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Old 08-19-2015, 05:54 PM   #43
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Ok, here is some data. Sorry the post is so long. The data is for a unibody vehicle built by Toyota. It isn't rated high enough for an Airstream, but the principles are exactly the same, and Toyota models appear frequently in towing limit discussions.

Your premise appears to be that the manufacturers' recommendations on tow limits represents an upper limit that is grounded in engineering and can't be exceeded.

True story. We helped our daughter buy a small Toyota. I read the owner's manual. It said, on two consecutive pages:

American models: your vehicle is not designed to tow a trailer. Don't do it. Do not attach a hitch as the vehicle is not designed for this purpose. It went on in this vein for the rest of the page. Lots of red block print in large font sizes.

Canadian models (next page): maximum trailer weight is xx. Maximum tongue weight is yy. Respect the vehicle GVWR. Tongue weight must be included in your payload. If you install a hitch, be sure to use the one available from your Toyota dealer as it has been engineered to fit your vehicle. It went on for several pages. This is the most I remembered, so I looked it up today, and the tow limit was 700 lbs.

I checked the owner's manual for the same vehicle on the Toyota UK web site. Same vehicle, but optional engines that are all smaller and with lower hp than the U.S. and Canadian engine. Vehicle is built in the same factories. Tow rating was 2315 lbs, with a higher tongue weight limit. Around 1600 lbs with the smallest three cylinder engine available. The owner's manual went on for many more pages, and included GCVWR figures, a discussion of brake controllers with braked and unbraked trailer max weights, a discussion of load equalizing hitches, and so on. For a load equalizing hitch they recommended returning the front axle to unloaded height. And in case you didn't want to buy the Toyota hitch, it included a drawing of the factory engineered mounting holes in the unibody, with three options of which ones to use for your own aftermarket hitch, with bolt hole spacing for each choice. The manual was an international version, because it noted that towing was not recommended for South African models.

So, there is some data. A U.S. consumer could be forgiven for thinking that the vehicle wasn't designed to tow, because that is what the Toyota US marketing department told them. But apparently Canada is different (insert Canadian joke) and in the ROW, the tow limit is more than three times the Canadian limit. All for the same vehicle. Three times. And more than double for a three cylinder model with half the hp of the North American version.

And before someone claims that UK trailers are lighter, or have less tongue weight, that is irrelevant. The tongue weight limits were clearly stated in the marketing department's literature. Separate issue. Trailer frontal area was not discussed.

So much for an engineering basis for the recommendation, and the assumption that the recommendation represents an absolute limit.

Jeff

Jeff - thanks - that was a good explanation. I still don't subscribe but I really appreciate the insight.

I also appreciated the comment about the Marketing department with differing numbers on the same vehicle sold in 3 different countries.

Do we know whether there are actually any manufacturing differences in the product as distributed in different countries? Are suppliers different for some components or sub assemblies? Are materials different? Surely regulations are different.

I'm not discounting your view of the Marketing impact - but am also wondering whether there are any real differences or other reasons those recommendations are made by the manufacturer.

Other non-materials related reasons could certainly include the litigious appetite of these countries as well. It is entirely possible they choose to make the recommendation as a business decision to limit corporate liability. Plausible enough.

What do you think? Thanks!
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Old 08-19-2015, 06:08 PM   #44
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My Subaru has a higher tow rating in Europe. Over there it comes with rear load leveling suspension and a diesel engine -- none which are offered in North America. So, the same vehicle in different countries does not necessarily have the same specification. Even if the vehicles are exactly the same, different counties have different regulations that affect the ratings.
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Old 08-19-2015, 06:28 PM   #45
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Jeff - thanks - that was a good explanation. I still don't subscribe but I really appreciate the insight.

I also appreciated the comment about the Marketing department with differing numbers on the same vehicle sold in 3 different countries.

Do we know whether there are actually any manufacturing differences in the product as distributed in different countries? Are suppliers different for some components or sub assemblies? Are materials different? Surely regulations are different.

I'm not discounting your view of the Marketing impact - but am also wondering whether there are any real differences or other reasons those recommendations are made by the manufacturer.

Other non-materials related reasons could certainly include the litigious appetite of these countries as well. It is entirely possible they choose to make the recommendation as a business decision to limit corporate liability. Plausible enough.

What do you think? Thanks!
I don't personally know what the differences are in sub components with the non North American Toyotas. But I know that the statement "not designed to tow or to have a hitch installed" is not strictly speaking true. The discussion about weight distributing hitches and pre engineered hitch attachment points pretty much kills that argument. I don't know what the true upper maximum tow limit is, but I don't agree that it is zero as Toyota tried to tell its customers in one market. Note that we have many harmonized vehicle regulations between the U.S. and Canada.

