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

[Collyn]

Originally Posted by jcl

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.

I agree with your 'I continue to believe that the operator is the most important variable'. But that in this case that 'variable' is grossly incorrect.

In my opinion, the critical speed of that rig will almost certainly be far less than 100 mph - more likely around 60 mph.

Collyn

[gator.bigfoot]

Originally Posted by panamerican

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.

Dry weight on the trailer is 7200 lbs. Hitch weight is 750. I don't know where you get your numbers from. Towing capacity without WDH is 7700. Like I said MB is fully aware of all numbers.

[BayouBiker]

Originally Posted by jcl

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)

that's just it, Ford did not test a 13,000 lb trailer with an 1,800 lb tongue. They tested one with with a tongue under 1,300 lb. Thus tongue weight is the relevant limit and the example trailer is not at all suitable by Ford's guidance.

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.

Nonsense, Ford specifically excludes that trailer by their guidance.

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.

Now you're finally singing to the choir. Welcome! The OEM ratings often represent the best case for the easiest to tow class of trailer, generally flat utility trailers. Towing a tTravel Trailer one is limited by tongue weight rather than trailer weight so the formula still works adequately just as it did for the poorly chosen example.

[BayouBiker]

Originally Posted by gator.bigfoot

Dry weight on the trailer is 7200 lbs. Hitch weight is 750. I don't know where you get your numbers from. Towing capacity without WDH is 7700. Like I said MB is fully aware of all numbers.

GVWR is 10,000 so he seems to be in the ballpark. MB limits tongue weight to 770 lb by their guidance. I wonder what your trailers loaded for camping weights are. Surely you are not towing empty and dry, but nothing would surprise me.

[BayouBiker]

Originally Posted by jcl

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.

Nonsense. I responded they were all included in the model and that I used stock configurations because I did not have data for non-stock configurations to tune the model with and the people on this site were asking generally about the stock equipped vehicles so making adjustments to the inputs for tires and alignment setting did not make sense. Your question, like Gator was simply to discredit and sow doubt, it was not to inform.

[BayouBiker]

Originally Posted by Collyn

I agree with your 'I continue to believe that the operator is the most important variable'. But that in this case that 'variable' is grossly incorrect.

In my opinion, the critical speed of that rig will almost certainly be far less than 100 mph - more likely around 60 mph.

Collyn

Indeed, Collyn much closer to 60 mph than to 90 or 100. The best direct evidence for that is the tongue weight and ball geometry guidance.

[gator.bigfoot]

Originally Posted by BayouBiker

GVWR is 10,000 so he seems to be in the ballpark. MB limits tongue weight to 770 lb by their guidance. I wonder what your trailers loaded for camping weights are. Surely you are not towing empty and dry, but nothing would surprise me.

Jumping Jehoshaphat it's 3 am don't you sleep? But to answer your question, fully loaded I'm around the 8-8500 mark. Tongue weight stays the same 750. Whether loaded or unloaded. There were a handful of trailers like this made and I wish it wasn't the case, but that's the primary reason behind the Hensley.

[jcl]

Originally Posted by BayouBiker

that's just it, Ford did not test a 13,000 lb trailer with an 1,800 lb tongue. They tested one with with a tongue under 1,300 lb. Thus tongue weight is the relevant limit and the example trailer is not at all suitable by Ford's guidance.

.... Ford specifically excludes that trailer by their guidance.

Nonsense. Tongue weight for that trailer is only 1800 lbs when it is unloaded. All it takes to produce a 1300 lb tongue weight is biasing the trailer cargo loading to the rear. It would not be difficult to achieve a 10% tongue weight. Ill advised, but not difficult. Ford rates trucks for towing trailers based on tongue weights as the trailers are hitched, not based on spec sheets of empty trailers on the lot.

I am not suggesting that trailer be loaded in that way, just pointing out that Ford in no way excludes that trailer. But they should, based on it being 1.5 stories tall, 42 feet long, and not at all aerodynamic. It would be a beast to tow. But Ford rates the F150 to tow it. And leads the public to believe that an F150 can do it. Perhaps they would limit their rating based on trailer frontal area, but that is about powertrain loading and load factor, not stability. I haven't seen ratings based on the side area of the trailer, and propensity to catch the wind.

