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04-10-2015, 12:31 PM
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#21
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Moderator Emeritus
Join Date: Sep 2008
Location: Shenandoah Valley of Virginia
Posts: 9,280
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Quote:
Originally Posted by OldCoot
Defies logic!
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Maybe this helps:
Truck without air in rear air bags:
Truck with air in rear air bags:
The front wheel acts as a pivot point, so the area over the front fender (where we take the measurements while setting up a WDH) do not change.
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Chap , DW Joy, and Fur Baby Sango
2017 F350 Lariat CCSB, SRW, 4x4, 6.7 PS
2017 Grand Design Reflection 337RLS
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04-10-2015, 12:42 PM
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#22
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Mod free 5er
Join Date: Mar 2008
Location: Concord, NC
Posts: 24,702
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Quote:
Originally Posted by MtnGuy
Maybe this helps:
The front wheel acts as a pivot point, so the area over the front fender (where we take the measurements while setting up a WDH) do not change.
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Is your toy truck hooked to wdh?
Whatever you want to believe. Good bye!
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04-10-2015, 12:43 PM
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#23
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Senior Member
Join Date: Aug 2014
Location: West Jordan, UT
Posts: 877
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Quote:
Originally Posted by MtnGuy
Maybe this helps:
Truck without air in rear air bags:
Attachment 73797
Truck with air in rear air bags:
Attachment 73798
The front wheel acts as a pivot point, so the area over the front fender (where we take the measurements while setting up a WDH) do not change.
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In my opinion you are not taking into account suspension sag due to the added TW which will affect the area above the wheel. You are correct about the axle being a pivot point (fulcrum)
A statics equation states that weight no matter where it is applied (either forward or behind a fulcrum) acts on the body as a whole. This equation is known as M = F(w) X Distance. Moment equals force (or weight) times the distance. Since the double fulcrum (both axles on a vehicle) is not a solid state fulcrum (the axle due to springs/shocks) the force is transferred across the fulcrum but decreased the further it goes form the place the force is applied. So since the weight is the force and it is applied to the rear of the vehicle that force is transferred across the non-solid state fulcrums and it is absorbed by the suspension resulting in sag.
If your truck in the picture above had suspension and a force applied to the rear of it the picture would not look the same, it would look similar but not the same.
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04-10-2015, 12:55 PM
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#24
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Senior Member
Join Date: Sep 2011
Location: South East
Posts: 996
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Quote:
Originally Posted by MtnGuy
Maybe this helps:
Truck without air in rear air bags:
Attachment 73797
Truck with air in rear air bags:
Attachment 73798
The front wheel acts as a pivot point, so the area over the front fender (where we take the measurements while setting up a WDH) do not change.
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That's one really REALLY big ruler. Nice truck btw.
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2016 Ever-Lite 232RBS
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2018 F250 Lariat (ok but I miss my F150)
Getting old ain't for wimps!!!
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04-10-2015, 01:01 PM
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#25
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Moderator Emeritus
Join Date: Sep 2008
Location: Shenandoah Valley of Virginia
Posts: 9,280
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Quote:
Originally Posted by SuicideSaints
In my opinion you are not taking into account suspension sag due to the added TW which will affect the area above the wheel. You are correct about the axle being a pivot point (fulcrum)
A statics equation states that weight no matter where it is applied (either forward or behind a fulcrum) acts on the body as a whole. This equation is known as M = F(w) X Distance. Moment equals force (or weight) times the distance. Since the double fulcrum (both axles on a vehicle) is not a solid state fulcrum (the axle due to springs/shocks) the force is transferred across the fulcrum but decreased the further it goes form the place the force is applied. So since the weight is the force and it is applied to the rear of the vehicle that force is transferred across the non-solid state fulcrums and it is absorbed by the suspension resulting in sag.
If your truck in the picture above had suspension and a force applied to the rear of it the picture would not look the same, it would look similar but not the same.
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Can you believe I actually understand what you are posting ?? Great explanation.
As you add tongue weight, the back of the truck goes down, and the front goes up. A WDH pulls up on the rear of the truck, putting the lost weight back on the front wheels.
