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Old 07-28-2015, 05:18 PM   #43
jcl
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Originally Posted by bono View Post
There are two questions I would like to ask again to understand the issues (or at least to try to understand):
Also for what it is worth, here is my opinion.

1) I don't think there is a substantive difference between square tube and rectangular tube for the strut. Whatever fits. I would choose to use a box section over a flat bar, but I don't have reason other than personal preference.

2) There are two types of reinforcement being discussed. Zetatre is correct in that the 2" receiver is not as solidly mounted to the cross bar on the E70 as on the E53. I think it needs reinforcing if substantial WD is being used. That could either be gussets to the cross bar, or a strut tied in to the vehicle further forward. The gussets help with any flex at the tow bar, but don't help in any way with the interface between the cross bar and the unibody.

We don't know that the E70 unibody is weak at this point. What we do know is that the E53 was very strong when the OE hitch was installed, and that hitch included chassis stiffeners that were engineered into the unibody at three attachment points on each side. The absence of those struts on the E70 makes it an unknown. It doesn't make it weaker, it is simply an unknown.

Since I would want to reinforce the receiver in any case, I would personally err on the side of caution and install a strut forward to address both issues. I don't know if that strut can be attached to the unibody, or just to the suspension carrier, based on clearances and access. But I would ask an installer such as Canam if they have experienced any drumming noise in the cabin after using the carrier as an attachment point, due to the new path that was established by the strut for noise transmission. If they have, I would look to the unibody itself. If not, I would use the carrier and not worry about it. I would bolt it to the carrier, and not just weld it, in the interests of future service access.

Hope that helps

Jeff
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Old 07-28-2015, 05:20 PM   #44
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Originally Posted by Widget View Post
Having an X5 with aftermarket receiver which was later reinforced can-am style, my vote if I could do it again would be to run the reinforcement strut forward to somewhere on the unibody vs. the rear suspension carrier. My personal logic is that while I don't seem to be any negatives at the moment from the can-am style'd mod a direct attachment to the unibody is less intrusive to the design intent of the vehicle.

Possibly I could have lived with the receiver flex, but the WD system works much better now that it is eliminated.
I agree that the attachment to the unibody directly is less intrusive to the design intent of the vehicle.

Interesting that the WD system works much better now. That suggests there was flex previously. It just comes down to whether that flex was all between the receiver and the cross bar, or also between the cross bar and the unibody.

Jeff
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Old 07-28-2015, 05:27 PM   #45
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The comment from Widget caught my attention too: what do you mean by the "WD works much better"? What have you noticed before and after?
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Old 07-28-2015, 11:12 PM   #46
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Thank you zetatre and jcl! My new hitch is on the way. Once I receive it, I will discuss with the installer whether it is possible to bolt the strut to the unibody directly. I will report back after the discussion.

Thanks!
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Old 07-29-2015, 08:15 PM   #47
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Originally Posted by zetatre View Post
The comment from Widget caught my attention too: what do you mean by the "WD works much better"? What have you noticed before and after?
I'll try to explain. "works better" is probably not the exact way to describe the situation so I'll be more detailed and explain the non-reinforced to reinforced observations with WD. To further aid, this is the aftermarket hitch I installed.

Hitch alone Observation: Didn't realize what was actually going on at first. The receiver started off nearly parallel to the ground. After the first couple trips I noticed it had an upward angle. Furthermore I realized I was needing another link hanging to get the weight back out the the front. About the time I decided to go one more link I took note that the receiver was angled up even more. Some of this movement was permanent in that under load the receiver maintained an upward angle. Applying the weight distribution I could watch the square portion of the receiver flex upward to the point where it was in solid contact with the underside of the bumper trim. I don't want to know what it looked like on the road. This much visual flex left me with an image of the trailer running away on it's own.

My Chosen Solution: I chose to reinforce can-am style to what I'll call the suspension carrier. The crossmember referenced earlier in the thread. Receiver angle was corrected and with a little welding & square tubing and I had a nice brace installed.

With Brace Observation: The receiver angle does not change or flex to any distinguishable degree. In my view the WD works better because there is not the variable of rotational flex occurring. Previously I had to apply tension to take up the flex and then transfer load. Now the force from the bars is transferred directly to the vehicle.

In both pre and post the wt was transferred, but tensioning bars to accommodate a flex or receiver angle that is slowly migrating upward didn't seem like a smart call. Maybe the migration would have stopped or was near the max, but it's goofy setting up the WD when you lose all your rearward ball angle compensating for the receiver angle.

