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Old 01-28-2016, 12:16 PM   #61
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Audi Q7, Treg, Cayenne and Audi Q5 also use an OEM trailer hitch set up that utilizes rails inserted into the structural parts of the vehicle. In the case of the VW Audi Porch products, the support are not as long as the Merc but they are welded onto the trailer hitch and not bolted.



I had the factory hitch reinforced to eliminate flex that may occur due to the drop of the hitch receiver and increase my piece of mind when towing. My hitch reinforcement was done by Can-Am in London Ontario.
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Old 01-28-2016, 12:34 PM   #62
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Thanks for this clarification.

I am not an engineering, so can be ignorant in this topic. The fact that OE Mercedes hitch kit includes those 2 support arms does not mean for me that other German SUV have less stout hitch setup. Those support arms can be part of the chassis, can't they? In fact, I recall that BMW X5 E53 (2 generations back) had some kind of inserts as part of the hitch kit (similar concept to GL I guess, but the inserts were shorter). E70 (the next generations) does not have the inserts and I believe that they increased the towing capacity for E70 vs. E53. My guess is that there is some kind of reinforcement built in the chassis.
I am definitely not saying that Touareg's hitch connection to unibody is NOT stout -- I'm saying the Mercedes hitch unibody connection is more stout due to 2 large support arms. I'm not an engineer either, but that's just simple physics.

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Originally Posted by KSA63 View Post
Audi Q7, Treg, Cayenne and Audi Q5 also use an OEM trailer hitch set up that utilizes rails inserted into the structural parts of the vehicle. In the case of the VW Audi Porch products, the support are not as long as the Merc but they are welded onto the trailer hitch and not bolted.



I had the factory hitch reinforced to eliminate flex that may occur due to the drop of the hitch receiver and increase my piece of mind when towing. My hitch reinforcement was done by Can-Am in London Ontario.
I believe that's a Q5 hitch (not a Q7). Current Touareg/Q7/Cayenne's hitch does not have the bars. Hitch is only connected to unibody via 8 bolts.
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Old 01-28-2016, 12:44 PM   #63
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Great T/C/Q hitch & towing info guys!

And the last pic of the Audi hitch explains why there are 2 bumper bars in the Porsche parts catalogs - 1 for without hitch & another with hitch!

So apparently if retrofitting the Cayenne's hitch tow option, we should be buying both the bumper bar & hitch parts for the correct installation!

cactus - FYI - Andy T. had said on my other topic thread asking about issues with Cayenne S's for towing, that he didn't feel that I'd need to reinforce for our 1960 Avion T20, since it's only about 3-3500 lbs. wet & loaded - & even if it went to 4-4500-ish (vintage AS & kin are much lighter than todays' TTs).

So I think it depends upon how heavy the TT is.

Also, as noted above, a large drop or rise from the receiver may also impart more of an angular load on the hitch, so that too may be a foctor in deciding to reinforce.

PS - I think that MBZ G-range hitch reciever set-up is well thought out, but I'm not sure if the smaller mid-sized M-line (& whatever they've renamed it to now) is the same or similar design. The one shown would help transfer the WD torque load forward in the unibody very well though.

The mod with the drag strut type extension which CanAm does operates under the same concept of getting the forces moved up forward at the rear axle area, from what I've seen.

PSS - To clarify, my earlier comment about the Euro hitches being the same was in reference to their hitch OEM suppliers being that group noted above - not that they were all necessarily the same design. That said, I'd talked to an early M-320 owner who said his hitch was almost the same design as in the Touareg & Cayenne, but I don't know how similar nor if it changed to the type posted above for the G-series.

Cheers!
Tom
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Old 01-28-2016, 12:47 PM   #64
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I am not trying to negate what you are saying. I am just wondering whether other German SUVs have some kind of support arms built into chassis. If not, I agree that GL hitch looks very stout. I am even more happier about this as most likely GL will be my next TV. Just waiting for BMW X7 to be launched in two years. If I do not like it, GL will replace X5.
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Old 01-28-2016, 12:49 PM   #65
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Any idea whether the 2017 Touareg will be longer like the Q7?
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Old 01-28-2016, 02:27 PM   #66
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As long as we're guessing about stoutness of w.d. hitch mounting, and why Mercedes GL has no advisory not to use a w.d. hitch and VW does, I'll guess VW Touareg does not need the extra length of the retrofit OEM hitch. And Touareg's w.d. hitch advisory is because they are built in Europe where w.d. hitches are illegal, GL is built in America where they are legal.

