Rod B

Hello,

I just purchased a new Travel Trailer. The dry weight is 5600 lb and dry tongue weight is 640 lb. I have an appointment to get the hitch reinforced on Monday (after reading this blog: http://airstreamlife.com/maze/2009/07/13/gl320-report/)

I just wanted to know how many GL owners are towing large loads WITH and WITHOUT the factory hitch modified. NOTE: I have a 2008 GL320 CDI and I have had the factory recall completed. I'm assuming I'll be around 6500 - 7000 lb loaded, and I'm not sure what my tongue weight will be in the end, but I will measure it to be sure.

There are lots of posts of people towing big loads, but only one person that I can tell (linked above) has mentioned anything about doing additional reinforcement of the hitch. If you tow, could you please help me out with the following questions?

1. Total trailer weight
2. Tongue weight
3. Factory recall completed? yes / no / NA
4. Additional welding completed? (if so, please describe, if possible. and let me know if you had a failure that prompted the modification)
5. using a weight distribution hitch?

Thanks very much!

Best Regards,
Rod

emayer

Great questions thanks for posting. I believe the blog author is the same person appearing in this month's Star magazine.

One question also: Does the use of a weight distributing hitch help off-load some of the tongue weight? If so, this may permit towing to full capacity without having to further support the hitch receiver. Could really use some help from towing gurus on this one.

Thanks!

IridiumRoad

@emayer: A weight-distributing hitch is pretty much mandatory if you hope to get anywhere near the 7,500 # tow rating of the GL. But there's a big "catch" involved.

First, a little background. Generally, North American towing gurus recommend loading a trailer so that 10-12% of the trailer weight is on the tow ball. This is also sometimes called "tongue weight".

Like some other automotive manufacturers, Mercedes does not comment in the GL owner's manual about the use (or even existence) of weight distributing hitches, despite the fact that they are commonly used in the US and recommended by trailer manufacturers.

But you'll need a weight distributing hitch if you tow a trailer with more than a few hundred pounds of tongue weight, to balance the load. Otherwise, you're putting hundreds of pounds of weight at the very rear of the car (behind the rear axle). The rear axle will act as a fulcrum, and the front axle will get lighter. This can cause very poor handling.

Note that the car may look fine even with a very heavy load on the receiver hitch, but that's because the Airmatic suspension will level up the car even with a ridiculous load in the back. Don't be fooled. If the steering feels lighter than usual, or the car is understeering, or if you experience torque steer when pulling away from a stop, you've been warned by the car that it is not happy with the load.

Now, the problem: The Mercedes factory receiver on the GL is rated for 7500 # of trailer weight, but also has a placarded limit of 600# tongue weight. You can't do that and stay within the generally accepted recommendations of 10-12% tongue weight: Max load of 7500 x 10% = 750 lbs tongue weight. Or, 7500 x 12% = 900 lbs tongue weight.

That means that carrying the full 7,500 pounds requires you to exceed the 600# tongue weight limit. (Mercedes apparently designed the hitch for 8% tongue weight.)

If you overload the receiver, it will break eventually, and you won't get sympathy from your dealer. (I've heard from several people already that this has happened to.) Worse, a receiver break while towing can be catastrophic and even deadly. So, what to do?

Option #1: Reinforce the hitch's weakest spots and try to distribute the load better across the car's frame. You're on your own here. This is user engineering.

Option #2: Don't tow anything that exceeds Mercedes' recommendations.

There is no Option #3. It would be nice if there was a third-party replacement hitch that is better than the OEM design, but there isn't.

So, to answer your questions, now that you understand the fundamentals:

No, not in the way you mean. The weight is still there. A weight distributing hitch shifts some of the tongue weight to the front axle of the vehicle, thus giving the vehicle a more even load and better handling.

A weight distributing hitch actually puts more stress on the receiver, because it uses that receiver as a lever (with the rear axle as the fulcrum) to shift weight forward. The added stress increases the likelihood of a receiver failure if overloaded.

Hope that helps ...

emayer

IridiumRoad:

On behalf of all readers, thank you very much for taking the time to provide such a detailed and comprehensible explanation.

Too bad must of us with loads greater than 6000 lbs are increasingly being limited to 1/4 and 1/2 ton trucks as most SUV manufacturers are focusing more on fuel economy and a "car like" ride. Compromises have to be made to achieve this, therefore it looks like we're losing some of the U in SUVs!

Best regards

StevethePilot

Ditto.

What do you think about the guy on YouTube who's towing the Airstream? I checked the specs and he's at the top end of the ratings (loaded, not dry, if I'm not mistaken). You're letting us know he's probably looking at a failure, if I read you correctly?

Thanks very much for the very good information!

