many variables that we don't know that make it judicious to take the limits of the manufacturer seriously and not push them.  I suggested that many of those variables reduce the safe load capacity and that one should, as the engineers on this board have suggested, try to have a margin of safety below the manufacturers' limits.  

Your suggestion that the logical conclusion of my statements is that manufacturers are hiding the true load capacity and that it is really much lower, couldn't be more wrong.  Again, you are engaging in sophistry by misstating what I said.  I take the manufacturers' load limits seriously and unlike some, believe that they (and the government regulators and even lawyers), have my best interests in mind, though it may not be for the altruistic motivations I'd like.  My point is that we should accept those load limits and add to the margin of safety other considerations that effectively reduce load limits such as a driver's skill, reaction time, experience and so on, not to mention the condition of the vehicle, road conditions, etc., all of which mitigate in favor of a wider margin of safety.

OG and GlueGuy have both stated that we should have a wider margin of safety than less.  OG has been nice enough to have given us the math that supports his advice.  Both are engineers and I, as a lay person, am going to take their advice seriously and keep my towing loads below what Ford tells me is the limit.  
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Post Options Post Options   Quote MarkW Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2021 at 10:53am
I didn't say that if you don't know all the variables then it's ok to push the manufacturers' limits. 

I didn't suggest you said that.

I suggested that many of those variables reduce the safe load capacity and that one should, as the engineers on this board have suggested, try to have a margin of safety below the manufacturers' limits. 

But the manufacturer limits are not based on ordinary driving but rather on extreme conditions (towing the max weight up a steep grade for many miles, in 100 degree heat and running the A/C on the max setting).  I'll already be leaving a margin under the limits by never doing things like that.

My point is that we should accept those load limits

Agreed -- for insurance / liability reasons if no other.

And add to the margin of safety other considerations that effectively reduce load limits such as a driver's skill, reaction time, experience and so on

Sort of agree.  But that's a different argument than suggesting we should always subtract 20-25% from the tow rating.  So I'm not sure my wife will ever be driving while we're towing the trailer (just as she only rarely ever drives when towing our boat).  If she does, it will be in ideal conditions (in terms of traffic, roads, wind, etc).  But I don't think the trailer load as a percentage of max rating is really the import factor in determining whether or not she should be behind the wheel.

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Post Options Post Options   Quote campman Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2021 at 11:02am
Good day all. As a new person on this forum I have read a lot of the threads regarding towing, and towing safely. This particular thread already has a lot of points being made from both sides.

I think we all can agree manufacturers have provided reams of information regarding their vehicles and trailers for us to follow, though it can be difficult to discern exactly what to do (when towing a trailer in this case) in every circumstance. From what I have learned plus from my own experience, a good guideline to follow as given by one of the other members in another thread here. My truck has a max tow weight given. This is un-useable as guidance as I don't tow with only myself in the vehicle. So the next and more useful max weight given is the gross allowed weight of both TV and trailer combined. For my F150 that is 14000 lbs. Subtract from that my max allowable weight for my truck (7050 lbs) which must include all passengers, fuel, hitch weight and cargo. That leaves me with a max trailer weight of 6950 lbs. This is almost 2000 lbs under my advertised maximum tow weight capability. (My ordered 192 is estimated to be about 5000 lbs).

The only way to ensure an operator is not exceeding their maximum combined weight (before purchasing a trailer is a good idea) is to weigh the TV with everything loaded in it at a scale as it is loaded for use...this includes passengers! There has been a weight calculator provided earlier for any that may wish to use it. Individual axle loading will also come into play when towing so again, refer back to the individual axle weights from the scale to ensure limits are not exceeded. If you have the weights, see what the remaining capacity of the vehicle is, both GCWR and the axle loading.

I have max towed with a 3500 lb tow capacity vehicle towing a 3500 lb trailer. I also had to reload the trailer to increase the tongue weight as initially it had almost no tongue weight (that was disconcerting on the road, to say the least!). We drove 2000 kms at no more than 80-90 kms an hour through the hilly twists and turns of the Canadian Shield. I learned and will not ever do that again!

So, to summarize I would suggest (as this is a forum, that is the most we can do to try and help one another) is for Markw, or any other person who reads this, is to load their TV as they would if they were heading to their favourite camping spot (love the remote site you pictured earlier by the way!) and run your vehicle through a scale. You know now where you are and how close you are to the vehicles maxx allowable weight as well as the individual axle loading. You have the FR generated tongue weights etc, but would instead prefer to use the weights given here from actual owners and their loaded tongue/gross weights. They reflect reality, especially those that travel light as well, and have removed unneeded fitted equipment as you suggested earlier) as they know they are close to their own max allowable weight restrictions. This will generally let you know if you will legally be able to tow what you want within the max allowable limits of your particular vehicles or not. I initially entered "safely", but believe that is not applicable as weather, road conditions and trailer incidents such as a blown tire can quickly change the situation to an unsafe one for all vehicles but especially those towing at their upper limit.

Sorry it is so long of a post, I hope I haven't confused myself or anyone else that has made it through it to the end.
Andy and Laurie
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Post Options Post Options   Quote lostagain Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2021 at 11:16am
+ 1 to campman.

Weighing as suggested and plugging the data into the calculator that OG has often linked is a good way to know how you stand weight wise.  
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Post Options Post Options   Quote pedwards2932 Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2021 at 12:49pm
Not being one to want to go to the CAT scales everytime I leave I have a base weight (3225 lbs) which was TT loaded with what I would take everytime.  Then I weigh what I am taking for the particular trip.  Then I use my shureline scale to balance the load to get my 350 lb tongue weight.  I never carry any water in the tanks. 
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Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2021 at 1:16pm
I think perhaps some folks here are just not getting the message I and others have been trying to get out there. Not sure why not, but let's try once more, keeping it really simple.

1)Look up the meaning of MCGVWR.

2) Go weigh your complete rig at a scale loaded for camping.

3) Get your MCGVWR off your driver's door jamb.

4) Report back both numbers.

If you don't know those numbers then you don't have any real data to discuss here.

Note that I never once mentioned trailer weight or tongue weight.
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Post Options Post Options   Quote Olddawgsrule Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2021 at 1:42pm
Mark, I haven't read all this, yet I see OG is asking the basic 'first step'. 

Hit the scales dude! You'll be happy in the long run for the effort. Check with your town, you may be able to get weighed for free. 
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