Jeep Grand Cherokee and towing

[MrUKToad]

On our Sienna, Andy welded two three foot long sections of 'angle bar' behind the reciever box on the hitch and they bolt to the unibody, or maybe the rear sub-frame, at a point close to the rear axle. This modification does help with the transfer of weight but also provides some strength and rigidity to the hitch to counter the torque that the weight distribution system places upon it. We tow a 28' International with a (real) tongue weight of around 1000lbs so it's important get as much of that distributed to the axles as possible. It works, by the way, and we have a very capable tow vehicle.

[KYAirstream]

So if I understand correctly, the receiver is bolted to the vehicle at the factory mounts, and then these additional bars fasten further up the frame. How much does this affect ground clearance? Any pics available?

[MrUKToad]

KY,

A couple of photos

1. The hitch, quite low to the ground but that's standard:





2. The welding behind the box




3. The added steel in full:




4. The bolting point.





As you say, the unmodified hitch is fitted to the car using bolts on plates at either end of the main tube. Andy's addition is the welding is behind the receiver box and the bars, two of them (one hidden in the pics). They run down the car as you can see. The mod doesn't affect ground clearance but the unmodified hitch is pretty low anyway and the end plates do ground (when not hitched) when going down short, sharp drops, like coming out of gas stations!

[Jim Flower]

The modification on the Jeep runs up beside the spare tire compartment so is not an impediment to Jeep's great ground clearance. Since the modifications are vehicle specific, the clearances and the impact on performance obviously will vary. The 28' airstream is not a feather weight, so MrUKToads towing performance is impressive.

[Road Ruler]

Originally Posted by KYAirstream

So if I understand correctly, the receiver is bolted to the vehicle at the factory mounts, and then these additional bars fasten further up the frame.

Years ago my dad had an RV sales business and had a local welder custom build receivers. They were massive and spread across a wide area in the back of the vehicle. They worked great. Today modern receivers are by design, not that good.

Today, more or less, many/most receivers flex. Flex absorbs the weight that the WDH is trying to transfer to the front axles. The reinforcements curtail the energy lose. This applies to unibody's and full framed vehicles.

[KYAirstream]

Thanks for the pics. Do you recall the size of the angle supports? 2" square?


I see that while the receiver is quite wide, that the angle supports are pretty close to each other, being on both sides of the receiver box. I suppose where the angle supports are placed largely depends on where they can be bolted to the vehicle, as well as where they can be welded to the receiver. Seems any additional attachment at all would help tremendously. Great setup, and those pics really help to explain. Thanks.

[KYAirstream]

Originally Posted by Road Ruler

Years ago my dad had an RV sales business and had a local welder custom build receivers. They were massive and spread across a wide area in the back of the vehicle. They worked great. Today modern receivers are by design, not that good.

Today, more or less, many/most receivers flex. Flex absorbs the weight that the WDH is trying to transfer to the front axles. The reinforcements curtail the energy lose. This applies to unibody's and full framed vehicles.

Good point about the flex mitigating the effect of the WDH.

[rodsterinfl]

I understand that it is possible to weld metal to a frame to reinforce a vehicle and, that people do that for a living and certainly know more about it than me; however, there are certain rules of physics that just should not be overlooked just because a trailer can be pulled. I have a "years ago" story too. My family were/are car people - all from that industry for the most part. Years ago when vehicles had full frames and heft, cars towed much more than they do now. It is not only the weight but build quality and materials that contribute to the situation. One thing my father (big-time boat towing guy) said is that a vehicle can pull anything that is no more than its own weight. I guess that used to be the general rule. The WD hitch allows for some beyond-that figuring but my concern is that people will tend to overload. The GC overland weighs about 4700 lbs in 2wd form. That with its short wheelbase make it more susceptible to sway, etc. with the heavier longer trailers mentioned here.Again, there are people that will tow anything as long as the hitch fits and it will roll and while you can beef up a vehicle to tow something better, I would not recommend towing something 2000+ lbs heavier than its maximum recommended weight on a regular basis or for a rig setup. Correcting for lower payload and all factors is a challenge. After reading the posts and thinking about your question, I would go for the Expedition. That way you get super payload and towing ability in a large SUV and it does not require alteration.