STP

IridiumRoad

Without reinforcement of the hitch, yes, "the guy on YouTube" would likely have a receiver failure as a result of exceeding the 600# rating on the hitch. Fortunately, he has reinforced his hitch.

mdadgar

You're talking apples and oranges here, IMHO.

The problem with the GL is not the design of the vehicle, it's the crappy hitch they put on it.

You can easily build a monocoque SUV that can handle 8000 lbs and 1000 lbs of tongue weight without compromising the ride, handling, or mileage. You just need to pay attention to the details and in this case, MBZ apparently did not.

- Mark

emayer

Point well taken. With cost not being an object, no question such a solution can be designed though it is likely the MB design/marketing folks didn't see much of a worlwide demand. At this time, the trend amongst SUVs is lighter, more fuel efficient, and compliant at the expense of off-road and towing functionality.

The best example I can think of is the upcoming Ford Explorer. What was once a benchmark truck-based SUV will now be based on the current Taurus platform and will have reduced towing capability also. I'm sure it'll be a greatly improved SUV in regards to drive dyanmics, but some of its former capabilities will be lost.

For those towing larger loads looking for a non-pickup based solution it looks like the Suburban/ Tahoe variants are the only game left in town. I'm using an Avalanche presently myself but would prefer to steal the wife's GL....

mdadgar

Generally agreed, although with the GL I think the vehicle is plenty capable. The problem is with the hitch.

Hey, I tow with an Escalade. I'd MUCH rather have a GL350, but I'll be right, uhh, near the limit (read: well over the hitch limit and just over the gross weight limit with a weight distributing hitch), so I'm moving slowly.

- Mark

emayer

Towing about 7000 lbs myself. From a power and braking perspective I suspect the GL550 would crush the Avalanche if only.....

Mark, keep us posted if you decide to give the GL350 a go. If you haven't already, check this month's Star magazine which gives some great insight. Poking around other posts here, I've seen some others hauling pretty large loads. One has to wonder how they've held up.

One last thought. It may be worthwhile to actually measure tongue weight rather than basing on percentage. Some lucky few may wind up OK.

Good luck!

Eric

Rod B

Well, I just got back from our maiden voyage towing our 30' (34' bumper to hitch) Everlite trailer (5700 lb/640 lb hitch dry weight), and the GL320 towed like a champ!

I ended up going with some significant hitch reinforcement after talking on the phone to Andrew Thompson at CanAm RV (thanks very much for taking the time Andrew!). I will try to post up some pictures if i get a chance, but we reinforced the main drop to the cross tube as well as doing a tank bar under the air tank that was bolted to the suspension cross member.

With a full tank of water (about 350 lb) all our camping gear I weighed in at 7100 lb. We were within 30 kg of the rear axle max and well below the front axle rating, this was with my wife and four kids in the back and me driving chauffeur. We moved one of us up to the front to even things out, but I didn't get a chance to weigh with the changes. Dry hitch weight was verifyed at 640 lb, I haven't verified my wet hitch weight, but based on my axle weights and the weights of all passengers I think its pretty close (I had weighed the GL with just me in it prior to doing the trailer weights). I am surrounded by hills where I am so I'll try to get a wet hitch weight the next time we go out.

The GL is definitely NOT down on power, I always felt that it had plenty to do the job. We also hit some pretty big cross winds and although I could certainly feel the trailer (mostly when other vehicles passed), I never had to fight the steering wheel. I kept the speed mostly at 110 kph (68 mph) on divided highway and got 12.9 MPG based on the computer. I noticed that I was able to get better milage on roads with a lower speed limit (100 kph / 60 mph), but felt better keeping to the speed limit to avoid the passing (and rocks, etc) from the semi's.

BTW, I believe that someone mentioned above that MB does not explicitly recommend a weight distribution hitch, but that does not appear to be the case in my owners manual. It clearly recommends a "sway control system" with trailers (I have a 2008 Canadian spec GL320), with the following wording: "You should consider using a trailer sway control system. For further information contact an authorized Mercedes-Benz Light Truck Center."

Unless a "trailer sway control system" is different than my weight distribution hitch??

So, to answer my own questions above:
1. Total trailer weight: 7100 lb with gear and full fresh water, 6750 lb with gear, no water.
2. Tongue weight: 645 lb dry (need to verify wet weight)
3. Factory recall completed? yes
4. Additional welding completed? yes, drop reinforced to tube on each side and tank bar installed under air tank. Dropped air tank between 1.5" and 2" with "nut coupler's". Nut couplers/washers are around 1 inch long 'nuts' that are installed on the factory bolts holding the air tank in place, lower just enough to give clearance for the air tank to tank bar.
5. using a weight distribution hitch? Yes, using Reese distribution hitch with 800 lb bars with two loose links. Hitch height is the standard 21.5" to top of ball.

Still hoping to hear more info from other's who have towed, but I'm certainly a happy camper...

