Audi RSQ8 towing 27' Globetrotter... Are we nuts or in love?

[gator.bigfoot]

Originally Posted by BayouBiker

As was mentioned previously, it is folly to apply European towing limits to American made travel trailers and North American road conditions. The European rating does not apply and are mathematically incorrect so by definition is nullified.

Mercedes suggests otherwise. Everything that was done plus the trailer weight they are aware of. They don't have an issue with this so why should I? The weight s are within axle ratings. The use of a WDH they actually endorsed. It's one of main reasons I bought the car. They told me they several customers that do the same thing and that the car could handle it.
So I think you might be the only one with the issue.

[panamerican]

Originally Posted by gator.bigfoot

Mercedes suggests otherwise. Everything that was done plus the trailer weight they are aware of. They don't have an issue with this so why should I? The weight s are within axle ratings. The use of a WDH they actually endorsed. So I think you might be the only one with the issue.

For my own knowledge, Gator, please share with me Mercedes Benz's official engineering literature where they state pulling a 9000-1000lb, 31' RV suggests their SUVs, powerful as they may be, with a roughly 118" wheelbase, is a good idea or falls under their factory stated limits in their USA/North American specifications. Just was on the MB site and the highest end GLE has tow rating TBD for 2021. The 450 is rated at 7500lbs. Please bear in mind that people in the vehicle, cargo, etc get deducted from that 7500lbs, so really best case say 7000lbs.

I would simply like you to provide me/us with written documentation from MB USA/North America that they fully endorse using their 450 or 580 to pull a 31' Airstream, with a roughly 1100lb hitch weight and nearly 10k lbs GVWR, with the car having roughly 500lbs in passengers and cargo. Please also share with me the info they state where modifying/welding as you describe is in their opinion is not only kosher, but increases the abilities of the Mercedes Benz vehicle.

If you can provide that in from MB, you will not only have my admiration, but you will also have clearly won the discussion, which I will cede to you.

If you are unable or unwilling to provide that, I would be happy to contact MB USA/North America for clarification.

I can tell you right now, that if I sent this same question to General Motors, after about a month of trying, I would be told, yes, our vehicle that you describe to us is designed to tow a 31' Airstream with a hitch weight of 1200lbs (with WD) and a GVWR of 10,000lbs as stated in our specifications (without modification to the vehicle).

I would further assume that in the event of an accident towing as stated in our viewpoints, sans the documentation to support it, the insurance carrier would have several questions for a setup exceeding manufac specifications. Of course, if you could provide to them what MB USA/North America stated that modifying the vehicle and/or the vehicle was rated for 1200lb hitch weight, 10k GVWR, then you and I would be in agreement and I would graciously cede the discussion to you.

[pteck]

Originally Posted by gator.bigfoot

Mercedes suggests otherwise. Everything that was done plus the trailer weight they are aware of. They don't have an issue with this so why should I? The weight s are within axle ratings. The use of a WDH they actually endorsed. It's one of main reasons I bought the car. They told me they several customers that do the same thing and that the car could handle it.
So I think you might be the only one with the issue.

The biggest difference and variable between Europe and the US has always been speed.

Lower max speeds is the reason why Europe has different hitch requirements. WD hitch primary advantage is in increase the margin of stability for additional speed.

[Andrew T]

If you want follow the line of logic that weight is all that matters and the manufacturers ratings are gospel then you can tow this 12,600 pound trailer with a properly equipped new F150.

[DewTheDew]

Originally Posted by Andrew T

If you want follow the line of logic that weight is all that matters and the manufacturers ratings are gospel then you can tow this 12,600 pound trailer with a properly equipped new F150.

If you do not put anything else in the truck then you could. 1,260 lbs is within payload of a range of F150 trucks.

[jcl]

Originally Posted by DewTheDew

If you do not put anything else in the truck then you could. 1,260 lbs is within payload of a range of F150 trucks.

Hmmm.

It is 42 feet long.

Over 13 feet high.

Square corners, the opposite of aerodynamic.

12,600 empty weight

Over 1800 lbs hitch weight.

You sure about that F150 recommendation? Even though it meets the tow weight criteria?

[jcl]

Originally Posted by BayouBiker

As was mentioned previously, it is folly to apply European towing limits to American made travel trailers and North American road conditions. The European rating does not apply and are mathematically incorrect so by definition is nullified.

If we extend that same logic, and note that the SAE towing test standard doesn't use a travel trailer, or a trailer as long as many Airstreams, then the SAE tow rating does not apply in many cases under discussion on this forum, and is mathematically incorrect. Nullified, to use your term.

Maybe we should get back to heeding the experts and not rely just on calculations and manufacturer's numbers.

[BayouBiker]

I completely agree that most vehicle manufacturers use low profile utility trailers and 10% tongue weight for the max limits. For that reason I suggest people reduce max capacity by 20-25% or not exceed the a tongue weight of 10% of the max rating which has just about the same effect. The same method can be applied to the European limits.