With the BMW X5, my vehicle did not have a tow rating or GCVWR when I bought it. Nothing in the manual or door sticker. But BMW Canada sold a 6000 lb rated hitch for it, so that was the de facto rating. The same vehicle in other parts of the world had a 7700 lb hitch sold by the local BMW distributor, and an optional higher rating, which was a no cost option. I wondered, so I went to the Euro and North American X5 parts books, all available on line and searchable. I went down to cooling systems, axle ratios, differentials, etc. They were the same. So it seemed that the 6000 lb rating was somewhat arbitrary. The GVWR and axle load ratings weren't, to be sure. And I wouldn't want to blindly exceed the 600 lb tongue weight limit without some further investigation, and possibly a modification.

I think litigation fears are a part of it. Note that marketing isn't usually global, but rather regional, so marketing departments is plural. But engineering is global, at least for the examples given.

Jeff
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Old 08-19-2015, 07:35 PM   #46
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I liked the old Forest Service link too that's why I included it ... also because it says not to exceed the vehicles rating.
I have nothing against towing with a unibody.
Exceeding the weights specified (which initially are set by engineers and rigorous testing to see when it will break) no thank you - there is no such thing as magic math in the world of engineering,
Last, if nothing else, as a first responder I don't want to have to clean up the mess when the TV finally fails and a wadded up beer can goes tumbling down the road with a trailer chasing it.
Happy trails ...
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Old 08-19-2015, 07:53 PM   #47
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Exceeding the weights specified (which initially are set by engineers and rigorous testing to see when it will break) no thank you - there is no such thing as magic math in the world of engineering,
What sort of rigorous testing in the example above do you imagine was used by engineers to reduce a tow rating to zero based on the purchaser's delivery address? Or to increase it by three times when a smaller, lower power engine was installed?

As an engineer who has worked on vehicle design, maybe we should stop assuming that those sorts of decisions are all made by engineers.
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Old 08-19-2015, 08:18 PM   #48
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I would think the auto manufacturers would rigorously test any vehicle with a meaningful tow rating (say > 4500#). I know Toyota runs J2870 tests on its trucks, and most its SUVs (even 4Runner with a 4700# tow rating). It does not make sense for Toyota to run J2807 tests on Camry as they are people haulers not TVs. The rating for these marginal vehicles may be different in different countries. You do not prove much by highlighting these discrepancies.
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Old 08-19-2015, 08:19 PM   #49
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Well there is that pesky word "initially" connected to the word testing (I don't doubt the lawyers can influence things) and that equally troublesome proving that a Toyota model sold in the USA is identical (or not) to the same Toyota model sold in Canada which is also identical (or not) to the same Toyota model sold in England (etc.).
Perhaps I was just dreaming when a former brother in law computer geek took me to one of his work sites years ago where he set up the computers for tracking the new model testing by Ford for one of its pickups that never made it to production because it broke sooner than spec'd. Pity, it was a half ton diesel in 1995 - but maybe it was squashed for other reasons.
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Old 08-19-2015, 08:41 PM   #50
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Why would a car company build any vehicle ( unibody or body-on-frame ) to be "substantially stronger than necessary". In other words, why would GM build a unibody chassis heavier and stronger, to withstand loads imparted by towing, when the vehicle is going to be marketed as a passenger vehicle, and have a limited tow rating ? That makes no sense to me, to build something heavier ( which hurts fuel economy ) and stronger ( which costs more money for them to engineer and build ) when there is no added return for them.

Step the discussion up to pickup trucks: why would they build a class one truck that has class three capabilities ? Again, this makes no sense to me from an engineering or marketing perspective.

In my mind, it makes more sense for a car company to build vehicles targeted to specific market segments. Cars and minivans to haul people on a daily basis. Trucks to haul a load, or tow a trailer. The tradeoffs are fairly clear. For instance, a truck trades away some ride quality, and nimble handling to gain load capacity, higher pulling capacity, bigger cooling system, heavier duty brakes, axles, etc. It's a tradeoff the consumer willingly takes in order to have a vehicle that is more tailored to a specific task.

Why would we assume at the consumer level that it would make sense for us to "guess" that we know how all the decisions were made around the conference room table ? The table where engineering, marketing and legal all had their say.

In the end what we do know is that there is a specific limit stated by the manufacturer. It almost certainly passed muster with legal and engineering, and most likely also with marketing.