What I have been saying from the start of this discussion, is that rear air bags do little to distribute weight to the front axle.......whether used with or without a WDH. The only weight that it could move forward is the slim "sliver" of truck that is directly over the rear axle before adding air and then after adding air.....because the rear of the truck comes up, there would have to be a tiny center of gravity change over the rear wheels.
In the case of my toy truck: I was trying to make a point as the rear of the truck goes up, the front bumper goes down, but the area directly above the front wheel (front fulcrum) stays the same.
__________________
Chap , DW Joy, and Fur Baby Sango
2017 F350 Lariat CCSB, SRW, 4x4, 6.7 PS
2017 Grand Design Reflection 337RLS
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04-10-2015, 01:15 PM
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#26
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Senior Member
Join Date: Aug 2014
Location: West Jordan, UT
Posts: 877
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Quote:
Originally Posted by MtnGuy
Can you believe I actually understand what you are posting ?? Great explanation.
As you add tongue weight, the back of the truck goes down, and the front goes up. A WDH pulls up on the rear of the truck, putting the lost weight back on the front wheels.
What I have been saying from the start of this discussion, is that rear air bags do little to distribute weight to the front axle.......whether used with or without a WDH. The only weight that it could move forward is the slim "sliver" of truck that is directly over the rear axle before adding air and then after adding air.....because the rear of the truck comes up, there would have to be a tiny center of gravity change over the rear wheels.
In the case of my toy truck: I was trying to make a point as the rear of the truck goes up, the front bumper goes down, but the area directly above the front wheel (front fulcrum) stays the same.
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I agree that air bags alone do little to distribute weight to the front, this action is actually a secondary action or an unitended consequence of leveling a vehicle (front to back-not redistributing weight) and in that we are in agreement. But I will respectfully disagree that the area over the front wheel stays the same, I will say that it does in fact change. It has to change because it can be seen visually in most cases but it may be a small change due to the way suspension systems compensate for weight. This area will also be dependent on what type of suspension and the age of the suspension. I will agree in solid state fulcrums this area remains constant, which can be seen in your picture.
From a theoretical sense with a perfectly working suspension in a controlled environment I would agree mathematically that the area would be the same, but in real world application with suspensions being worn and used over time this area will change, and it will actually change each towing trip unless the exact same conditions and loading are identical each trip as it was to time of initial set up.
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2018 XLR Nitro 36T15
2015 GMC 3500 6.6/Allison
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04-10-2015, 01:27 PM
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#27
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Moderator Emeritus
Join Date: Sep 2008
Location: Shenandoah Valley of Virginia
Posts: 9,280
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Quote:
Originally Posted by SuicideSaints
I agree that air bags alone do little to distribute weight to the front, this action is actually a secondary action or an unitended consequence of leveling a vehicle (front to back-not redistributing weight) and in that we are in agreement. But I will respectfully disagree that the area over the front wheel stays the same, I will say that it does in fact change. It has to change because it can be seen visually in most cases but it may be a small change due to the way suspension systems compensate for weight. This area will also be dependent on what type of suspension and the age of the suspension. I will agree in solid state fulcrums this area remains constant, which can be seen in your picture.
From a theoretical sense with a perfectly working suspension in a controlled environment I would agree mathematically that the area would be the same, but in real world application with suspensions being worn and used over time this area will change, and it will actually change each towing trip unless the exact same conditions and loading are identical each trip as it was to time of initial set up.
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I think we are in agreement !!
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Chap , DW Joy, and Fur Baby Sango
2017 F350 Lariat CCSB, SRW, 4x4, 6.7 PS
2017 Grand Design Reflection 337RLS
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04-10-2015, 01:29 PM
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#28
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Phat Phrog Stunt Team
Join Date: Aug 2011
Location: Iowa
Posts: 34,507
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I need a drink
TURBS
08 duramax tuned n modded, 32bhok Sabre
2015 camping "2 nights"
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04-10-2015, 01:35 PM
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#29
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Senior Member
Join Date: Aug 2014
Location: West Jordan, UT
Posts: 877
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Quote:
Originally Posted by MtnGuy
I think we are in agreement !!
