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Old 07-05-2016, 05:54 PM
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WDH vs GAWR

I have a question regarding the use of a weight distributing hitch in the context of our vehicles gross axle weight ratings.

As I understand it, a WDH will move weight off of the back axle of the tow vehicle and split it between the front axle and TV axle(s). Standard operating procedure with a QL system appears to be to setup the WDH with QL off and adjust until the tire differential between the front and back (measured from the ground to the wheel well) is the same loaded vs unloaded. Then you are basically done.

However, when looking at the GAWR it looks like the front axle has an appreciably lower rating than the rear at 3200 vs 3600lbs. Furthermore, the weight distribution of Jeep itself is such that it is already front heavy with a CAT measured the unloaded curb weight on the front axle is 2840lbs vs 2440lbs - which is consistent with the published specifications.

Wouldn't this mean I should try keep the weight biased towards the back end instead of "even", given that when unloaded the jeep only has ~400 extra pounds to give on the front axle vs ~1200lbs on the back? Considering Jeep recommends using a WDH for loads over 3500lbs I realize I may not be thinking about it quite right, but would like to understand whats going on . I am having a new hitch setup on Thursday and want to make sure it's done right so any help would be appreciated.

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Old 07-05-2016, 08:37 PM
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Re: WDH vs GAWR

Setting up a WDH isn't necessarily going to give you "exact" amounts of weight shift. The idea is to get things back toward "normal" balance between front and rear rather than loading the back. That keeps stability, steering and braking as effective and efficient as possible. So as long as your WDH is adjusted with that in mind, you'll be fine.
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Old 07-05-2016, 09:48 PM
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Re: WDH vs GAWR

Quote:
Originally Posted by Jim_in_PA View Post
Setting up a WDH isn't necessarily going to give you "exact" amounts of weight shift. The idea is to get things back toward "normal" balance between front and rear rather than loading the back. That keeps stability, steering and braking as effective and efficient as possible. So as long as your WDH is adjusted with that in mind, you'll be fine.
Hey Jim - thanks for the quick response. Wouldn't you run the risk of overloading the front axle weight limit though if you took that approach, since it has a lot less overhead when unloaded?
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Old 07-06-2016, 09:13 AM
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Re: WDH vs GAWR

You're only spreading a couple hundred pounds...dividing the tongue weight, as it were, not the total weight of the trailer... But those hundreds of pounds do make a difference in handling. My small horse trailer with both beasts aboard comes out at about 5200 lbs and without WDH, the imbalance is very noticeable, even though the vehicle is perfectly level, because of that tongue weight being well above 350 lbs. The specific trailer characteristics and how it's loaded will affect how much compensation is needed from the WDH, but again, you really can only approximate things. Knowing what the loaded tongue weight of the trailer is is very helpful, however, for getting the adjustments at or near the sweet spot as well as for choosing the "correct" WHD for the combination.
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Old 07-06-2016, 12:15 PM
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Re: WDH vs GAWR

Quote:
Originally Posted by Jim_in_PA View Post
You're only spreading a couple hundred pounds...dividing the tongue weight, as it were, not the total weight of the trailer... But those hundreds of pounds do make a difference in handling. My small horse trailer with both beasts aboard comes out at about 5200 lbs and without WDH, the imbalance is very noticeable, even though the vehicle is perfectly level, because of that tongue weight being well above 350 lbs. The specific trailer characteristics and how it's loaded will affect how much compensation is needed from the WDH, but again, you really can only approximate things. Knowing what the loaded tongue weight of the trailer is is very helpful, however, for getting the adjustments at or near the sweet spot as well as for choosing the "correct" WHD for the combination.
Understood. I guess I don't understand then why there is so much more overhead on the rear axle weight rating if they recommend sharing heavier loads between axles, unless the sharing is intended to not be uniform only for the heaviest of loading conditions (but balanced is preferred for the best handling)?
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Old 07-06-2016, 12:41 PM
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Re: WDH vs GAWR

Jim has it right..

The rear GAWR is designed to be higher due additional/variable load(s) placed on the rear of your JGC. They include fuel load, load in the luggage area, rear passengers, tow hitch weight etc.

A WDH will shift some of this forward, thusly distributing the GVWR somewhat more evenly.

Getting your towing set-up right given the differing weights both inside and on the TV and Trailer, variable towing weights, proper distribution etc is somewhat of a "black art" but you'll eventually come to the correct set-up. Just be careful not to exceed the actual JGC payload number. One thing that would help is to shift any load in the back of your JGC into the rear of your trailer. This moves the CG rearward on your trailer and anything you can put in the rear of your trailer would help.

