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Old 12-09-2015, 12:23 PM   #1
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GL 450 (or maybe any tow vehicle) long post

Hi,

I'm posting here rather than a Mercedes site because the people here seem to be willing to tow heavy trailers and use WD hitches despite the GL 450's maximum TW of 600 lbs with or without a WD.

My Gl 450 is a 2012 and I have weighed it with and without me in it and with and without a trailer. Also weighed it with the trailer bot with and without the WD engaged. The TW, 720 lbs, was measured with a tongue weight scale.

GL Ratings: the Faxle rating is 3240 and the Raxle is 3968 which total 7208. However, the stated GVWR on the jamb sticker is only 6944. So, first question is why the GVWR is less than the two axle ratings?

The car without me, but with a full tank of gas, weighs 5,550. Faxle 2760 and Raxle 2790. Add my 210 weight and the Faxle increases to 2880 and the Raxle to 2880. So 57% of the front passenger weight goes to the front axle and 43% to the rear axle.

So, I know that my GVWR is 6944 lbs and my actual vehicle weight is 5550 lbs so my cargo capacity (trailer tongue weight and all cargo/passengers) is 1394. Subtract the TW of 600 and I can carry 794 lbs more.

The reality is my actual TW is 720 and I have a WD hitch on which extends 11" beyond the receiver vs the factory stated limit of 7.5". The WD hitch was on but the bars were disengaged for the following weigh in.

The scale indicated a Faxle weight of 2480 (lighter by 400 lbs) and trailer weight of 4500 (lighter by 60 lbs) and a Raxle weight of 4080 (Increased 1200 lbs). This put the Raxle over the rear axle limit with an empty trailer and me!

So, my assumption was that I could take a trailer with a 600 lb tongue weight, drop it on the weight carrying receiver, throw 794 lbs into the car and be good to go. But based on the above test, I couldn't unless the extra 120 lbs of TW and the 3.5" of hitch extension changes the outcome that drastically. Does it? I wouldn't have thought it would have made that much difference.

Also the above weigh in took place twice. Once with the trailer loaded onto the ball after the car was level but with the Airmatic disconnected and once with the Airmatic working. There was no change in the actual weights with or without the Airmatic engaged.

Now using an Equal-I-zer hitch (came with the SOB) I was able to adjust the Faxle back to 2880, the Raxle to 3460 and the trailer to 4680 and I still have room to distribute more. I have to say that getting the spring bars into place without the spring bar tool requires me to almost lift the GL (using the tongue jack) off the ground. That allows me to just swing the arms into place. An option is not raise it as much and use the spring bar tool they provide to lift and snap the bars into place but I am playing around with this to see what works and what doesn't.

So, if you made it this far, thanks for your interest and patience. Any and all thought and advice welcome. First and foremost, I want to tow safely. I like my wife and my two Newfoundlands. Also, the GL. The trailer, not so much. Definitely NOT an AS.

Mark
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Old 12-18-2015, 08:49 PM   #2
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Lightbulb

Hi Mark. Welcome to the forums. The lack of response to your post may be because it is not clear what your question is.

If you are asking whether it is safe to exceed the ratings set by your vehicle manufacturer, the short answer is no. You vehicle ratings are based on what the TV is designed to safely handle. With that said, there are numerous posts on the forums about special set ups from CanAm RV Centre in Canada where people are towing sizable trailers with sedans and minivans.

If you have not already gotten your questions answered, you might want to search the forums using a Google search with Airforums at the beginning of the search terms. It also would help folks answer your questions if you provided more detail about what you wanted to tow, with the GVWR and tongue weight (720#?).

Safe travels!
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Old 12-18-2015, 09:16 PM   #3
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I'd contact can-am and ask them for some advice. The tongue weight limit may be more limited by the hitch strength itself than the vehicle weight capacities.
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Old 12-18-2015, 09:30 PM   #4
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Quote:
Originally Posted by NC Camper View Post

If you are asking whether it is safe to exceed the ratings set by your vehicle manufacturer, the short answer is no. You vehicle ratings are based on what the TV is designed to safely handle.
Unfortunately, that's not the case. The tow rating of many vehicles is set entirely arbitrarily, with trucks frequently receiving an inflated tow rating and vans and passenger vehicles receiving a deflated tow rating.

To give you an example, we have towed a 8000lbs trailer with a vehicle rated to tow 3500lbs for three years - with not a single problem to report.