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When I first read the thread I thought you were saying that a WDH and then adding bags does nothing to transfer weight to the front, but yes we are in agreement that you should use a WDH to transfer weight to the front then you should use bags to level (front to back, this is not for true weight distribution purposes) the entire rig out. Correct?
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2018 XLR Nitro 36T15
2015 GMC 3500 6.6/Allison
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04-10-2015, 01:37 PM
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#30
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Senior Member
Join Date: Feb 2015
Posts: 304
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I simply suggested the air bags to stiffen the rear end. These half ton trucks mine very much included, are soft in the rear end. After I get my wdh set I add air to stiffen the rear springs a bit to make the ride better and less porposing as you hit dips, bridges, etc... After all in a perfect world, don't we want the TV and TT to ride as close to level as we can, and so they travel more as one unit going down the highway.. If I'm wrong here I'm sorry and won't add any more of my 2 cents... 😝
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04-10-2015, 01:46 PM
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#31
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Moderator Emeritus
Join Date: Sep 2008
Location: Shenandoah Valley of Virginia
Posts: 9,280
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Quote:
Originally Posted by SuicideSaints
When I first read the thread I thought you were saying that a WDH and then adding bags does nothing to transfer weight to the front, but yes we are in agreement that you should use a WDH to transfer weight to the front then you should use bags to level (front to back, this is not for true weight distribution purposes) the entire rig out. Correct?
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Correct. Sometimes I have trouble putting my thoughts down into words.
I more question: When using a properly setup WDH, distributing weight back to the front axle of the truck, would a fraction of that weight be taken back off of the front axle if you inflate the rear air bags after installing spring bars ?? My thoughts with that is that once you lift the back end of the tow vehicle some, that relieves some of the pressure from the spring bars, thus taking some weight off of the front axle....however minimal that would be.
__________________
Chap , DW Joy, and Fur Baby Sango
2017 F350 Lariat CCSB, SRW, 4x4, 6.7 PS
2017 Grand Design Reflection 337RLS
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04-10-2015, 01:47 PM
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#32
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Senior Member
Join Date: Aug 2014
Location: West Jordan, UT
Posts: 877
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Quote:
Originally Posted by dsjohns71
I simply suggested the air bags to stiffen the rear end. These half ton trucks mine very much included, are soft in the rear end. After I get my wdh set I add air to stiffen the rear springs a bit to make the ride better and less porposing as you hit dips, bridges, etc... After all in a perfect world, don't we want the TV and TT to ride as close to level as we can, and so they travel more as one unit going down the highway.. If I'm wrong here I'm sorry and won't add any more of my 2 cents... 😝
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No you are correct, the title of the thread kinda threw me at first, you do not use bags for weight distribution in a traditional sense, the weight distribution is a secondary consequence (and small consequence) to lifting the rear rather than the primary and intended consequence of a WDH. That is what a WDH is for, bags are to aid the WDH in getting the entire rig level.
TURBS- I will take that drink with you.
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2018 XLR Nitro 36T15
2015 GMC 3500 6.6/Allison
Nights Camped (2018-16) (2017-16) (2016-13) (2015-13)
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04-10-2015, 01:55 PM
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#33
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Member
Join Date: Feb 2015
Posts: 247
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This is a particularly interesting thread. I'm not taking sides although like everybody else, I'm certain that I have the correct answer. Here's what I've learned: as in all things internet, one has to be very cautious about who/what to believe.
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04-10-2015, 02:01 PM
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#34
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Senior Member
Join Date: Aug 2014
Location: West Jordan, UT
Posts: 877
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Quote:
Originally Posted by MtnGuy
Correct. Sometimes I have trouble putting my thoughts down into words.
I more question: When using a properly setup WDH, distributing weight back to the front axle of the truck, would a fraction of that weight be taken back off of the front axle if you inflate the rear air bags after installing spring bars ?? My thoughts with that is that once you lift the back end of the tow vehicle some, that relieves some of the pressure from the spring bars, thus taking some weight off of the front axle....however minimal that would be.