To take that to it's logical end, it's safe for us to say, if we operate the vehicle within the stated design limits, we are likely to have a greater likelihood of successful operation ( safety, reliability, durability ).
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Old 08-19-2015, 09:41 PM   #51
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The o.p.'s unibody Touareg was built substantially stronger than needed for passenger use because they are used throughout the world, and off-road use was also part of the criteria. It is rated quite high for towing duty as SUV's go, but towing was not the only design consideration.

The lowly unibody minivan has a measly 3500 lb tow rating but the chassis design is exceptional for towing Airstreams, very stable. And it is important to note Airstreams tow exceptionally well. It can carry a bunch of people safely and efficiently. Take out the bunch of people, reinforce the hitch receiver, and it is successfully towing Airstreams safely and efficiently. Lots of them, including some members on this forum and a few thousand others.

At some point it would be good to recognize this experience as valid and wonder why, rather than simply say they can't do what so many are doing. We could learn something.
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Old 08-19-2015, 10:04 PM   #52
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.. wonder why, rather than simply say they can't do what so many are doing...
I disagree with this statement. I know of only 2 members towing large Airstreams on this forum. I don't know of anyone that tows a large Airstream with a sedan on this forum. In the past 15 years, and thousands of miles of travel, I have never seen a sedan/minivan towing an Airstream or any other large camper for that matter. So, there are not so many of them.

I believe you mentioned that CanAm has set up 3000 minivans. 3000 minivans in the past 30 years is roughly 10 minivans per month. Ford/GM/Ram/Toyota/Nissan sell 200,000 trucks a month, and probably another 100,000 properly rated SUVs. 10 minivans a month vs 300, 000 properly rated vehicles is statistically 0.
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Old 08-19-2015, 10:05 PM   #53
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Doug, my friend....you are missing my point.
The truth is, you ( and some others ) are "guessing" the Toureg, or any of these vehicles were "designed beyond the stated limits". With all due respect, you cannot possibly know what those discussions were at the design stage, unless you were there in the room when these numbers were finally settled on.

But to my point, "if we stay within the stated limits", then we can infer that we are indeed more likely to have drivetrain reliability, be within chassis strength requirements, etc.

All the rest of this stuff is "guessing" in order to support a belief system of suitability.

I've said it before, and I'll say it again....if anybody out there wants to hitch the biggest Airstream ever to a Smart car and go towing, I really honestly don't care. I really don't, because from a practical standpoint, the probability of me personally crossing their path is infinitely small.
But to make "statements" based on idle "guessing" is doing a disservice to some of the new comers to towing. They may take statements to heart, and build their system around a flawed concept.
Over and out ( as always this has become the unibody/minivan vs the truck argument ).
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Old 08-19-2015, 10:37 PM   #54
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Old 08-19-2015, 11:12 PM   #55
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I would think the auto manufacturers would rigorously test any vehicle with a meaningful tow rating (say > 4500#). I know Toyota runs J2870 tests on its trucks, and most its SUVs (even 4Runner with a 4700# tow rating). It does not make sense for Toyota to run J2807 tests on Camry as they are people haulers not TVs. The rating for these marginal vehicles may be different in different countries. You do not prove much by highlighting these discrepancies.
The premise was that tow ratings are absolute limits, established based on engineering principles, and are dangerous to exceed. So now this only applies over a certain rating? What is the basis for that claim? Are these different engineers and different manufacturers?

The discrepancies being highlighted was that the vehicle was not designed to tow, and that it was designed to tow. It changed from year to year, based on US vs Canadian point of sale. The factory designed hitch sort of blows the theory that the vehicle wasn't designed to tow, whatever rating we follow. The ROW rating just shows the ridiculousness, when they have a rating over 3 times the Canadian rating. The point being debated is whether the ratings represent an engineering limit. Seems there might be other factors.
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Old 08-19-2015, 11:19 PM   #56
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... why would GM build a unibody chassis heavier and stronger, to withstand loads imparted by towing, when the vehicle is going to be marketed as a passenger vehicle, and have a limited tow rating ? That makes no sense to me, to build something heavier ( which hurts fuel economy ) and stronger ( which costs more money for them to engineer and build ) when there is no added return for them.
Why would the chassis loads for towing and carrying a load be mutually exclusive? The tow receiver attachment point, sure, but that can be reinforced in the aftermarket as was done for decades.

With my X5, there was a very rigid structure, big brakes, high performance. The things that made it a good high performance SUV also made it a good tow vehicle.
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