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Old 05-09-2014, 09:12 AM   #1
Mez
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What exactly do Weight Distibution Bars do?

OK besides the name making it obvious lol!

I am curious. If my payload is about 680 after the full tank of gas, 4 people and two small dogs. If I get a WDB what does that add to my payload?

The camper I am looking at right now has a HW of 680, and I actually have 700 PL but once propane is filled I figure it will be less.
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Old 05-09-2014, 09:21 AM   #2
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OK besides the name making it obvious lol!
I am curious. If my payload is about 680 after the full tank of gas, 4 people and two small dogs. If I get a WDB what does that add to my payload?
The camper I am looking at right now has a HW of 680, and I actually have 700 PL but once propane is filled I figure it will be less.
Mez
See: HowStuffWorks "How Towing Weight Distribution Systems Work"
Mel
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Old 05-09-2014, 09:25 AM   #3
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No it does not. It transfers some of the added weight to the front axle but total payload stays the same.
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Old 05-09-2014, 10:30 AM   #4
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Payload is always the weight of the vehicle less the curb weight as equipped, and is established by the manufacturer. Can't change it. Because the tongue weight of some travel trailers can cause the rear of the tow vehicle to sag too much, a WD hitch, as mentioned above, is used to more evenly distribute the weight between the tow vehicle axles, or stated differently, move some of the tongue weight off the rear axle and onto the front axle.
With a hitch weight of 680 and PL of 700, you don't have any wiggle room to do it right.
Joe
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Old 05-09-2014, 11:04 AM   #5
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Payload is always the weight of the vehicle less the curb weight as equipped, and is established by the manufacturer. Can't change it. Because the tongue weight of some travel trailers can cause the rear of the tow vehicle to sag too much, a WD hitch, as mentioned above, is used to more evenly distribute the weight between the tow vehicle axles, or stated differently, move some of the tongue weight off the rear axle and onto the front axle.
With a hitch weight of 680 and PL of 700, you don't have any wiggle room to do it right.
Joe
Thanks, so it just relieves all pressure on the back axle and maybe helps prolong the wear and tear on the vehicle?
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Old 05-09-2014, 11:29 AM   #6
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If you have too much weight on the rear axle (besides possibly overloading it) you won't have enough on the front axle to steer correctly, and the front tires will break traction when braking hard. Also, this tail-heavy situation almost always results in excessive sway and potential loss of control.
Check your owners manual--it should state the max tongue weight for bumper pulls with and without WD hitch.
If you have never towed with a light front axle/overloaded rear axle, once you do you will probably never forget it.
Wear and tear will happen no matter what the setup, you just need correct weight distribution (balance) to be safe. I guess the first item to go if tail-heavy would be tires/tire wear...
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Old 05-09-2014, 04:50 PM   #7
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My 35 years teaching automotive taught me to always try to make things as simple as possible to understand. You reach more kids that way and from there they can elaborate on the principles learned.

Think of it like a wheel barrel. Most of us can relate to a wheel barrel. When you grab the handles and lift you are transferring the weight that was on those legs to the front wheel. You still have the same amount of weight but you've shifted it forward. A WDH is the same concept only it allow you to adjust how much weight you shift and in which direction you shift it.



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Old 05-09-2014, 09:07 PM   #8
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If my payload is about 680 after the full tank of gas, 4 people and two small dogs. If I get a WDB what does that add to my payload?
I assume by "payload" you mean the unused GVWR available for tongue weight. Thus "payload" would be the GVWR of the truck minus the weight of the wet and loaded truck without the trailer tied on.

Ideal weight distribution is about 20% to 25% of tongue weight distributed to the front axle, 20% to 25% distributed to the trailer axles, leaving 50% to 60% on the rear axle of the tow vehicle.

Compared to the same exact truck with the same exact load without a WD hitch, the WD hitch will slightly increase your gross vehicle weight (GVW) on the 2 truck axles, because of the extra weight of the heavier hitch head and the weight of the spring bars of a weight-distributing system. But it will also slightly decrease your GVW because the WD hitch distributes some of the weight back to the trailer axles. The net effect should be about a hundred pounds or so more wiggle room before you exceed the GVWR of your tow vehicle.