I suppose consistency on my part would require me to be more critical of the upper limits for the North American market.

[Shiny16]

Originally Posted by Andrew T

If you want follow the line of logic that weight is all that matters and the manufacturers ratings are gospel then you can tow this 12,600 pound trailer with a properly equipped new F150.

If you take Fords ratings for any F150 as Gospel then you would not tow the trailer.

https://www.ford.com/cmslibs/content...F150_Oct25.pdf

[BayouBiker]

Originally Posted by gator.bigfoot

Mercedes suggests otherwise. Everything that was done plus the trailer weight they are aware of. They don't have an issue with this so why should I? The weight s are within axle ratings. The use of a WDH they actually endorsed. It's one of main reasons I bought the car. They told me they several customers that do the same thing and that the car could handle it.
So I think you might be the only one with the issue.

I don't recall making any specific claim about your configuration, my comments are general comments about those who suggest it is Okay to exceed OEM towing limits, and tangentially about the original post scenario, though even there, I indicated the person may well be able to make it work, though it is close. As far as I know, you are below manufacturers guidance, but I don't know because I don't know or don't remember if you ever described you precise configuration.

[BayouBiker]

Originally Posted by Andrew T

If you want follow the line of logic that weight is all that matters and the manufacturers ratings are gospel then you can tow this 12,600 pound trailer with a properly equipped new F150.

Um I don't see where the F150 has sufficient tongue weight rating to pull that trailer when laden. I think most would agree that trailer should have a tongue weight of at least 1,700-1,800 lbs to be stable It appears Ford is specifically advising against this. You may want to use an example that fits within the ratings, your point might seem a little more credible.

[pteck]

Stability can come from more than just tongue weight. Some long time practitioners here have learned to use all the tools at their disposal.

As an engineer, I wouldn't for a moment try to discredit what others have accomplished. Even if that learning was done by way of different methodologies. Multiple ways to skin a cat and the proof is in the pudding.

Manufacturers recommendations have to straddle concerns and often have to suit the lowest common denominator. For example, even for those that may have trailer weight balance wrong, tire pressures wrong, overly projected hitch, WD out of whack, etc.

Use all those tools to your advantage, and turn all the right knobs, it's wholly possible to take things above and beyond.

After-all, that's how engineers do it. Take a good idea, solve problems, and make it possible.

[Collyn]

I suggest it is pointless to bring the associated maths into this discussion. What most people on this forum appear to wish to know is what size conventional TT can they tow at a realistic speed - and that is certainly not as high as 100 mph.

A simple and basic rule is the laden weight of the trailer does not exceed that of the tow vehicle. A second is to limit trailer length.

Do this (and by all means use that Hensley hitch) and you have no need for other stability 'aids' that mostly work only at low speed.

Collyn

[BayouBiker]

The trouble Collyn is that the original post and all of those defending going over OEM guidance have already given up on ideal towing configuration. They don't have much interest in what is best. They want to know what is the worst and least safe combination they can get away with and still maintain some reasonable and acceptable risk of catastrophe. How do you answer that question?

Edit: They also want to know what suspension, tire and hitch performance tuning tricks can they substitute for tow vehicle mass and wheelbase to accomplish the same effect and what trailer modifications can they make so the trailer has less effect than if left stock and loaded conventionally.

[jcl]

Originally Posted by Shiny16

If you take Fords ratings for any F150 as Gospel then you would not tow the trailer.

https://www.ford.com/cmslibs/content...F150_Oct25.pdf

Originally Posted by BayouBiker

Um I don't see where the F150 has sufficient tongue weight rating to pull that trailer when laden. I think most would agree that trailer should have a tongue weight of at least 1,700-1,800 lbs to be stable It appears Ford is specifically advising against this. You may want to use an example that fits within the ratings, your point might seem a little more credible.

I thought it was a good example.

Looked at another way, if we consider the claim that Ford has extensively tested the F150 to the tow rating that they rate it at, north of 13,000 lbs, oversteer and all, then Ford recommends that it is safe to tow that trailer, if one just reduces the tongue weight to 10%. Maybe some heavy ebikes on a bumper rack, for example. (Don’t do that)

I wouldn’t do it. I suspect most here wouldn’t. I don’t think Ford was considering the particular trailer in the example. But it illustrates the fallacy of considering that tow vehicle manufacturers’ tow ratings are some kind of gospel.

When I towed large boats, I had the opportunity to position the boat fore or aft on the trailer. And power boats had their significant masses in different locations than sail boats (aft vs centred) When I moved heavy equipment on a flat deck I slowed it way down. Car transporters have little crosswind sensitivity if not enclosed. And so on. The idea that a single tow rating can apply universally to the range of trailers out there is laughable.