Rod B

BTW, forgot to mention that I'm using a Prodigy RF break controller and my trailer has LED tail lights, I installed some 180 ohm resistors (between the Prodigy RF and the trailer) to get the trailer lights to work (that's all I had laying around, and they worked!).

Also, when MB did a recall last November they reprogrammed my SAM and it turned OFF my trailer, so I had NO lights! I had to take it back to the dealer to get the SAM reprogrammed, which was a real PITA!!

IridiumRoad

Glad to hear you got it worked out. Andy T at Can-Am is quite a wizard when it comes to towing challenges.

Yes, sway control is often integrated into weight distribution hitches, but it is not the same thing. You can get sway control with a simple brake-like device and not have weight distribution. MB doesn't talk about weight distribution, but for heavy loads like yours, it is essential.

EWT

Please do post pics when you get a chance. I just picked up an 08 550, and I'm going to use it to tow a boat that weighs about the same as your travel trailer. I saw some pictures of the CanAm modifications somewhere, but cannot find them again. Glad to hear it tows that heavy of a load well.

emayer

Rod B-

Congratulations on a successful conversion and tow! Please post those pics (with trailer attached also if possible ) when you have a chance and thanks for the details given. Do you have a tongue weight scale or how was this measured? Who did the reinforcement for you? Did you come across a solution for extending the side mirrors?

I have to say you guys are really tempting me to start using the GL for towing myself...

BETO

I have plenty of experience towing with Mercedes SUV's, been towing since 04 my trailer with a loaded racecar since there isn't much space in the rear of a ML500, and also to prevent more "loading" on the rear suspension. I have towed the same trailer and equipement with the GL320, and it was much better, a breeze, a walk in the park. However, I got me a full size crew cab diesel pick up because I was tired of "calculating" my towing load. If you want an SUV to tow get a Nissan Armada with a 9,000lbs towing capacity and 900lbs tongue weight.
I towed around 6,500lbs without any issues, no extra welding, no tongue weight distribution, just a trailer brake controller. Besides the GL has an electronic air suspension and towing controller system installed so your SUV won't "wiggle" when towing preventing the trailer to become unstable.
In my own personal experience I will never get an SUV to tow again, unless is just a jetski or a quad, anything bigger than that is a pain, get a full size pick up, Dodge has the same engine and technology, even the speedometer/tachometer look alike, I don't miss my GL320 at all.

emayer

I'm presently using an Avalanche to tow an enclosed trailer with track car, some 7300 lbs total. Interestingly, the hitch receiver on this vehicle is rated for 600lb tongue weight or up to 1500lb if a weight distribution hitch is used. It works fine, but I'd rather be driving something more enjoyable the rest of the time when a daily driver or snow vehicle is called for!

If tongue weight were not an issue for the GL, what is it you didn't like about the SUV for towing?

Rod B

Here are the pictures of what we did. Take a look under your GL and you'll see the differences right away. The GL is high enough that you can take a look pretty easily, if you haven't already. Just remember that the GL automatically adjusts the height so don't open any doors (or even unlock anything) when you are taking a peak. And certainly don't go under there if you've had problems with your suspension sagging, not maintaining it's level. Sorry about the dirty under carriage in the pics! My trailer storage spot is just off a terrible dirt road and it was pouring the last time I dropped it off. All these pictures were taken with the GL on the ground (although I did use a wide angle lens).

Of note:
1. The triangular pieces (most visible in first two images) were added/welded on to re-enforce the drop to the main bar.

2. You can see where the air tank (and pan) were dropped to allow for a bar to be added that connects further forward. A colar nut was added (this is a metric size, a bit hard to find). What I did: thread one regular nut onto the existing MB studs, these can be adjusted up and down as desired. Next a lock washer and the colar nut is installed (be sure to leave enough threads on the MB stud for a solid connection). Next the MB bracket which is held on with a new bolt and flat washer/lock washer combo. You will loose a bit of ground clearance. I did all this myself to save the welder some time on simple stuff. Be careful with the tank air tube, it is just plastic. NOTE: If you have a 2009 or newer, you will have an adblue tank, not an air tank, and will have to route the bar BELOW this tank (see the blog linked in the first post there's a picture of this posted in one of the comments).

3. You can see where the tank bar is bolted on to the suspension cross member (new holes drilled for this).

4. After all is said and done, make sure there is no contact between the newly added tank bar and the air tank (I left enough room to slide a piece of cardboard through). If there is any contact, you'll risk a hole/damage to your air tank.


I've towed at least 1000 KM with this setup so far and no problems yet.

P.S. Credit should go to Andrew Thompson at CanAm RV for telling me about this method of re-enforcing the GL hitch.

