weight distribution hitch

[hillbillyhotel]

[Padgett]

Back when I was in college on the GI Bill and running a BP Corvette (63 FI Split Window) on no money one of my few advantages was use of an IBM 360 to model suspensions with six degrees of freedom. Had to extend the software from a 3/4 gee max to 1.25 took some programming. Then figuring how a plastic pig aka flexible flyer wanted to move and using that to make it handle took a lot of connect hours.

Like I said, the roll cage was a suspension component and if you could carry the inside front tire 4" off the ground (to clear the bumps) while in a 35 degree drift you could add about five feet to the inside of a turn and surprise the corner workers. I like a car that can oversteer at will.

Today my PCs are much more powerful.

[TrailManorMan]

ZZZZZzzzzzzz

[Mr. Adventure]

Bill's got the right idea with his levers. Wheelbase + the rear axle to hitch ball distance divided by the wheelbase is the lever that loads the rear axle from the hitch ball. For Padgett's vehicle, that means 1.33 times the tongue weight will show up on the rear axle. The total tow vehicle weight after hitching has to remain equal the weight of the unhitched tow vehicle plus the tongue weight. Therefore the front axle will be lifted by whatever excess over the tongue weight applies at the rear axle, in this case .33 times the tongue weight.

However interesting dynamic numbers might be, The doorpost labels, and the owners' manual are where we get the guidelines for applying manufacturers load ratings. The truck scale is where we find reality.

[Mr. Adventure]

Originally Posted by Mr. Adventure

... However interesting dynamic numbers might be, The doorpost labels, and the owners' manual are where we get the guidelines for applying manufacturers load ratings. The truck scale is where we find reality.

Yes, the truck scale gives us the weight numbers in black and white which we need in order to understand where we are relative to manufacturer's ratings and guidelines. And the closer we are to the edge of the envelope, the closer we should be paying attention.

But reality, to Padgett's point, is way more complicated than ratings and guidelines, and the most important realities are on the road, not on truck scales. Using a WDH doesn't automatically make a vehicle safe, just as a 10,000# tow capacity improves some of the variables but doesn't give anybody a free pass to safety. In the end, in all vehicles, the things we do are usually more important to safety than the things we buy.

[LoveToCamp]

What I take away from these mathematicians discussing WDH is, just because my math teacher marked my answers wrong, I may not have been wrong after all! Too many variables.

I have enjoyed this discussion, even though I am not a long-hair when it comes to math. When Bill spoke of levers, I was thinking about springs/suspension, then that was addressed. This discussion has let me better understand the math of WDH, even if I can't replicate it in future discussions. Good to have a better understanding of most topics.

[duvalbirder]

My husband and I are almost TrailManor owners. We have purchased a tow vehicle, a 2015 Jeep Grand Cherokee 4x4. We have having the factory tow package installed tomorrow. We have put a deposit down on a 2007 sl.

And here is my question...do we need a weight distribution hitch? I've gone through all the old emails on this subject, and I am still quite confused. The camper is 4 hours away, so will take that long just getting it home.

[TrailManorMan]

That is an individual thing, I don't use one, others do and other will insist on it!
Many questions and opinions too follow

[Bill]

DuvalBirder -

Welcome to the group!

Once again, here are two answers to the question "Do I need a WDH?"

1. Pack up your camper and your tow vehicle in ready-to-camp condition. Include everything - food, water, propane, tools, clothes, passengers, etc. Find a scale (CAT scales are everywhere www.catscale.com), and weigh the three axles of your camping rig. Look at the weight reading for "Drive Axle" (rear axle of the tow vehicle). Compare it to the Gross Axle Weight Rating - Rear (GAWR-R) for your tow vehicle, which is probably posted on a sticker on the driver's door. If the actual weight exceeds the rating, then YES - you need a WDH. I've shown below an example of the door-post sticker that I pulled off the Internet. It is an example only - it does not represent your Cherokee. But in the example, you can see that the GAWR-R is 3404 pounds when the truck has P225/75R15 tires.

2. Again, pack your camper and your tow vehicle in ready-to-camp condition. Park your car and your TM in line in a level spot, but don't hook them up. Now measure the distance from the ground to some convenient point on the front bumper (mark it with masking tape), and do it again on the rear bumper. Now drop the TM hitch onto the ball. Measure the heights again. The front bumper will have risen, and the rear bumper will have dropped. There are various rules of thumb, but most of them conclude that if you add the rise in the front to the drop in the back, and the sum exceeds about 2 inches, you need a WDH. For your Cherokee, this is primarily driven by the relatively short wheelbase (< 115 inches, same as my much-loved Explorers).

Some of our members choose not to use a WDH despite these tests, and that is their choice. But these are common tests, recommended by tow vehicle and trailer manufacturers, so they do so at their risk. Just to prepare you, the answer for your Cherokee will almost certainly be YES. And by the way, you almost certainly do NOT need a sway control device, though it can't hurt to have one.

By the way, the Factory Tow Package is an option that is built into the vehicle as it is built at the factory. I'm not sure what it means to have the Factory Tow Package installed at some place that is not the factory (such as the dealer?). Be sure you understand what is done as part of this operation.

Bill

[davlin]

Welcome DuvalBirder!

You're going to have a fantastic time with your "new" TM. This is the best place to get rock solid answers to your TM specific questions.

Bill should have included a point #3 about WDH's, although with a 2720 it's probably not a concern, but you should still check.

3. Even if you do not exceed your GAVW-R, and your tow vehicle is acceptably level when connected to your TM, you need a WDH if the tongue weight of your trailer exceeds the maximum "undistributed" capability of your hitch. Said another way, if you had a Ford F550 with the biggest diesel engine that you could get, and 38,000 lbs. of towing capacity, but it came with the same factory hitch as my F150, you would have a 500 lb "undistributed" rating on the hitch. That means if your trailer tongue weight exceeds 500 lbs (all 3124 models, and I think 2922's?) you need a WDH. I couldn't find the factory hitch tongue weight capacity for a Grand Cherokee, but I bet Padgett has it!

Dave