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Old 03-29-2017, 03:53 PM   #421
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Originally Posted by rostam View Post
You can buy weight distribution hitches in Europe. They are not illegal -- I guess myths die hard.
Yes, you can buy them. You just can't use them on a vehicle built since 1998, and with European Whole Vehicle Type Approval for the vehicle itself, for tow vehicles up to 3500 kg and 8 passengers. See EU regulation 94/20 EC. You can use a weight distributing hitch on a non EEC vehicle you have privately imported, as an example. Or on a heavier commercial vehicle.

Since any current EU vehicle is going to have whole vehicle type approval, it isn't surprising that the engineers in these European countries will not recommend the use of weight distributing equipment. And in most cases, EU manufacturers do their design engineering in Europe, with only sales/marketing and in some cases assembly, done in North America.
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Old 03-29-2017, 04:07 PM   #422
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(...)
Touareg/Cayenne/Q7/X5 (European vehicles) are unibody vehicles and do not allow WDH.

BMW states not to use WDH only in the "Installation instructions". Nothing in the car manual or other sources. Just buy aftermarket hitch for BMW X5 and you will never see any warning about WDH.

It makes sense what they are stating in relation to their OE hitch design. The hitch has very long drop plates and based on the experience from those who used stock OE hitch, the plates may flex. Reinforcement of the hitch fixes the issue.


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Originally Posted by rostam View Post
(...)

Attached see a Touareg hitch. Its very stout. However, its connected to unibody via 8 bolts. Thats it. Applying WDH will put an immense amount of pressure on those bolts. I read somewhere on a VW forum that VW initially allowed the use of WDH, yet saw signs of stress in hitch unibody connection and disallowed WDH then. Now look at Mercedes hitch. It has 2 large support arms (highlighted) that go into a unibody recess and are bolted there. This is on top of the 8 bolts. These arms provides a stout hitch unibody connection and also provide leverage for WDH bars/chains.
BMW X5 (1st generation) manufactured in years 1999Ė2006 used also similar support arms as MB GL. Next generations of X5 kept the towing rating (in some cases increased the towing capacity) and are not using the arms.

Some may think that the support arms were integrated with unibody or are just not necessary taken into consideration stiffness of the chassis (which was in fact improved for BMW design from generation to generation).
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Old 03-29-2017, 04:30 PM   #423
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Originally Posted by bono View Post
BMW states not to use WDH only in the "Installation instructions". Nothing in the car manual or other sources. Just buy aftermarket hitch for BMW X5 and you will never see any warning about WDH.

It makes sense what they are stating in relation to their OE hitch design. The hitch has very long drop plates and based on the experience from those who used stock OE hitch, the plates may flex. Reinforcement of the hitch fixes the issue.
Agreed, but to clarify, only in the X5 E70 OE Hitch installation instructions. I have read the owner's manuals, and the workshop service manuals, and no references there to weight distributing equipment for any year that I reviewed.

My X5 E53 OE hitch kit instructions actually listed the same numerical tow ratings (tongue weight and trailer weight) for weight bearing, and weight distributing equipment, on separate lines.

And the E53 OE hitch kit for the UK, which had a swan neck hitch and no ability to use WD equipment, had the same chassis inserts as the NA version of the hitch kit.

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Old 03-29-2017, 04:42 PM   #424
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Those receiver hitch support arms only strengthen an otherwise too-weak unibody for the receiver. It may not be enough, check with the experts. They provide no additional w.d. leverage, they may strengthen the lever (somewhat), leverage is determined by the length of hitch ball to the steering axle.

Using a weight distribution hitch with the unibody has a simple solution, the solution generations of Airstreamers having doing. If the hitch receiver or body/frame is too weak, reinforce it. It's usually just a matter of extending a torsion bar from the receiver forward to near the rear axle. If the hitch recover is too weak and you are uncomfortable with reinforcing it, the tow vehicle may not work for you.