The numbers to take seriously, in my opinion, are axle ratings and tire ratings.

To elaborate on tow ratings, our current tow vehicle is rated to tow 7600lb with a payload a smidgeon below 1400lbs. If we assume a 15% tongue weight, that would arrive at around 1000lbs - leaving, on paper, just about 400lbs for passengers, luggage and gas.

Meanwhile, our old van had the same payload, but less than half the published tow rating.
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Old 12-18-2015, 11:14 PM   #5
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Weight ratings are only part of a good towing combination. Also of great importance is fully independent suspension on the tow vehicle and trailer, low center of gravity of vehicle and trailer, resistance to side and head winds of vehicle and trailer, tires with little side-to-side movement, excellent brakes, wide engine torque range, as well as a short distance from the tow vehicles rear axle to the hitch ball to minimize sway effects leveraged to the tow vehicles steering axle.

The tow vehicle design, trailer design, and hitch design and setup all play equivalent roles. One lousy component in this group and the whole rig will be lousy, or at least less than it could be.

The Mercedes 450 has excellent towing characteristics, as do Airstreams. That is why many Airstreamers here have used the advice and expertise of Can-Am RV in Ontario (who specialize is this type of setup) to get their rigs hitched up properly and have very stable, safe, and satisfying towing combinations. Even though the weight ratings suggest otherwise.
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Old 12-19-2015, 07:24 AM   #6
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Being a former owner of two GL's. I will put in my two cents worth.

CanAm is known for its ability to reinforce any vehicle's hitch to make up for the lack of said vehicle's hitch. I believe they've even done many M Class conversions successfully. I suspect they're the best at doing what they do.

I towed a Casita 17 with my 2008 diesel with no apparent issues.

And then we moved up to a Flying Cloud 23 FB. Shortly thereafter, we bought a 2010 GL. This is where things get interesting.

We towed the 23 for a little over a year (we live in the hilly Ozarks), and I slowly but surely began to noticed the smoothness of the GL's transmission go from silky smooth to not so smooth shifting of gears.

The transmission and rear end issues are not discussed in regard to the many glowing reports of a conversion such as mentioned!

As you can see, my confidence in the OTHER areas of the GL's ability to properly match up to a larger Airstream, caused us to go to a Suburban 2500.

Obviously, this is just my personal opinion, and I'm sure others will say otherwise.

Good luck in your search!
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Old 12-19-2015, 09:49 AM   #7
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A long term use report

http://maze.airstreamlife.com/catego...ercedes-gl320/
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Old 12-19-2015, 12:16 PM   #8
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HI everyone and thanks for the responses. I really only had two questions when I posted. The information I included was meant for background about what I was doing to figure out what I had (TV, TT and Equal-i-zer hitch) and how to safely use all of it together. Fortunately I have a scale a few miles from my house and I bought a Sherline scale to accurately measure the tongue weight.

So, Question One, was: Is it standard practice across vehicle mfgrs. to have the GVWR rating be less than the sum of the axle ratings? My 2012 Gl450 has a GVWR of 6944 which is 264 pounds less than the two axle ratings (front 3240, rear 3968). These numbers are posted on the sticker on my car.

Question Two was related to my surprise at how overloaded my car was when I exceeded the TW of 600# by 120# and the distance the ball was from the receiver. Mercedes apparently has a 7.5" maximum distance and the Equal-I-zer is 11". I would have expected these differences to be relatively insignificant but together they worked to overload my rear axle and shifted quite a bit of weight from my front axle. My front axel went from 2880 to 2480 and my rear axle went from 2880 to 4080. Did not see that coming. So Question Two was for the towing experts: Any of you surprised at the effect of slightly overloading the tongue and increasing the lever effect? Or are you all just rolling your eyes and thinking, 'Well, duh!'

A new question is whether anybody was surprised that the 4-bag Airmatic system had ZERO effect on weight transfer. It did a great job leveling the GL back to correct height on both axles but did absolutely NOTHING to transfer weight from the rear axle back to the front. Weighed with and without the Airmatic working (pulled the relay). More eye rolling?

I do plan on calling Andy to see if I can send him my hitch rather than driving 8 hours up there but if I have to drive, oh well. Tried half a dozen shops around Chicago and nobody will make any mods.