My Conclusion: Further observation pre and post brace. If you observe the design of the hitch in my link above the area I believe to be flexing is the portion of the hitch which exits the mounting plates (flat portion w/ 4 bolt holes on each side) to the inside and perpendicular to them. At the uppermost corner where the steel bends from the plate to the outward fin I was able to detect movement. In resting position this was not in contact with the unibody when viewed through an open tailgate, but when Wt. dist was applied the radius area would flex towards and just touch the unibody.

To further test the hypothesis of where this hitch was flexing I inserted my cargo platform and had a person stand on the furthest edge while I felt the movement between the hitch and the unibody. My conclusion was that the upward flex of the receiver insert was a result of the hitch flexing vs. a body strength issue.

Caveat: I do get a good bit of rattle in my tailgate, but a bit of googling indicates this may just be a problem with age on the vehicle vs. an effect of towing. I've adjusted the bump stops once and corrected this issue, but never the less it came back.

100% my opinion - These are great vehicles to to smaller size units with 23' and under seems reasonable. 25' maybe.... But to do it you need to optimize the vehicle for your specific need, not the as the engineers designed for the masses. What percentage of X5 do you think see heavy towing duty? Heck, I bet we'd all be surprised to see a true number on 1/2 ton trucks. Ultimately I demanded more performance than the system provided, although I'm fully within all specs across the board. Post mod I'm a happy camper. The miles will tell if the chosen brace location was a good or bad call.
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Old 07-30-2015, 06:10 PM   #48
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Widget thank for the elaborate post!

I don't see any flex when I apply the WD on mine nor the receiver has actually bent. I just noticed the pealing of the paint which I attributed to superficial stress in the metal resulting from the moment that the WD applies to the receiver. The fact that your bent upward is totally consistent with that.

But the packaging of that draw-tite is even worse than the OEM; let alone the material they used which is also thinner.

Please, keep us posted on any future development
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Old 07-31-2015, 11:32 AM   #49
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One more thing I just observed last night while under the car: if the car is equipped with Adaptive Drive (mine is) the hydraulic pump controlling the rear sway bar is right in front of the area in the rear axle carrier where you would attach the CanAm style reinforcement. I'm not sure there's much room there for a bar...
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Old 07-31-2015, 11:45 AM   #50
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One more thing I just observed last night while under the car: if the car is equipped with Adaptive Drive (mine is) the hydraulic pump controlling the rear sway bar is right in front of the area in the rear axle carrier where you would attach the CanAm style reinforcement. I'm not sure there's much room there for a bar...
When we had our Can Am hitch built/installed on the car they said there was a number of different ways of doing it but they had preferences to a particular design.
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Old 08-04-2015, 04:08 PM   #51
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I called Can-Am and they confirmed that they are attaching the reinforcement to the axle carrier (this could be bolted or welded). I asked about additional noise resulting from this and they said that there were no customers complaining about this.

Is this worth to add such triangular pieces to reinforce the drop to the receiver (found this on MB forum)? Is welding close to other welds on the hitch save, i.e. would this not weaken the existing welds? Maybe I am too dramatic about this...



I will meet the installer on Saturday. I do not know if mounting to the cross member is feasible, but anyway I do not want to test this with my car, so most likely I will go with mounting to the axle carrier as Can-Am solution works on many cars.
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Old 08-05-2015, 03:26 PM   #52
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Well, I am not so happy to report some new developments.

I just got back from a 600 miles trip towing a 21 foot toy hauler weighted at a CAT scale at 7000lbs and a tongue weight of about 750lbs (using the Sherline scale). The trip was from San Diego up to Buttonwillow raceway, near Bakersfield. Driving along the I-5 you go up and down the Tejon pass: nothing extraordinary, but still a climb.

The car (2009 X5 35d) performed amazingly, it is truly a great towing vehicle. Drove the entire time in the 60-65 mph range, holding the steering wheel with one hand, very relaxed, no sway of any sort. Going up the hill, the climb was at 45mph throttling 3rd. Coolant temperature, oil temperature and EGT all stayed very well withing acceptable ranges. Average MPG for the trip right around 12.

The disappointing part is the hitch: the receiver bent up (yes, up... read on) about 1/4 inch. You can notice additional stretch mark on the flanges holding the receiver to the cross tube, as well as longitudinally on the tube and on the welds between the tube and the flanges that attach to the unibody. I examined extensively the unibody and did not notice anything out of the ordinary. As a result the support for the bumper cover that is attached to hitch pushes up on the bumper which now rubs slightly when opening the lower rear gate. Nothing that can be noticed by the untrained eye but all unequivocal signs that there is flex beyond the yield strength of the structure which has now deformed plastically.