The hitch experts at Can-Am RV advised us they have reinforced about 250 Touaregs for weight distribution systems, most probably the best place to have it done, or ask them for advice on doing your own.
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Old 03-29-2017, 05:01 PM   #425
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All a WD hitch does is counteract the forces on the hitch receiver created by the trailer tongue weight. To the extent those forces are counteracted, the loads on the receiver will be lower.
The upward bending moment of the WD arms is much greater than the downward bending moment of the tongue weight, if one is restoring all or a portion of front axle load. A receiver that was nominally strong enough for a specific tongue weight (and didn't bend downwards) can still be bent upwards by then applying WD.
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Old 03-29-2017, 05:06 PM   #426
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Those receiver hitch support arms only strengthen an otherwise too-weak unibody for the receiver. It may not be enough, check with the experts. They provide no additional w.d. leverage, they may strengthen the lever (somewhat), leverage is determined by the length of hitch ball to the steering axle.
I can't comment on the MB, just the X5. The chassis strengtheners were very stout. As was the unibody. They do provide additional WD leverage because they widen the tripod, to borrow the terminology of Canam. They run forward from the receiver, and are bolted in multiple planes. Poster withidl who towed a 31 with his E53 for many years commented here that Canam didn't see the need to reinforce his OE hitch after inspecting it.
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Old 03-29-2017, 05:24 PM   #427
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The upward bending moment of the WD arms is much greater than the downward bending moment of the tongue weight, if one is restoring all or a portion of front axle load. A receiver that was nominally strong enough for a specific tongue weight (and didn't bend downwards) can still be bent upwards by then applying WD.
So you are saying that the receiver mount may not be designed for a torque in the opposite direction of a normal tongue load? I suppose that's possible. Still, you have to weigh the consequences of that against the consequences of having too low of a load on your steering axle.
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Old 03-29-2017, 06:47 PM   #428
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So you are saying that the receiver mount may not be designed for a torque in the opposite direction of a normal tongue load? I suppose that's possible. Still, you have to weigh the consequences of that against the consequences of having too low of a load on your steering axle.
Partly. It can be designed for a force in that opposite direction, that isn't a problem, but the magnitude is an unknown.That is likely the basis of some TV manufacturers recommending not to use WD equipment. The tongue weight forces are relatively simple to understand. But the moments created by WD equipment are tougher for the TV designer, since the manufacturer doesn't know how much WD will be applied, it is too variable. It depends entirely on the end user.

Some manufacturers who do support the use of WD equipment provide guidance. One manufacturer will say to use WD to return to unloaded front fender height, and design their receiver appropriately. Another will advise to return 50%, and this lets them design the receiver for lower forces.

I am not saying don't use WD equipment, as the consequences of a lighter front axle load are both clear and negative. But if the receiver and WD equipment combined can't restore front axle load due to flex, strengthen it. This has very little to do with unibody vs body on frame, especially since a unibody will typically be stiffer than a body on frame design, but much more to do with the strength of the receiver.
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Old 03-29-2017, 07:25 PM   #429
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I would probably use the WD hitch even if the manufacturer recommends against it. I will be safer. As to the receiver attachment to the tow vehicle, I would inspect it after use and look for deformation and cracked welds. Mechanical failures rarely occur suddenly. You will have the opportunity to strengthen it if necessary.
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Old 03-29-2017, 07:39 PM   #430
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When I check VW website on hitches everything says don't do anything until the 1D6 trailer prep pkg is installed. My vehicle data sheet says the 1D8 trailer hitch prep pkg is installed. Do I really need to have the 1D6 or dealer equivalent installed? I read in one thread that the 1D8 is all you need.
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Old 03-29-2017, 07:51 PM   #431
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No unibody vehicle (domestic, European, or Asian) has a receiver that supports 800# or more. Class IV and V hitches, however, are readily available to auto makers. The hitch weight limitation does not seem to be due to a sub-par OEM hitch receiver, but due to the chassis, suspension, etc.
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Old 03-29-2017, 08:21 PM   #432
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I don't see how they can sell a car they say can tow a 7200 lb trailer, and then they rate the hitch for 576 lbs max, and then they say you can't use a WD hitch. Basically they are saying you can't really tow what they told you you could.
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Old 03-29-2017, 10:40 PM   #433
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The Porsche engineers in Stuttgart have determined, using sound methods of engineering, testing, and analysis, that my Cayenne has a safe towing capacity of 7700lbs and a max tongue weight of 750lbs.
You sure about that second number? I have the same year Cayenne and mine's different.