[Andrew T]

Hi Rod

It is easy to assume that because of their size cars of old were heftier or better tow vehicles but nothing could be further from the truth. Modern cars are dramatically stronger with much better suspension steering and general layout for towing. In any vehicle other than a pick up the real strength comes from the body not the frame. Watch the box on your Pick up in the mirror on a rough road and you can see how much your chassis flexes.

The Grand Cherokee's short wheelbase is helped by its short overhang we look at the overhang as a percentage of wheelbase, that is much better measurement to look at than wheelbase alone.

The current generation Grand has a longer wheel base and independent rear suspension so it is dramatically more stable than the older ones but with a Hensley any handling issues on the older Jeep's are pretty much eliminated. A Hensley actually works better on a shorter vehicle than it does on a longer one because of where it projects the pivot point to.

The weight of the tow vehicle really has very little to do with its handling capability. The two fastest vehicles towing a 34' Airstream in our Slalom and Lane Change tests have been a Jaguar XJ weighing 3800 pounds and Chrysler Intrepid weighing 3600. The slowest is a 7000 pound Deisel truck. Obviously the diesel truck has a primative suspension compared to the Jag so it is not a back to back test of weight alone which is hard to do as it is pretty hard to find two identical tow vehicles that have different weights. It does point out that there is a lot more to control than the weight of the tow vehicle.

If I wanted a traditional large SUV the Expedition would be high on my list because of it's independent rear suspension. In fact we recomend it regularly for trailers that have a lot of air drag. It needs its hitch reinforced just as much as the Jeep does.

Here is a picture of a GM Truck hitch Reinforce which is similar to the Jeep.

[c_lewis77]

How would the drivetrain on the jeep grand cherokee handle the extra weight if it outside the recomended tow limits? Does that void the mfg warranty if you have any issues?
I tow with a v10 excursion and it works for me for many reasons other than tow capacity. I recently had to tear down and completely overhaul the transmission...it was interesting to see the wear and tear on a HD tranny. I am not knocking the smaller vehicles, i find andys work very knowledgeable and insightful, just do your homework before you hook up and be safe!
Btw, nice work on the jag andy! I had an old xj series iii, great car to drive!

[Road Ruler]

Originally Posted by c_lewis77

How would the drivetrain on the jeep grand cherokee handle the extra weight if it outside the recomended tow limits?
I tow with a v10 excursion ... I recently had to tear down and completely overhaul the transmission...

A good topic.

My take..... An Ex towing at it's max rating and being over 10 years old probably reached it's tranny life expectancy.???

Some vehicles have marginal tranny's while others seem to have overbuilt trannys. Research needs to be done to see what ones are good for towing.

Our Nissan van had an overbuilt tranny which came from the Infiniti Q45 (V8). No problems towing for 10 years and over 300,000miles on the od.

Our V6 car has the same tranny used in the Infiniti FX45 SUV, with a V8.

Both our car and van had lower HP engines when compared to the V8 vehicles the tranny's were made for. For us with lower V6 power pushing on the V8 built tranny's it is a bonus. Not enough power to hurt them.

The G35 is now 10 years old with 200hrs of towing the 23'. Tranny works as new.

As for the Jeeps??? Reseach should tell you how good it is.

[Denis4x4]

Originally Posted by c_lewis77

How would the drivetrain on the jeep grand cherokee handle the extra weight if it outside the recomended tow limits? Does that void the mfg warranty if you have any issues?

First off, if someone is stupid enough to exceed the tow limits (4x2=7400# or 4X4=7200#) then a dealer is within his rights to refuse to honor the warranty. It's interesting to note that the warranty and/or the owner handbook doesn't say "80% of the towing capacity" is the correct trailer weight.

One could extrapolate that the real towing capacity of a Grand Cherokee 4x4 with the tow package and hemi is 8640 lbs. based on the Airstream Forum rule of "not exceeding 80%"!

