What it Really Weighs

Originally Posted by Mr. Adventure

"Physics is not a study of "guidelines", it a study of laws."
You're right. Engineering is a study of guidelines.


...you're still over the rated tow capacity of your TV."

The numbers show that my tow vehicle is rated to tow 4700# if the tow capacity is figured the way it's figured for your Astro. I'm within GVWR, GCWR, and all axle load limits.

Going back to one of my previous post, how many people would go out and buy a piece of rope rated at 3500 lbs and then knowingly hang their entire 4000 lb family over a cliff with it. Wouldn't you buy a piece of rope rated at 5,000 lbs if given the choice?
I can't imagine hanging my family over a cliff for any reason with any rope.

"For me, it is very "black and white" in that I would never tow beyond my rated TC...period."

I'd bet the price of a weigh ticket that I could find something, somewhere about your Astro, hitch, TM, and load that doesn't meet a spec somewhere. We all are safer on the road when our mental energy is conscious of the possible weaknesses in our rigs instead of finding comfort in "common sense" and the things we know for sure that might not always be really true.

There are problems with making manufacturer's tow ratings into laws. For openers, they are based on lots of soft information. Manufacturers don't do it the same way, and it's even possible that no manufacturer uses the sort of rigor that would need to be the basis of proper and enforceable laws. Some manufacturers overstate the limits, some are more conservative. We have no idea how limits were calculated or where the limiting factors are. We don't know what fudge factors are already in them. Tow ratings are meant to be guidelines, and are not suitable as the laws you might like them to be.

It turns out that different members of this board have some very different objectives in choosing their tow vehicles. Some want the best tow vehicle there is. Some want vehicles with special capabilities. I just want to be able to use the vehicle I want to drive to work every day, and ideally, a vehicle I already have.

"Many of today's so called SUVs are merely car chassis with a SUV body bolted on it, including mini vans. People have illusions that these types of TVs are "trucks", but there are not."
The type of chassis does not have anything to do with the engineering side of a tow rating, and I wouldn't expect the words "truck" or "SUV" to appear in any equations.

"I don't think bad practices should be condoned here. "

I have no problem with others' opinions or the tow vehicle decisions they choose to make. I have a problem with people projecting their personal opinions into laws and labeling those in violation as grossly negligent felons. This, to me, would be a bad practice.

I'll ask one rhetorical question: Is this board open to all TrailManor owners' experience, or only those whose tow vehicles are considered worthy by people who have strong opinions without any personal experience?

As I said, people are going to do what people are going to do....no matter what the facts are...

Originally Posted by wbmiller3

This thread reminds me a lot of discussions at work. What is really being talked about is 'margin' - the difference between the point you are operating at and the point at which failure happens. Adding margin is expensive and inconvenient. And, it is hard to know exactly where these two points are. I don't like running out of margin so I get an oversized tow vehicle and pay the price in upfront cost and operating expenses. Of course, I could sell the trailer and guarantee myself that I'll never have a towing accident but that is not acceptable either. So far when bad things have happened, I have always had adequate margin and no one got hurt.

Bill, the term is also know as "service factor", or "safety factory". In my profession, it's more commonly called service factory.

A common such "fixed" factor is with industrial hose....the factors double themselves.... working pressure x 2 x 2.
ie: If rated working pressure of the hose is 1000psi x 2 = 2000psi (minimum burst?) x 2 = 4000psi (burst). While 1000psi would be the max pressure for this hose, the real daily use pressure would actually be lower (ie: 800psi). The safety factors are built in in case of a surge, etc, so this max working pressure is doubled to 2000psi and is called "minimum burst". But in reality the hose is designed not to catastrophically fail until 4000psi. Of course you would never run 4000psi through this hose as a daily working pressure, much less plan to run 5000psi.

In the old days it was very common practice to simply use a 2x factory.... if the pump required a 100hp motor, you designed the drive for a 200hp. As computers made their debut and power sources and driven apparatus continued to get more diverse, the factor became much more concise. We use charts to look up the type of "driver" (electric motor, gas engine, diesel engine, number of cylinders, etc) and then the "driven" (centrifugal pump, reciprocating pump, fan, blower, etc), and finally the "time used" (start and stop constantly, start and stop intermittently, runs constantly, etc) to look up a precision service factor.
For example, if you have say a 3 cylinder diesel engine running a reciprocating pump that starts and stops constantly, the the service factor could be upwards of 2.5 or 3.0.
Now on the other extreme, if you have an electric motor driving a simple fan for 24/7, the service factor would probably be a 1.0, as this type of drive runs constant, doesn't change speed or torque, doesn't start of stop, it just runs smoothly and constantly around the clock.

There are many factors that effect service factor, but 1.0 is the lowest factor ever used (100hp = 100hp), but at the same time, rarely used. Of course there is no such thing as a "negative service factor" (as this would then become a "danger factor") You would never use a 100hp motor to drive a 150HP requirement. You wouldn't be in business very long for numerous reason.