The hitch bent up because it is not capable to hold the bending moment introduced by the WDH. Plain and simple. There's simply to many arms that multiply the moment. Perhaps statically is just fine but as you drive around and you transition from a road to a driveway or go over bumps, the moment is simply too much.

The bottom line for me is that I continue to have absolutely no intention of welding anything to the chassis so no more WD towing on the X5...

I conclude that BMW says not to use a WD because they actually do understand very well how it works and they have chosen to design a hitch that is aesthetically pleasing but not capable of cope with the moment introduced by the WD.

I continue to be very skeptical of the reinforcement I see around. Perhaps they work very well and get the job done, but be advised that you're bracing it up to parts of the chassis that were never intended to be loaded the way they will once you use a WD. In other words, I guess I was the first one to prove that the BMW hitch is not capable of dealing with a WD system, I am not going to be the first one to crack spot welds on rear cross members (been there with the Z3).

Too bad, because again, the X5 would be more than capable of towing anything in the 7000 lbs range and probably more...
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Old 08-05-2015, 05:30 PM   #53
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Zetatre - What are you using to monitor Coolant temperature, oil temperature and EGT? I've been tracking with BMWhat/Carly app. A bit clunky and I wish we could pull transmission temp. I've never seen anything alarming on these temps climbing vs. running flat.

The X5 is stellar from a power and handling POV, likely only rivaled by a few. I've done a couple pretty aggressive moves on wide open roads to see what an emergency maneuver would feel like with the trailer in tow an was honestly surprised how well things tracked.

What's your hitch setup? Reese Straitline here with 800lb bars. 600's just didn't feel drive to my liking. Same fender heights and the 800's handle great.

No more flex with my strut brace. Living on the edge. Then again I'm longing to get back into a pickup, but not for these reasons. Towing is one of the times I enjoy the X5 the MOST! Yup, i just said it.
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Old 08-05-2015, 05:55 PM   #54
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Zetatre - What are you using to monitor Coolant temperature, oil temperature and EGT? I've been tracking with BMWhat/Carly app. A bit clunky and I wish we could pull transmission temp. I've never seen anything alarming on these temps climbing vs. running flat.

The X5 is stellar from a power and handling POV, likely only rivaled by a few. I've done a couple pretty aggressive moves on wide open roads to see what an emergency maneuver would feel like with the trailer in tow an was honestly surprised how well things tracked.

What's your hitch setup? Reese Straitline here with 800lb bars. 600's just didn't feel drive to my liking. Same fender heights and the 800's handle great.

No more flex with my strut brace. Living on the edge. Then again I'm longing to get back into a pickup, but not for these reasons. Towing is one of the times I enjoy the X5 the MOST! Yup, i just said it.
I use the same app you used in tandem with the Bluetooth OBD reader they make. It works good to me. I've wrote them many times asking about accessing the transmission oil temperature to no avail... They are stubborn Germans

I have the original BMW hitch kit which is rated 600/6000. There's a bold "DO NOT use Weight Distribution Systems" on both instructions and the rating sticker... I originally subscribed to the theory that it was because "they didn't understand how it works"... It's either coincidence or they do know how it works... Either way it doesn't matter. The point is simple: do not use a WD with the unmodified BMW hitch. If you want to use a WD you need to add a brace of some sort, my original idea of reinforcing the hitch within itself won't be enough.

The WD system is a plain and simple Husky with bars rated at 800-1000. I don't think the WD system makes any difference: the receiver doesn't care how it gets the moment required to transfer load.

Here's a few pictures of the rig:



I truly enjoyed pulling with the X5. It just worked so well on all points but the hitch.

I respect those that decide to add reinforcements, but it's just not for me for all the reason I've been debating with jcl so I've been looking at a 3/4 ton truck. In an attempt not be nostalgic of the X5 I'm looking at a Ram 2500 with the straight 6 Cummins and Laramie Longhorn trim. The GMC 2500 HD Denali are nice too, too bad they are V8s...
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Old 08-05-2015, 06:41 PM   #55
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Got it. Yup, force is force, Just was curious what setup you were using and how it was working out. Of the top of my head I think my fenders ran 31.5" front and rear on level ground as measured at the center of the hub.

Nice short connection there! Well done.
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Old 09-12-2015, 12:52 PM   #56
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A few photos of the reinforcement - BMW X5 E70

I hope this will be strong enough - this is not a big tube as used by Can-Am. I have added two triangles at the both sides of the receiver. I decided also on different attachment. Please let me know what do you think.







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