[jcl]

Originally Posted by Collyn

I suggest it is pointless to bring the associated maths into this discussion. What most people on this forum appear to wish to know is what size conventional TT can they tow at a realistic speed - and that is certainly not as high as 100 mph.

A simple and basic rule is the laden weight of the trailer does not exceed that of the tow vehicle. A second is to limit trailer length.

Do this (and by all means use that Hensley hitch) and you have no need for other stability 'aids' that mostly work only at low speed.

Collyn

Would you agree that if a combination is stable at 100 mph, and in a range of real world conditions (side winds, etc), despite the trailer weighing more than the tow vehicle, that it is also likely to be stable at common tow speeds of 100 km/hr?

And by Hensley hitch, do you mean 3P, or pivot point projection, and not just the ones sold by Hensley? I haven’t used a ProPride, but they have their supporters.

[jcl]

Originally Posted by BayouBiker

I suppose consistency on my part would require me to be more critical of the upper limits for the North American market.

I think that is very well said.

[jcl]

Originally Posted by franklyfrank

Those shops are in business to make money.
Selling expensive hitches and shop work alterations is lucrative.
An easy sell to someone contemplating the purchase of an expensive TV.
8 years ago we bought or first AS a 28' International.
I was intreaged by an article in the Airstream pefiodical by CANAm showing that they are towing with modified Minivans.
Being in the Infrastructure construction business I spent my life worrying about overloaded trucks . So I sent of an inquiry to CANAM asking how do they compensate for payload.
I am still awaiting their answer.

Your fail is in assuming they charge for advice and consultations.

[jcl]

Originally Posted by gator.bigfoot

Knowing how to apply the math correctly would also help. I have asked you to supply the math behind your assertions. You have not. This can only mean one thing. If you want to lift yourself to be the towing gurru then, put some sort of proof to it. Otherwise you are no different than anyone else other than the people you seem to have an issue with. They're proof is in the product they provide. You can make all the arguments you want but you will always come up short. On a track comparison my money is with the other guy.

Originally Posted by BayouBiker

gator, there are a number of published, peer reviewed papers describing the physical matrix algebra and providing the transfer functions and determinate. ..... The solution formulas are excessively complex and cannot be written out in any way that would be meaningful to anyone. There would be no purpose, because nobody could check them to verify they are accurate anyway....

When I asked similar questions, I wasn’t interested in reproducing the calculations. I just wanted to know in general what sort of assumptions were made so that I could decide for myself what the relevance or significance of Brian’s theoretical calculations were.

When I found out that he didn’t consider several variables that I considered significant, I stopped asking. For the Euro SUVs, and all of the focus on oversteer, he didn’t consider TV tire variables (width, diameter, tire characteristics) For WD setup, he didn’t consider ball angle (tilt), conflating it with articulation angle. For the 3P hitches, I wasn’t clear on how he modelled them. He focused primarily on trailer weight without quantifying trailer length, or design features. He had widely varying opinions on the towing capabilities of different Euro SUVs that are reported to have similar towing performance characteristics.

So I stopped asking.

There may indeed be a nugget of truth in the oft-stated oversteer at the limit concern. But what hasn’t been qualified is that it matters. It is like the claim that the critical speed hasn’t been comprehensively tested for. If it is over 100 mph, I sort of don’t care, I don’t plan on approaching it. If oversteer tendency is increased by a small percentage in certain conditions, but won’t be an issue in normal operation or emergency evasive manoeuvres, it is kind of irrelevant to these discussions.

Every time I read that disaster is lurking just around the corner, I have trouble getting overly concerned. Experience hasn’t shown that to be the case. I continue to believe that the operator is the most important variable. For the equipment, that set up is critical. And claiming that one class of vehicle is the only way to do it safely is overstated.

I would tow the 27 with the Audi. With those tires, if they are rated for the axle load. But not without properly set up WD. And only with knowing the resultant axle loads.

[Collyn]

Originally Posted by jcl

Would you agree that if a combination is stable at 100 mph, and in a range of real world conditions (side winds, etc), despite the trailer weighing more than the tow vehicle, that it is also likely to be stable at common tow speeds of 100 km/hr?

And by Hensley hitch, do you mean 3P, or pivot point projection, and not just the ones sold by Hensley? I haven’t used a ProPride, but they have their supporters.

Re: "Would you agree that if a combination is stable at 100 mph, and in a range of real world conditions (side winds, etc), despite the trailer weighing more than the tow vehicle, that it is also likely to be stable at common tow speeds of 100 km/hr?""

As 100 mph is 160 km/h, it is likely to be less unstable at 100 km/h (62 mph). It is nevertheless far better to have that tow vehicle weighing much the same as the trailer. In essence, no trailer towed via an overhung hitch can ever be 100% 'stable' - unless towed by (an improbable) infinite mass.

I used the term 'Hensley' rather than 'pivot point projection' as I'd assumed most people in the USA will know what I mean. If not please advise.

Collyn