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The Porsche engineers have also made it clear that one should NOT use a WD hitch with a Cayenne or Treg.
I have a Porsche and I've never seen documentation that one should not use a WD hitch. Source? Dave
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Old 03-29-2017, 10:55 PM   #434
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I don't see how they can sell a car they say can tow a 7200 lb trailer, and then they rate the hitch for 576 lbs max, and then they say you can't use a WD hitch. Basically they are saying you can't really tow what they told you you could.
You have to differentiate between what the vehicle is rated to tow, and what the hitch is rated for. Two different things. If you want to tow a North American trailer, with a heavier tongue weight than a Euro trailer, then the tow rating may be fine, but the hitch may need reinforcement to deal with the forces imposed by the WD equipment.
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Old 03-29-2017, 11:01 PM   #435
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No unibody vehicle (domestic, European, or Asian) has a receiver that supports 800# or more. Class IV and V hitches, however, are readily available to auto makers. The hitch weight limitation does not seem to be due to a sub-par OEM hitch receiver, but due to the chassis, suspension, etc.
A receiver rated for 600 lbs of tongue weight isn't necessarily sub par, it is just designed to a specific load specification. If one wants to apply more tongue weight, within the limitations of axle loadings, then buy aftermarket, or build one, or modify the existing one. Just as was done for decades before OE hitches were available.

Don't understand your reference to a Class V hitch, that is a marketing spin. SAE tow ratings only go up to Class IV.
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Old 03-30-2017, 06:18 AM   #436
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To put things into perspective: I towed a trailer with a loaded weight of 4473 lbs and a tongue weight of 678 lbs (15%) Florida to Alaska twice, over 25,000 miles, with a ML350 Bluetec using an Equalizer weight distribution hitch. The car's hitch label says I can pull 7200 lbs with a maximum tongue load load of 575 lbs, "weight carrying". I went under the car and inspected the hitch and its attachments and they're in perfect condition.
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Old 03-30-2017, 07:58 AM   #437
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A receiver rated for 600 lbs of tongue weight isn't necessarily sub par, it is just designed to a specific load specification. If one wants to apply more tongue weight, within the limitations of axle loadings, then buy aftermarket, or build one, or modify the existing one. Just as was done for decades before OE hitches were available.

Don't understand your reference to a Class V hitch, that is a marketing spin. SAE tow ratings only go up to Class IV.
The receiver ratings are decided based on multiple attributes of a tow vehicle, not just based on the axle ratings as allude. There is a reason VW does not put a receiver rated at 1000# on a Touareg, even though they have such receivers handy. Chassis strength, rear suspension, and stability of vehicle in emergency situations all come into play. There is some wiggle room of course (I doubt if you exceed the hitch ratings by 100# anything would happen, besides having less margin of safety), but you are getting into a gray area real fast.
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Old 03-30-2017, 08:44 AM   #438
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The upward bending moment of the WD arms is much greater than the downward bending moment of the tongue weight, if one is restoring all or a portion of front axle load. A receiver that was nominally strong enough for a specific tongue weight (and didn't bend downwards) can still be bent upwards by then applying WD.
Speaking of upward bending moment created by a WD hitch, the worst case of this is when the shank of an Equalizer or similar WD hitch bottoms out at 65 mph. This has happened to me a number of times on wavy roads. I contacted Equalizer about getting a shorter shank but they would have no part of it. I had to cut off 2" from the shank. Be very careful about your hitch clearance, even if it looks good when the car's not moving. Generally, do not use an Equalizer on a car or SUV where the receiver is generally too low to the ground.
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Old 03-30-2017, 10:19 AM   #439
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You sure about that second number? I have the same year Cayenne and mine's different.



I have a Porsche and I've never seen documentation that one should not use a WD hitch. Source? Dave
I looked up the towing capacity of the Cayenne on an internet trailer equipment site instead of checking either the hitch or ownerís manual. My mistake. The actual tongue weight for my 06 Cayenne, as posted on my factory hitch, is 616lbs. No problem. I am still under that.

I will send an email to Porsche Cars North America asking about the WD hitch restriction in hopes of getting information directly from the original source. The sources I have relied upon so far are my Porsche dealership mechanic and shop manager who installed the hitch, my independent Porsche mechanic, and a Porsche mechanic who frequents this forum.

To anyone who has done the math and chooses to add a WD hitch to their Cayenne so they can tow with a heavier trailer tongue weight, more power to you and I wish you happy camping. Just donít go around telling people towing normal loads that WD on a Cayenne is a necessity. It's not. Simply put, my braking and steering are incredible while towing. Adding a WD hitch when my trailer is either under or at the max tongue weight for my vehicle is only going to complicate the hitching process with no noticeable improvements to handling.

My final thoughts on the subject are that itís just silly to add a WD hitch to a Cayenne for towing loads within its rated capacity when a WD hitch is entirely unnecessary and the manufacturer says not to use one.
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Old 03-30-2017, 10:43 AM   #440
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Towing an Overlander I would be more worried about sway control than hitch weight. The dry trailer has 6.75% on the tongue, i.e., less than the commonly recommended 10-15%.
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