My other concern though, would be twisting of the crossbar on any vehicle hitch from the vertical lift of a w.d. hitch combined with dynamic loads. This twisting as well as the side attachment has been addressed with a reinforcing steel bar welded to the receiver and forward under the vehicle. Probably good insurance against both issues.
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Old 01-28-2016, 03:12 PM   #67
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Quote:
I believe that's a Q5 hitch (not a Q7). Current Touareg/Q7/Cayenne's hitch does not have the bars. Hitch is only connected to unibody via 8 bolts.
You are correct, when I researched the purchase of my Q5 OEM hitch I guess I convinced myself that the hitches were the same across the VW SUV fleet, I was wrong. That said, the Touareg hitch looks pretty darn solid.

Also, I DO understand that you are not saying that it isn't.

Cheers,
Kevin
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Old 01-28-2016, 03:13 PM   #68
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Originally Posted by dkottum View Post
As long as we're guessing about stoutness of w.d. hitch mounting, and why Mercedes GL has no advisory not to use a w.d. hitch and VW does, I'll guess VW Touareg does not need the extra length of the retrofit OEM hitch. And Touareg's w.d. hitch advisory is because they are built in Europe where w.d. hitches are illegal, GL is built in America where they are legal.

My other concern though, would be twisting of the crossbar on any vehicle hitch from the vertical lift of a w.d. hitch combined with dynamic loads. This twisting as well as the side attachment has been addressed with a reinforcing steel bar welded to the receiver and forward under the vehicle. Probably good insurance against both issues.
I don't think the country of origin has anything to do with WDH being allowed or not. BMW X5 is built in America, and it advises against using WDHs.

There was a thread a while back, where the issues with the hitch reinforcement was discussed in detail. The gist of it was that welding a bar between the hitch (which is attached to the unibody, and cannot move) and the axle carrier (which is not attached to the unibody, and can move freely) does not make any sense.
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Old 01-28-2016, 03:26 PM   #69
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Originally Posted by bono View Post
Thanks for this clarification.

I am not an engineering, so can be ignorant in this topic. The fact that OE Mercedes hitch kit includes those 2 support arms does not mean for me that other German SUV have less stout hitch setup. Those support arms can be part of the chassis, can't they? In fact, I recall that BMW X5 E53 (2 generations back) had some kind of inserts as part of the hitch kit (similar concept to GL I guess, but the inserts were shorter). E70 (the next generations) does not have the inserts and I believe that they increased the towing capacity for E70 vs. E53. My guess is that there is some kind of reinforcement built in the chassis.
The E53 platform (2000-2006) included similar inserts installed into formed rails in the rear of the unibody, and they were bolted in more than one plane. The E70 (2000 onwards) does not have similar inserts, but the unibody is different as well. They didn't increase the towing capacity to my knowledge. I don't think we can conclude that the E70 OE hitch is as strong as the E53 is, we simply don't know. Perhaps they simply reduced the safety factor, given that they don't allow additional tongue weight with WD in any case. Certainly the E53 was overbuilt, but nicely so.

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Old 01-28-2016, 03:36 PM   #70
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I might be wrong, but I thought the E53 was rated to 6,000 LBS (and 5,300 LBS with smaller engines) where E70 is rated to 7,700 LBS (except for the US where they say 6,000 LBS).
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Old 01-28-2016, 03:50 PM   #71
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I don't think the country of origin has anything to do with WDH being allowed or not. BMW X5 is built in America, and it advises against using WDHs.

There was a thread a while back, where the issues with the hitch reinforcement was discussed in detail. The gist of it was that welding a bar between the hitch (which is attached to the unibody, and cannot move) and the axle carrier (which is not attached to the unibody, and can move freely) does not make any sense.
I agree that the country of origin (manufacturing) has little to do with WDH recommendations. I think that where the design engineering is done, and which marketing organization is involved (as they write the manuals and employ their own lawyers) matters though.

I recall the thread you mention. Here is a link to it.

http://www.airforums.com/forums/f463...-138296-4.html

I don't recall any consensus about attaching a strut to the rear subframe/rear axle carrier not making any sense. Some felt it didn't make sense. Others thought the point was being overplayed. The only evidence we had was from the many successful installations done by hitch shops and owners.

The rear subframe/rear axle carrier does not move freely as you claim it does. It is vibration mounted, but not free to move. If it was free to move, the vehicle would handle very poorly, as it would self-steer over bumps and around corners. Or the vehicle would fall down around it. Within the rear subframe, the differential itself is soft-mounted, but nobody is recommending a brace be attached to the differential AFAIK. It wouldn't make sense to soft mount the differential if the subframe was already soft mounted. See the attached photo for the E70 version.