The tow testing standard and associated ratings are simply a way of comparing different vehicles, not a way of ensuring safety in operation.

Just look back at the first response after the photo of that trailer was posted. It was that sure, you can tow it, because tow rating. It is a widely held belief, I am not picking on the poster. But a far safer approach is to evaluate every combination, not to just read the spec sheet.

Once you accept that the manufacturer's tow rating is not an absolute, but simply a nominated number somewhere in the middle of the possible range, then it becomes reasonable to consider when one could go higher (low trailers with less propensity to catch the wind, or more aero dynamic trailers, etc) and when one should go lower (the converse). It even leads one to consider whether the manufacturer actually pushed the published rating higher (a key indicator is when they start listing maximum frontal areas for each model) and when they have set it lower (likely because they don't consider a higher rating to be a marketable feature).

[Countryboy59]

Originally Posted by Shiny16

I operate the machine that is a requirement of my job within the specs and limits set by the engineers that designed it. The kind of engineers that have degrees. The book learning kind. If I wanted to be an engineer I would have gotten an engineering degree.

I am a degreed engineer and a manager. I wouldn’t hire an engineer unless he/she had demonstrated “hands on” mechanical ability. I’ve seen too many who couldn’t think their way out of a paper bag.

[BayouBiker]

You have gone off the rails jcl. Your scenarios are not rational. Unreasonable, illogical arguments lead to faulty conclusions as you have done here. Sure they fit a multitude of trailer types and absolutely trailer and tongue weights are not the most technically accurate way to express towing, but they are easy to measure and understand. They represent the best case for the easiest trailer type to haul and are the upper limits so in that sense they are absolute. More difficult trailer to haul cannot be reasonably fashioned and end up with a lower net size an weight primarily to stay below tongue limits. This is the elegance of the two number system, while technically imperfect it results in sound conclusions as long as the owner behaves rationally.

This latest argument you are making, as irrational as it is, also destroys your case though because nothing about it leads to a conclusion that one towing with a travel trailer can safely ignore both tongue and GTWR which is the argument you previously had ben making.

[gator.bigfoot]

Originally Posted by Countryboy59

I am a degreed engineer and a manager. I wouldn’t hire an engineer unless he/she had demonstrated “hands on” mechanical ability. I’ve seen too many who couldn’t think their way out of a paper bag.

Well put.

[walker]

Originally Posted by gator.bigfoot

Jumping Jehoshaphat it's 3 am don't you sleep? But to answer your question, fully loaded I'm around the 8-8500 mark. Tongue weight stays the same 750. Whether loaded or unloaded. There were a handful of trailers like this made and I wish it wasn't the case, but that's the primary reason behind the Hensley.

My word, I give up. The “Peterbilt” camp is declared the winner. I’m just going to haul my AS on my lowboy to the RV park and call it a day. Life’s just to short......

[franklyfrank]

Originally Posted by jcl

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

Huh ?
Your response makes no sense.
Advice and consultation is part of the sales pitch.

[BayouBiker]

Originally Posted by gator.bigfoot

Jumping Jehoshaphat it's 3 am don't you sleep? But to answer your question, fully loaded I'm around the 8-8500 mark. Tongue weight stays the same 750. Whether loaded or unloaded. There were a handful of trailers like this made and I wish it wasn't the case, but that's the primary reason behind the Hensley.

Yes, it is a good thing you are running a Hensley or ProPride. At 8500 lb (over the MB limit by the way), and 750 lb tongue (the Hensley weighs 150 so you are actually near 870 effective tongue weight (again over MB guidance), that trailer is capable of initiating sway at less than 50 mph. Even the Hensley may not save you on a steep downgrade and a sharp corner (say at or less than 50 mph truck guidance) in a bit of a crosswind and/or if you brake or decellerate suddenly.

I honestly don't understand why people would advocate these setups to people new to towing....