[MrUKToad]

Originally Posted by Denis4x4

First off, if someone is stupid enough to exceed the tow limits (4x2=7400# or 4X4=7200#) then a dealer is within his rights to refuse to honor the warranty. It's interesting to note that the warranty and/or the owner handbook doesn't say "80% of the towing capacity" is the correct trailer weight.

One could extrapolate that the real towing capacity of a Grand Cherokee 4x4 with the tow package and hemi is 8640 lbs. based on the Airstream Forum rule of "not exceeding 80%"!

I think it's short sighted to reduce towing capability to a simple measure of weight, as manufacturers do. As we all know, weight is only one element of towing; it's important but not as important as wind resistance and the resulting drag. A flat fronted 4000 lb SOB being towed at 60 mph is going to make an engine and transmission work so much harder than a reasonably aerodynamic 6000 lb Airstream being towed at the same speed. It doesn't follow, then, that a heavy Airstream will cause transmission problems before a lighter but less aerodynamic SOB. That a manufacturer might attempt to wriggle out of a warranty claim based on the over-simplified tow rating is another issue, of course.

[SteveH]

A tow vehicle doesn't give a tinker's damn about wind resistance when it's towing 8000 pounds up a 8% grade at 10,000 ft AMSL at 30 MPH, all it see is the grade and the additional 8000 pounds.

That's what manufacturer's tow ratings are about, not about going thru a slalom course.

[Road Ruler]

Originally Posted by SteveH

A tow vehicle doesn't give a tinker's damn about wind resistance when it's towing 8000 pounds up a 8% grade at 10,000 ft AMSL at 30 MPH, all it see is the grade and the additional 8000 pounds.

Wrong!

I am an avid bike (with pedals) rider/racer and have gone 30 MPH*. I can tell you that the wind resistance at that speed is substantial. The Airstream does have an aerodynamic advantage going up hill at 30MPH. If you also have an aerodynamic TV the advantage is even higher.

*Once on a down hill I hit 51MPH. Funny thing was my BH was right behind me on her bike. The tires were up to the task. We don't use ST tires on our bikes!

[SteveH]

And you've done that on a bicycle towing an Airstream and then later a SOB to measure the difference???


And, spoken by someone from a province with the tallest "peak" of a whopping 1030 feet rise above surounding terrain.

[Road Ruler]

Originally Posted by steveh

and you've done that on a bicycle towing an airstream and then later a sob to measure the difference???

LoL!

[MrUKToad]

Originally Posted by SteveH

A tow vehicle doesn't give a tinker's damn about wind resistance when it's towing 8000 pounds up a 8% grade at 10,000 ft AMSL at 30 MPH, all it see is the grade and the additional 8000 pounds.

That's what manufacturer's tow ratings are about, not about going thru a slalom course.

You're right, the slower the speed the less important the drag and the more significant the weight. But how often are you towing up grades like that and going at 30mph?

Try clocking your gas mileage on the level for a few hours into a headwind and compare it to your usual consumption, then you'll see the effect of wind resistance.

Most tow ratings are not worth the paper they're written on; they're not much more than marketing tools and bear little or no relation to the actual towing capability. As I said before, you can't quantify towing into a simple measure of weight, there are just too many variables.

[Bob4x4]

Something I haven't seen brought up here is the stability controls that have been added on the new models. They will make the combination handle much safer than the. Tv's of yesteryear

[slowmover]

Aero resistance means more than weight. The "tow ratings" all have frontal area restrictions which limit weights. Were they an honest assessment they would also include length and sidewall height. They don't . . and thus aero trailers slip through the cracks of what is possible according to general common sense. Ignorance of what is possible. Nothing new here, it's been understood with some thoroughness since the 1930's . . just forgotten or ignored. Drowned under TV ads and the like.

And, if the majority of cars, etc, are never tested -- just given a generic "rating" -- that then serves the profit dished up by pickups to the OEM's.

An Airstream and it's cousins is a TT designed to be towed by automobiles. Putting a poor performing truck-based TV in front of one is rather bass-ackward, in main.