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Old 01-28-2016, 04:50 PM   #71
jcl
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Quote:
Originally Posted by rostam View Post
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, 05:06 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.

Jeff
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Old 01-28-2016, 08:44 PM   #73
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Thanks Jeff!
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Old 01-28-2016, 09:20 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, 09:47 PM   #75
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And what is your point with the campers in Germany?
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Old 01-28-2016, 10:05 PM   #76
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Quote:
Originally Posted by rostam View Post
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, 03:21 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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