EWT

Since my newly acquired GL550 will occasionally be towing a ~7000 lbs. boat, I decided to get my hitch reinforced before installation. I only went with the additional gussets between the drop down section and the main bar since I'm not going to be towing on a regular basis, and as shown in the pictures, the hitch should now be substantially stronger than it was in stock form. I first approached a local hitch place, but they declined to do the work for liability reasons. I ended up having the work done at a local truck repair shop, and they did an outstanding job IMO. Very nice welds, and they even painted it for me. It looks like it was built that way from the beginning (and probably should have been). The supervisor told me the rest of the hitch would break before the drop down part came loose, and I suspect he's probably right. Here's some pictures of what was done.

Rod B

EWT,
They did nice work on the welds.

I should also mention that I initially took my hitch in and got the additional gussets done. Initially I had emailed pictures of the tank bar to the welder (from the GL blog in my first post) and they were going to do a tank bar and gussets. When I got there and they inspected it they were unsure about attaching anything to the suspension cross member so we decided to just do the gussets. I had brought my laptop in with me, as I planned on waiting while they did the work. So, in the meantime, I searched the internet (mainly the Airstream forums) for more information on whether the gussets would be enough. I came across the information about Andrew T at CanRV and noticed that he'd helped a couple of other GL owners. I decided to give him a call and see what he thought. He was very helpful and explained exactly what he recommended in addition to the gussets. The welder was there when I was talking to Andrew and he got all the details.

In that conversation, I asked him if he'd seen failures to hitches with JUST the gussets done. Unfortunately, he said yes he had. I didn't ask the details on how big a load, but I made an appointment to take my GL in the next day to get it done. Andrew mentioned that to truly strengthen the hitch you really need to spread out the load to additional points on the vehicle, and the gussets alone do not do that. BTW, the place that did my work was "The Welding Shop" in Calgary, and they are very good. My impression is that they won't do anything to your vehicle that they wouldn't do to their own, which is exactly what I look for.

Of course, I could be paranoid, but for the additional $100 or so, adding the tank bar was good piece of mind, for me at least. YMMV

Cheers,
Rod

EWT

Rod,

Thanks for the information. I don't think I'm going to go with the additional brace once the hitch is on the car. I'm not planning to tow very often, and while I understand the benefit of spreading the load out to another point, I'm not crazy about making a rigid connection between the bumper beam/hitch and the suspension pickup point for the lower control arms. With the amount of towing I'm likely to do, I probably didn't even really need the gussets, but it seemed like cheap insurance since the hitch wasn't even on the car yet. Like you said, YMMV, and hopefully the hitch will be adequate as is.

Eric

Texas993

Reporting in on my recent and first towing experience. 2010 GL350 Bluetec.

I towed a 4500 -5000 lb trailer, 5 family members, and all of our gear for a two week vacation to Colorado. We traveled 850 miles each way from Dallas to Aspen CO.

My only other tow vehicle was a 2007 Cadillac Escalade.

My impressions towing with the GL350:

• Plenty of pulling power from a stop. Easily maintained freeway speeds of 65-75 mph with no drama, even in windy conditions.
• GL allowed me to use my cruise control without any gear searching (Escalade constantly shifted with the cruise control - couldn't use it).
• While the GL was stong pulling up to 60 mph, it didn't have much power to pass, etc at speeds above that. Not really an issue, but passing on 2 lane highways took a lot of patience.
• Mileage was respectable. See pic. I averaged 15.7 mpg over 840 miles of mountain passes in CO, head winds in West Texas, and moderate flat highways. (My Escalade averaged 9 mpg on premium.)
• As others have stated, the exterior mirrors are small.
• I like the fact that the rear camera allowed me to see my hitch for the times that I was connecting the trailer.
• Riding in the fully loaded vehicle with trailer attached was not much different that without the trailer. In other words, didn't bounce over bumps, shutter, etc. Very comfortable.
• The diesel was a beast when climbing up steep mountain passes at slow speeds. The engine stayed cool and just pulled and pulled. Nice! (Anyone ever driven up Independence Pass, CO?)

My overall impressions were very positive. This is a great vehicle!

EWT

Texas - thanks for the report. Nice looking setup. What were you doing with the 993 on your trip?

Texas993

Driving it! I take the 993 (a RUF Turbo R) with me on vacation to drive it. I put about 1,000 miles on it over 2 weeks. What a blast!

rabtech

I have both a 2010 gl550 and a 2010 ml550. I can tell you both have no problem pulling a 7x20 v-nosed enclosed trailer well into the triple digits. No sway, easy stopping, and this is with it loaded with 6000 pounds of BOSS HOSS v8 motorcycles.

I havent had any re welding done and I haven't had any paperwork recalling either vehicle.

I attached a pic of the trailer i am pulling. I haven't taken any pics of it hooked up. This is the actual trailer though. I cant believe i still have the pics the salesman sent me of it over a year ago...