As far as the weights across the axles, tongue and TT, I don't plan on exceeding the TV or TT but the TW is a question mark depending on how different people interpret TW or 'Tongue load'. My TT dry is 5286 (which includes a measured TW of 720#). Max TT weight is 6500#. MY Gl can tow 7500# but has a TW max of 600# with our without a WD. With the Equal-I-zer I can change the downward force on the ball from 720# to #430. I've read quite a bit on the subject of TW and remain perplexed as to how to interpret my results. I know the TW doesn't go away but the downward force is no longer 720# but now measures 430# with the rest being transferred (via leverage) to the TV front axle and the TT axles. My question, should any one care to weigh in, is this: Since my properly balanced, fully loaded TT wants a TW of 720# (11% of TT) and I now have shifted some of that 720# so that the downward force is only 430# and my TT now weighs somewhat more than 6500#, haven't I disturbed the TT balance? The scales think the TT axles weigh more and the TW (downward force) is less.

I have been doing a TON of reading over the last few months and the TW/Tongue Downward Force issue is still one where confusion remains. I'm thinking Andy's opinion on this subject may prove definitive for me anyway.

Mark 'who is trying to do the safe thing (mostly) and who Really wants an FC' Wall
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Old 12-19-2015, 02:19 PM   #9
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Originally Posted by mwmwall View Post
So, Question One, was: Is it standard practice across vehicle mfgrs. to have the GVWR rating be less than the sum of the axle ratings? My 2012 Gl450 has a GVWR of 6944 which is 264 pounds less than the two axle ratings (front 3240, rear 3968). These numbers are posted on the sticker on my car.

<snip>

A new question is whether anybody was surprised that the 4-bag Airmatic system had ZERO effect on weight transfer. It did a great job leveling the GL back to correct height on both axles but did absolutely NOTHING to transfer weight from the rear axle back to the front. Weighed with and without the Airmatic working (pulled the relay). More eye rolling?
Yes, it is standard practice for the GVWR to be less than the sum of the axle ratings. Pretend you are the vehicle designer. You design the vehicle for a maximum GVWR of 6000 lbs, as an example, considering more items than simply the axle ratings. Now, if you want to use a 3500 lb axle and a 2500 lb axle, which would handle the 6000 lbs, you will need to know exactly where the payload is applied, more to the front or more to the rear. But the real world isnt like that, so you design to cover a range of possibilities, from heavier passengers towards the front to fewer passengers with more cargo right at the rear.

No surprise at all that the air suspension doesn't change weight distribution. It isn't designed to. It is designed to change an effect of improper weight distribution, namely whether the vehicle is level or not.

Jeff
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Old 12-19-2015, 02:55 PM   #10
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Drove my 2007 Mercedes ML320 CDI diesel to CanAm fromPhoenix and back in seven days (4,400 mile round trip). They welded a brace between the recall repaired factory receiver and put the air suspension tank below the brace. I had the stinger to my Hensley hitch with me and they cut off about 5" on the car side and slightly bent it to preload the weight distribution bars.

I arrived in Los Angles to pick our new 2013 25FB International Serenity (GVW of 7,300 pounds). The dealer had installed street side and rear awnings, a 155 watt solar panel and while there the Hensley hitch head. Tongue weight was 1,150 pounds with full propane tanks and fresh water as reported by the Shureline scale. Crossed the CAT scales with just me in the car and all axle weights were below maximum ratings. Towed the steep incline on I-10 east bound out of Palm Springs at 55 mph and it down shifted to fifth and 2,200 rpm and was happy. Passing into Arizona the speed limits went to 75 but I drove 55. I could see them coming up and passing, but the Hensley kept all sway issues at bay.

Returned to the CAT scales loaded for camping with some gear in the back if the car and my wife along. The car axle ratings were exceeded and the tongue weight was now 1,150 pounds with all the toolset interbank of the trailer.

A new 2012 Dodge Ram 2500HD Cummins took over the tow job. When the 25FB was traded for our 2014 31' Classic with 10,000 pound GVW, the truck is the proper size for the job.

Then we acquired a 2015 23D International Serenity (6,000 pounds GVW). Hooked up the same Mercedes with the same Hensley and it is the perfect match of car and trailer with all our gear aboard. We even can add the generator and 30 pound propane tank in the car and still be clear.

I operate on the basis of the axle and tire ratings setting the maximum numbers and drive 55 towing. See 16.5 mpg on the level.
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