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Theoretically yes because you are know changing the angle of the moment and therefore changing the transfer of force across the fulcrums plus the suspension now changes in order to cope with this, you are only changing the angle a few degrees (if that) but it would change the value.
But the bags kinda compensate for this by adding that sliver of weight back to the front since the back was raised. To calculate this a vector analysis would have to be conducted in order to find the transfer lost from the WDH and how much the bags added when inflated. My theory would these numbers would be pretty close or it would be negligible considering you had the correct torsion bar values to begin with.
I was kind of a nerd in my past life......
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2018 XLR Nitro 36T15
2015 GMC 3500 6.6/Allison
Nights Camped (2018-16) (2017-16) (2016-13) (2015-13)
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04-10-2015, 02:03 PM
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#35
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Always Learning
Join Date: Nov 2011
Location: Four Corners, FL
Posts: 21,890
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Quote:
Originally Posted by Filthy Beast
Easy to prove or disprove. If someone that contends it does distribute weight forward. Take the rig to a scale. Take a picture or get the weight ticket to show weights, then add air to the bags and get another ticket with the new numbers. I would be interested in the results just for curiosity as I do not have a tt.
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Heck, I'm curious enough- I'd be willing to pay for the scale costs if someone wants to go do this.
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04-10-2015, 02:45 PM
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#36
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Senior Member
Join Date: Sep 2014
Location: Wisconsin
Posts: 691
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WOW!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!
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04-10-2015, 02:53 PM
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#37
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Senior Member
Join Date: Oct 2012
Location: Oregon
Posts: 1,002
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If you have air bags and a friction base WD then adding air after hitching up will reduce the friction on the bars. If using those friction plate devices then no sway control will be lost.
If adding air after hitching up you also lose any weight transferred to the TT and front because you are removing tension from the spring bars.
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04-10-2015, 03:01 PM
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#38
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Senior Member
Join Date: Aug 2014
Location: West Jordan, UT
Posts: 877
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Quote:
Originally Posted by goduc
If you have air bags and a friction base WD then adding air after hitching up will reduce the friction on the bars. If using those friction plate devices then no sway control will be lost.
If adding air after hitching up you also lose any weight transferred to the TT and front because you are removing tension from the spring bars.
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I thought we had exhausted this but, yes you are correct you will reduce the friction in effect losing some sway control, you are not entirely correct on losing "any weight transferred", the only way you lose all of the distributed weight is if you inflate to the point where there is no tension on the bars. As long as there is tension on the bars some weight is being distributed. Not trying to be nit-picky but "loose verbiage and descriptions" is how i think we got into this mess.......
I will leave it at that and I have no more to add unless someone wants to post measurements and weight tickets then I will gladly run the vector analysis/matrix in MATLAB then we can compare the tickets to the theoretical/mathematical part for correlation of the two.
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2018 XLR Nitro 36T15
2015 GMC 3500 6.6/Allison
Nights Camped (2018-16) (2017-16) (2016-13) (2015-13)
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04-10-2015, 04:31 PM
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#39
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Senior Member
Join Date: Feb 2015
Posts: 847
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I think of the rear end as the pivot point of a teeter totter. raising the fulcrum does nothing to change the load dynamics other than caster and headlights.
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04-12-2015, 01:40 PM
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#40
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Senior Member
Join Date: Mar 2015
Location: North Plains, OR
Posts: 253
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Quote:
Originally Posted by MtnGuy
Correct. Sometimes I have trouble putting my thoughts down into words.
I more question: When using a properly setup WDH, distributing weight back to the front axle of the truck, would a fraction of that weight be taken back off of the front axle if you inflate the rear air bags after installing spring bars ?? My thoughts with that is that once you lift the back end of the tow vehicle some, that relieves some of the pressure from the spring bars, thus taking some weight off of the front axle....however minimal that would be.
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Your thoughts are correct. After I set up my WDH, I add air to my bags. When I do my measuring, I measure my tire to fender clearance. If I add enough air to the bags to make my rear tire/fender clearance stock, my front tire/fender clearance goes up about 1/4". This tells me that the WDH is not putting as much weight to front axle.
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