If you want to buy the higher performance version of many BMW vehicles (similar to many European vehicles), or install aftermarket suspension modifications, you get stiffer or even solid mounts for the rear subframe. The question is whether you need to install those stiffer mounts when attaching a brace, or whether the range of motion is so small as to be inconsequential. Given the geometry of the brace, and the tab mount, it seems that the forces on the subframe at the brace attachment point would be predominantly downwards. Just like the weight of the vehicle pressing on it. In other words, what it is designed to take.

Jeff
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Old 01-28-2016, 04:06 PM   #72
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I might be wrong, but I thought the E53 was rated to 6,000 LBS (and 5,300 LBS with smaller engines) where E70 is rated to 7,700 LBS (except for the US where they say 6,000 LBS).
The E53 was rated 6000 lbs most places, 5000 lbs with the 3.0 and the 5 speed automatic (it wasn't an engine limitation, as the 3.0 manual was rated 6000), and there was a Euro option code for 7700 lb tow rating, on a 12% gradient, but you needed 18" wheels as well IIRC. That higher tow rating was a no charge option. From memory, it included an air scoop to direct cooling air to the diff, but I don't think there were other mechanical changes. It was a lot of years ago.

The E70 was rated differently around the world based on which geographic marketing organization was selling it. BMWNA (which is just the US) and BMW Canada use 6000 lbs, and I believe BMW Australia does as well. Note that the dealer channel hitches are being supplied by those organizations, not by the factory, and that was the rating of the hitches. There is a suspicion that the rating is dependent on the receiver spec. Certainly on my E53 there was no factory tow rating on the door plate or owner's manual; the only tow rating was in the receiver kit and instructions, and that included a decal to apply to the vehicle. Much of the rest of the world seem to just follow the BMW spec used in Europe.

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Old 01-28-2016, 07:44 PM   #73
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Thanks Jeff!
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Old 01-28-2016, 08:20 PM   #74
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You could look at this tow rating discrepancy in two ways:

1) X5 is truly rated at 7700# and BMW North America and Australia's sales and marketing has down rated the tow rating to 6000#,

OR

2) X5 is truly rated at 6000# and BMW Germany's sales and marketing has up rated the tow rating to 7700#.

What I know is that X5 is manufactured in the USA, and I doubt there are any 7700# campers sold in Germany.
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Old 01-28-2016, 08:47 PM   #75
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And what is your point with the campers in Germany?
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Old 01-28-2016, 09:05 PM   #76
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You could look at this tow rating discrepancy in two ways:

1) X5 is truly rated at 7700# and BMW North America and Australia's sales and marketing has down rated the tow rating to 6000#,

OR

2) X5 is truly rated at 6000# and BMW Germany's sales and marketing has up rated the tow rating to 7700#.

What I know is that X5 is manufactured in the USA, and I doubt there are any 7700# campers sold in Germany.
The Euro rating is supported by technical service bulletins, parts books, and so on. Even a test protocol for the 12% grade test.

The North American rating of 6000 lbs, at least for my X5, was on a label supplied with a Westfalia manufactured hitch kit, sourced by that sales and marketing department and not by the BMW manufacturing process.

The vehicle is built in the US with components from around the world. The design and development engineers are in Germany.

There are lots of reasons to downgrade a tow rating. Just ask a manufacturer of minivans, such as Honda.
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Old 01-29-2016, 02:21 PM   #77
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There is a German TUV (their DOT) test protocol for towing & hitch ratings which has been in effect at least since the 1980's which has specific tests for up & down grades to pull & brake adequately (I'd found one for the Porsche 928's factory hitch/tow ratings).

It was just a few years ago the they started an SAE test for rating them in the USA - I don't recall the protocol name/number, but it's listed as the basis for the Porsche Cayenne's tow rating in their manuals, TSBs, sales materials, etc. It started as voluntary until a certain mandatory date (I don't recall date - if any), so I think many of the other SUV mfgrs. are necessarily using them.

The Treg & Cayenne (& I assume Audi too) uses that type of vibration isolated rear suspension sub-frame as in the pic in the post above.

One of the Porsche dealership factory techs with whom I spoke last year did express concern that the strut from the WDH to that frame may cause early deterioration of those synthetic rubber isolator bushings, which would then need to be replaced, since they may flex more while under WD loading.

Similar wear may occur on other vehicles with that WDH set-up & suspension sub-frames.

That said, towing - especially larger/heavier trailers & for more miles &/or on rough roads/off-road - will cause more & faster wear on any wear components of any TV - even the big ole trucks!

This is a great discussion & very helpful info., but I'm concerned that we've strayed from the OP's initial question & purpose, but I don't have a suggestion for a better & more universal thread for this great info. where owners of all the various Euro TVs can find it.

Any ideas?

Cheers!
Tom
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