[GCinSC2]

Originally Posted by Countryboy59

I am a degreed engineer and a manager. I wouldn’t hire an engineer unless he/she had demonstrated “hands on” mechanical ability. I’ve seen too many who couldn’t think their way out of a paper bag.

Last year before RETIRING! we had a mechanical engineering intern work with us in an automotive aftermarket industry. I was installing a new clutch in my personal truck before leaving. "Mgr" engineer asked me to take intern under my truck and show him the installation. Both were Moccasin office shoes and kakis type. Me I wear boots, always.

Intern, I asked please go over to THAT workbench and bring me the BFH.

Huh what's that.

Just stay out from under my truck and watch from the edges.

Gary

[Shiny16]

Originally Posted by jcl

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.

No it was not a good example as that trailer exceeds Fords guidelines for any F150.

[gator.bigfoot]

Originally Posted by BayouBiker

Yes, it is a good thing you are running a Hensley or ProPride. At 8500 lb (over the MB limit by the way), and 750 lb tongue (the Hensley weighs 150 so you are actually near 870 effective tongue weight (again over MB guidance), that trailer is capable of initiating sway at less than 50 mph. Even the Hensley may not save you on a steep downgrade and a sharp corner (say at or less than 50 mph truck guidance) in a bit of a crosswind and/or if you brake or decellerate suddenly.

I honestly don't understand why people would advocate these setups to people new to towing....

Boy you really are full of it. I've towed all over NA with it. Down the 120 all across the midwest east coast umpteen times. No sway most of that done 65 to 70 mph. At 8500 with the WDH I'm still within the limits of the vehicle. The tongue weight gets distributed as well.

[mythbuster88]

Originally Posted by GCinSC2

Last year before RETIRING! we had a mechanical engineering intern work with us in an automotive aftermarket industry. I was installing a new clutch in my personal truck before leaving. "Mgr" engineer asked me to take intern under my truck and show him the installation. Both were Moccasin office shoes and kakis type. Me I wear boots, always.

Intern, I asked please go over to THAT workbench and bring me the BFH.

Huh what's that.

Just stay out from under my truck and watch from the edges.

Gary

Which BFH did you mean? I had to look up acronyms and this is what I got:

BFH
Big F***ing Hammer
BFH
Bacacheri Airport
BFH
Benign Familial Hematuria
BFH
Benign Fibrous Histiocytoma
BFH
Bitch From Hell
BFH
Baby Friendly Hospital + 1 variant
BFH
Ballenger Field House
BFH
Ballet Folklorico Huehuecoyotl
BFH
Barrel, Forged, Hammer
BFH
Basaloid Follicular Hamartoma
BFH
Bastard From Hell

[BayouBiker]

Originally Posted by gator.bigfoot

Boy you really are full of it. I've towed all over NA with it. Down the 120 all across the midwest east coast umpteen times. No sway most of that done 65 to 70 mph. At 8500 with the WDH I'm still within the limits of the vehicle. The tongue weight gets distributed as well.

I get that you are impervious to reason, these posts are not for you, they are to allow others considering the same to have second thoughts. I have no doubt you think your towing experience has been stellar and vindicates your disregard for MB towing guidance and the purpose for them. The fact you have a Hensley hitch though speaks volumes of what you truly think of the GL capability to arrest sway. You and I both know it is the hitch and not the vehicle keeping sway in check and it will as long as articulation angle remains small. If you drive carefully the angle will remain small, but an inexperienced driver may not be so fortunate. You should also read my post more carefully though, I didn't forecast you would experience sway in normal driving conditions. Finally you are not within the MB limits, you are over both trailer weight and tongue weight.

[jcl]

Originally Posted by Shiny16

No it was not a good example as that trailer exceeds Fords guidelines for any F150.

Which specific guidelines are you referring to?

Trailer weight? No
Resultant tongue weight after loading the trailer? No
Length? No
Height? No
Aerodynamics? No
Frontal area? Probably.

I haven’t studied F150 guidelines recently, so may be out on the above.

The point is, most here will focus on trailer weight. Then they will, or may, and should, consider tongue weight after loading. Most don’t consider the rest. If the manufacturer’s tow rating was performance or safety based, it would consider those factors.