I've often wondered how good these ratings are. My Tacoma's rear axle's GAWR is only 3110# but the Trailer's Dexter axle's GAWR is 3619#. I've opened up the Dexter axle and the bearings are pretty puny. And then there's that rubber band suspension compared to the Tacoma's leaf springs. Could the brakes be that different?

My gut tells me that auto manufacturer's are much more conservative in their ratings.

This topic just makes me wonder what the "service factor" was for the Apollo program.

Or brain surgery.

My son designs the frame for satellites. If it fails, it is not possible to repair under any circumstance. I wonder what he uses?

[wbmiller3]

In aerospace (my profession) the fight for margin often involves weight as well as cost. Our factor of safety is usually 1.4.

[Mr. Adventure]

Originally Posted by wbmiller3

In aerospace (my profession) the fight for margin often involves weight as well as cost. Our factor of safety is usually 1.4.

Many products are sold documenting their expected failure values. The "safe" working load of a nylon rope is supposed to be about 1:4, or for example 200# for 1/4" nylon rope that has a breaking strength of 800#. I've tested these numbers with 1/4 " nylon rope on occasion, and both of these numbers and the ratio between them are guidelines.

Cars, and apparently space vehicles, are delivered with a safety factor included in the way they're designed and delivered. We have no idea, of course, what the factors are in calculating tow ratings, but we know that the parameters are influenced by economic and durability factors beyond just the safety issues. A big one the manufacturers are afraid of is the transmission load from wind resistance on a full height travel trailer (though I would be concerned about it's road stability as well). My friend from the car business told me that they really do test vehicles towing trailers on the track. But we don't know much about either the precision manufacturers use in establishing tow ratings or their reliability, and it probably varies from manufacturer to manufacturer.

Adding an additional safety factor is laudable, but also expensive. We use these trailers in different ways and take them different places. It is necessary that our decisions be allowed to be different.

[ThePair]

Originally Posted by Mr. Adventure

Adding an additional safety factor is laudable, but also expensive. We use these trailers in different ways and take them different places. It is necessary that our decisions be allowed to be different.

Hear, hear!

Originally Posted by Mr. Adventure

Adding an additional safety factor is laudable, but also expensive. We use these trailers in different ways and take them different places. It is necessary that our decisions be allowed to be different.

Apparently I'm wasting my breath, but I'll repeat for those new users actually trying to make an educated decision...
You never exceed the TC of your TV, just as you would never purposely plan to run 4500psi pressure through a hose designed for 3500psi.
Most products have a "safety factor" build in, but it's not for you as a user to discount this to fit your needs.
Saying that I can tow 4500 lbs behind a TV that is designed for 3500 lbs is an accident waiting to happen.

[Mr. Adventure]

Originally Posted by ED-n-KEL

Apparently I'm wasting my breath, but I'll repeat for those new users actually trying to make an educated decision...
You never exceed the TC of your TV, just as you would never purposely plan to run 4500psi pressure through a hose designed for 3500psi.
Most products have a "safety factor" build in, but it's for you as a user to discount this to fit your needs.
Saying that I can tow 4500 lbs behind a TV that is designed for 3500 lbs is an accident waiting to happen.

"the term is also know as "service factor", or "safety factory". In my profession, it's more commonly called service factory."
You're confusing "safety factor" with "service factor". Service factor is additional margin added to allow for heavy or unusual uses that impact durability. Safety factor is about safety. These would presumably each be applied to the appropriate aspects of a design.

"Saying that I can tow 4500 lbs behind a TV that is designed for 3500 lbs is an accident waiting to happen"
My tow vehicle is rated for 3500# in the sales brochure, but has capacity in the GCWR for 4700#, the way Chevrolet would figure it. Therefore, by your standards, the accurate statement is that my vehicle was designed to to tow 4700#. Given that Toyota rates these vehicles as either 3500# or 5000#, the 3500# rating was properly applied.

"As I said, people are going to do what people are going to do....no matter what the facts are..."
I've honestly tried to get the facts on the table. You're trying to apply the way they rate hoses to the way they rate tow vehicles. Hoses are pretty black and white by comparison, with an unambiguous set of objectives, a lot fewer variables, and a comparatively straightforward process available to anyone wanting to stress them to see where and how they actually fail in the real world. A tow rating is much more complicated than that, and the most easily found evidence of "failures" in trailer towing I've been finding so far is about trailers that became detached from their tow vehicles (and there are so many of these stories in relatively easy Google queries that it appears there are many hundreds of events). At least one fact should stand, if we're not hypocrites and going to do this in black and white instead of gray: your hitch receiver is only rated for a 500# tongue, and you're probably above that, as most all of us are.

You're getting a Class IV hitch receiver before you tow again, right?

Originally Posted by ED-n-KEL

Apparently I'm wasting my breath, but I'll repeat for those new users actually trying to make an educated decision....

Note to new users.... as you can see, if you have read the post this far, ones choice of tow vehicle can be a most interesting and lively subject. Were even learning about the manufacture of rope, elevator cables, hydraulic hoses and space ships here... Just remember that however you go, go safe. Ask questions and do your own research to be able to make a informed decision that best fits you. But be safe first. Remember that however you go that trailer is going to be behind you every step of the way.