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The camper I am looking at right now has a HW of 680, and I actually have 700 PL but once propane is filled I figure it will be less.
How did you determine the hitch weight of the trailer? If that is the published hitch weight in the trailer's brochure, then that is the "dry" weight of that trailer with no options and empty water and propane tanks. Your actual wet and loaded hitch weight will be about 12% to 15% of the weight of the wet and loaded trailer.

Example: new Keystone Hideout 25RKS has a dry hitch weight of 700 pounds, which is 11.6% of the dry (shipping) weight of the trailer. Shipping weight is 6,053 pounds plus cargo capacity 1,647 pounds for a GVWR of 7,700. When loaded to the GVWR, your hitch weight is going to be about 11.6% of 7,700, or 893 pounds. So if you have only 700 pounds of weight capacity available for hitch weight, then you're going to be overloaded.

What will a WD hitch do for you? If you are darned good at fine tuning your WD hitch, then you should have about 20% to 25% of the tongue weight distributed off the truck axles and onto the trailer axles. With tongue weight of 893 pounds, that's at least 178 pounds distributed off the truck axles and back to the trailer axles. Reduce that by about 50 pounds for the extra weight of the WD hitch, and you have reduced your overloaded condition by about 128 pounds.

Restated another way, if you have 800 pounds tongue weight (as reported by a tongue weight scale), and your WD hitch is adjusted to distribute that tongue weight 20/60/20 percent, then with the spring bars tightened your front axle weight should increase by 160 pounds, the trailer axles weight should increase by 160 pounds, and the rear axle weight should decrease by 320 pounds compared to the axle weights without the spring bars tightened.
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Old 05-10-2014, 11:08 AM   #9
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Another example: The RV trailer with 680 pounds dry hitch weight, which is 12% of the 5,667 pounds dry weight of the trailer that has GVWR of 6500 pounds. Wet and loaded trailer will weigh 6,500 pounds with 780 pounds hitch weight.

With the WD hitch installed, but without the spring bars tightened, the weight on the rear axle will be more than 780 pounds because the see-saw effect comes into play. Some of the weight that was on the front axle gets shifted to the rear axle when you drop the hitch onto the ball that is 4' behind the rear axle.

Weigh the truck on a CAT scale with the spring bars not installed to get the "before" weights. Then install and tighten the spring bars and weigh the rig again to get the "after" weights. If your WD hitch is adjusted to result in 20/60/20 distribution, then with the spring bars tightened the front axle should have about 136 pounds more weight on it, the trailer axles should have about 136 pounds more weight on them, and the rear axle should have about 272 pounds less weight on it. So the net reduction of weight on the truck axles is the 132 pounds that was distributed to the trailer axles. So you could say that your payload increased 132 pounds, but that would be a misnomer.

I suspect the answer to your question of "If I get a WDB what does that add to my payload?" when towing the example trailer, it increases the hitch weight you can haul without being overloaded by about 132 pounds. Granted, the actual payload of your pick didn't change, but 132 pounds of the hitch weight of that trailer was distributed back to the trailer axles and off the truck's axles.

But that 132 pounds number is comparing the trucks with the same hitch head installed. Most WD hitch heads weigh about 50 pounds more than a simple weight-carrying drawbar and ball, so instead of 132 pounds difference, the actual difference is less than 100 pounds. With my ProPride hitch that weighs over 100 pounds more than a drawbar+ball, the difference in tongue weight I can have with my ProPride hitch compared to a drawbar+ball is not worth computing.

But as the gun nuts say, you'll take my ProPride hitch from me over my cold, dead body. Yeah, it's expensive. Yeah, it's heavy. But when properly adjusted, it results in a wonderful towing experience when dragging a travel trailer.
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Old 05-18-2014, 06:13 PM   #10
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All GM heavy duty trucks do not require a WD hitch as their frames are strong enough to take the stress. Many tow vehicles do not have a strong enough frame or may have a unibody construction without a frame and they need assistance of special WD hitches. Weigh your truck without the trailer at a CAT scale and then weigh it with the trailer in tow and compare the weight on the front wheels. I doubt if even 100 lbs. of the trailer tongue weight is transferred to the front wheels. On my truck with 3200 lbs. added to the rear wheels the increase in the front wheels was less than 100 lbs.
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