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09-03-2007, 01:19 PM
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#1
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Montana Master
Join Date: Jan 2005
Location: Ephrata
Posts: 757
M.O.C. #2801
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Need engineer calculations.
The pin weight on our Big Sky is 3380 pounds and it is all centered on the rear axle of our truck and with the weight of the truck at the rear axle I am over 400# the gross axle weight. I have lots of room to spare on the front axle.
How far would I have to move the hitch in the back of the truck forward to shift 400 pounds onto the front axle? Not sure if I want to do it but it's worth thinking about.
Thanks for any help.
Dick
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09-03-2007, 01:57 PM
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#2
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Montana Master
Join Date: Jul 2003
Location: Clearwater
Posts: 10,917
M.O.C. #420
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If I recall your hitch should be placed in such a position that the center of the pin would be 1/2" to 1" in front of the rear axle. Not sure if this would be enough to shift the 400# of weight or not.
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09-03-2007, 02:04 PM
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#3
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Montana Master
Join Date: Jan 2005
Location: Ephrata
Posts: 757
M.O.C. #2801
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Glenn, It's interesting to learn that my hitch is just a hair behind the rear axle as the front axle is 100 pounds heavier after I take the Monty off. very interesting.
Dick
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09-03-2007, 02:12 PM
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#4
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Montana Master
Join Date: Feb 2007
Location: Winfield
Posts: 7,327
M.O.C. #6846
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Simple math would tell you that to take 10% off of the pin weight, you would have to move 10% of the distance between the tires (wheelbase) forward. I am sure this is not exactly correct (calculation-wise), but it does provide the basic geometry. I don't believe that route is the proper solution to your problem. A better approach would be redistributing the weight within the 5er. Counterbalancing can also be obtained by hauling fresh water if the fresh water tank is on the rear of the unit. Hopefully, some more experienced members who have had similar trials will chip in, (I will say that personally -OPINION-OPINION- 10% over the rated weight would not concern me, because (even though I have been shot down on this statement before) there is no way that these specifications are put out with zero tolerance. Any engineering calculation contains a safety factor (everything I do and design always has a minimum safety factor of 30% built in). I am not an automotive engineer however, so here are the bullets and here is the gun, Shoot away!! As always this is my personal (not professional) opinion and should be treated as such. No guarantees or warrantees are implied or implicit.
Bingo
On edit:
I saw the post about being behind the axle, and that possibly could be very relevant. Obviously, from your statement, if you move the hitch slightly forward of the axle, you WILL gain the 100 pounds, and slightly in front of the axle will gain a little more. This may make the weight redistribution a little more attainable. I would be interested in your new numbers if you do move the hitch slightly forward of the axle (as Glenn said - the proper installation)
__________________
Bingo and Cathy - Our adventures begin in the hills of WV. We are blessed by our 2014 3850FL Big Sky (previous 2011 3750FL and 2007 3400RL) that we pull with a 2007 Chevy Silverado Classic DRW CC dually.
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09-03-2007, 03:39 PM
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#5
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Montana Fan
Join Date: Sep 2006
Location: Olympic Mountains
Posts: 130
M.O.C. #6254
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If you have a 156" wheelbase length, then you would have to move your hitch about 18.5" forward to place 400 lbs. on the front axle and 2980 lbs. on the rear axle. This is figured by using "weights & moments" I learned in engineering school many years ago. Of course, I could have forgotten what I learned so I need to add a disclaimer.
Ken
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09-04-2007, 08:21 AM
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#6
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Montana Fan
Join Date: Jul 2007
Location: No Telling
Posts: 207
M.O.C. #7430
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Regarding the 30% safety factor mentioned earlier. I'm not an engineer, but do have some experience with GWs as they pertain to the aircraft industry. Airplanes, like cars/trucks, have a GWR, and should that rating be exceeded the airplane is not going to break. Same for cars/trucks. Agree there is a fudge factor built in. However, that factor is designed to protect the vehicle should it be subjected to unplanned stress. If an airplane runs into turbulence or a car/truck drops into a huge hole, and they are at GW, the components would be subjected to stresses that would exceed the GWR. Therefore, the fudge factor is there, but it is not there so we can exceed the rating, it's there to protect us and our vehicles when they are subjected to conditions which make them go over their ratings.
That sure is a lot of PW. Even with my dually, that PW plus what I usually carry, would put me just about at GVWR.
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09-04-2007, 02:47 PM
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#7
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Montana Master
Join Date: Oct 2004
Location: Sulphur Springs
Posts: 748
M.O.C. #2220
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I make my living around big trucks and it is part of the safety factor to shift the fifth wheel forward to distribute weight to front axle for better braking control. Key is to not OVERLOAD font axle. In my TV I had the hitch professionally installed and it is 4" forward of center rear axle.
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