I'm also a pilot and we HAVE to deal with CG (Center of Gravity). However, each aircraft has a fixed set of location ID's and 'moments' allowing us to keep the load within safe and approved limits. This is why, IMHO, it is important to load your TV and TT and ensure all weights (and heights) involved are within safe limits. Taking your road ready/loaded TV/TT combo to a CAT scale will give you an excellent idea of all axle loadings. You can then take your unloaded JGC to a CAT scale and then do the math to get the exact weights.
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Old 07-06-2016, 12:47 PM
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Re: WDH vs GAWR

It's not about load...it's about balance. If you put too much weight on the back, it effectively makes the front "lighter" with less contact on the road and that brings a resultant reduction in steering, braking and stability. When your tongue weight gets substantially above 350 lbs (there's a 720 lb max), things start to get "squirrelly" and uncomfortable. This isn't a JGC thing...it applies to any vehicle used for towing and it comes from how levers work from a physics perspective. Think of the teeter-totter in a playground. With the "balance point" in the middle two kids of equal weight/mass can easily lift each other as the ride moves up and down on alternate ends. If you put a kid on one side and an adult on the other, that balance point doesn't work because the "kid side" no longer has the same level of control that they did when things are balanced. That kid is your vehicle's front axil when you have a heavy trailer and resultant higher tongue weight on the ball. The WDH works to shift some of the tongue weight back to the front axil so the overall vehicle is back "in balance". (within reasonable variance) It does that by using the tension put on the WDH bars to exert force through the hitch like it's a lever which "effectively" shifts things forward to maintain "normal" balance.
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Old 07-06-2016, 02:53 PM
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Re: WDH vs GAWR

Quote:
Originally Posted by Jim_in_PA View Post
It's not about load...it's about balance. If you put too much weight on the back, it effectively makes the front "lighter" with less contact on the road and that brings a resultant reduction in steering, braking and stability. When your tongue weight gets substantially above 350 lbs (there's a 720 lb max), things start to get "squirrelly" and uncomfortable. This isn't a JGC thing...it applies to any vehicle used for towing and it comes from how levers work from a physics perspective. Think of the teeter-totter in a playground. With the "balance point" in the middle two kids of equal weight/mass can easily lift each other as the ride moves up and down on alternate ends. If you put a kid on one side and an adult on the other, that balance point doesn't work because the "kid side" no longer has the same level of control that they did when things are balanced. That kid is your vehicle's front axil when you have a heavy trailer and resultant higher tongue weight on the ball. The WDH works to shift some of the tongue weight back to the front axil so the overall vehicle is back "in balance". (within reasonable variance) It does that by using the tension put on the WDH bars to exert force through the hitch like it's a lever which "effectively" shifts things forward to maintain "normal" balance.
Thanks Jim. This all makes sense to me and I totally get it, I just don't understand why they wouldn't have more evenly spread out the load rating on the axles then? If the whole idea is to shift weight to the front for stability, why give so much less load capacity on that axle?
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Old 07-06-2016, 03:11 PM
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Re: WDH vs GAWR

It could be because if you think about it, the load on the front is "more fixed" than the load in the back...because of cargo space.
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Old 07-06-2016, 03:34 PM
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Re: WDH vs GAWR

Quote:
Originally Posted by Jim_in_PA View Post
It could be because if you think about it, the load on the front is "more fixed" than the load in the back...because of cargo space.
But not when you add tongue weight and distribute it to the front

I'll try to set everything up with the goal of balancing the Jeep and weigh it on the CAT scale next trip we take. I already know my full fuel but otherwise unloaded curb weight distribution (measured on a CAT scale) gives me only 400lbs to work with on the front and 1100 on the back before reaching the GAWRs. Assuming about 350lbs for passengers in the front (basically middle of the Jeep) and 600lbs of loaded tongue weight distributed evenly across all three axles puts me right near the front GAWR (375ish lbs) so I might have to adjust as necessary since I'll have plenty of margin in the back of the Jeep and can try to put stuff in the rear of the TT as suggested by Phil.

Does that sound about right?
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Old 07-19-2016, 01:25 AM
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Re: WDH vs GAWR

I just got back from a trip to the CAT scale on our way home from using our TT. Currently, my weight distribution hitch was setup up in tire change mode such that the front wheel well measurement was identical loaded vs unloaded, and rear squatted about 1.5''. QL leveled everything out appropriately so I have a good hitch height.

initial Measurements (Jeep unloaded but with gas):

Front Axle Weight: 2840
Rear Axle Weight: 2440

Towing Measurements (Jeep loaded with about 525 lbs of payload including passengers, TT attached and loaded for travel minus water which is right next to the trailer axle):

Front Axle Weight: 2830
Rear Axle Weight: 3580
Trailer Axle: 4360

Based on these measurements I am thinking I should move about 150-200lbs more to the front axle with the hitch, since by the looks of it most of the payload and trailer tongue weight is still being taken on the rear axle which is now close to its limit. That should also lighten the overall vehicle loading by moving more weight to the trailer axle. I am guessing the more even squat guidance for setup should get me close (ignoring the other broader rule of thumb regarding not having the front be lower after setting up the hitch).

Does this course of action jive with all you experts?
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Old 07-19-2016, 04:04 AM
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Re: WDH vs GAWR

hmm.. with the TT and 525lb of payload you added 1100lb on the rear axle and nothing on the front axle.. if you had done the weigh without payload(like the baseline weight) I'd bet you'd be about -300 on the front.. so it looks (to me) like you want to dial in a little more..

What's your tongue weight?
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