| [GMCnet] Tongue weight [message #123704] |
Thu, 28 April 2011 19:10  |
Kingsley Coach
Messages: 2691
Registered: March 2009
Location: Nova Scotia Canada
Karma: -34
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Netters
Now that I'm home, it's time to begin preps for the next trip.
I have an enclosed trailer and am wondering how much weight I can or should
have on the tongue when connected to the GMC.
What do you need to know to answer this or is there a stock answer?
Thanks guys...
Mike in Antigonish
--
Michael Beaton
1977 Kingsley 26-11
1977 Eleganza II 26-3
Antigonish, NS
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| Re: [GMCnet] Tongue weight [message #123779 is a reply to message #123704] |
Fri, 29 April 2011 08:16  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| Kingsley Coach wrote on Thu, 28 April 2011 20:10 |
Netters
Now that I'm home, it's time to begin preps for the next trip. I have an enclosed trailer and am wondering how much weight I can or should have on the tongue when connected to the GMC.
What do you need to know to answer this or is there a stock answer?
Thanks guys...
Mike in Antigonish
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Mike,
You got the 10% answer, and there are some that say the through the bumper hitch is good for about 500#. (I don't have any actual experience at that hitch load.)
Now, let's get down to the basic facts.
The 500# on the frame hitch is probably reasonable. This is a structural concern and should be tempered so. If you have an old coach that has been in Canadian (or Michigan) salt all its life, you might do well to survey the frame before loading at or above this level. I would not worry about the possible loss of traction. These coaches are so poor in that regard anyway, such a situation should be avoided if at all possible.
The 10% number is a good rule to work with and it has a long history. It is just a coarse rule to keep the hitch load from going negative (big bozo no-no) as no ball hitch is designed to work at negative load. That really comes down to the weight and balance of the loaded trailer. This takes thinking. (A talent rare in the general population, but much less rare on this forum.) If you can load the trailer so its center of gravity (CG) is low enough so acceleration and normal road bounce can't make the hitch load negative (even when leaving that stupid up-hill stop light), then that is all you need. I like to listen/feel for the hitch going slack. The hitch on a GMC is a long way from the driver's seat and if you are not familiar with this issue, there is a simple test. Find a piece of local rough road and have an observer (maybe even you) sit in the back while the rig is accelerated over the rough road. If the hitch goes slack, you will hear and feel it banging. If it does bang, it is time to reload.
By the by...
The sway experienced with a mis-loaded trailer does not come from trailer sway. It is a result of the lateral load that trailer puts on the hitch, but if the tow vehicle rear suspension load is increased it can very effectively mask the poor lateral control.
Just some examples:
There is a picture in the gallery (and I can't find it now) of a rig with 2 each RX7s on a flat trailer and ready to go to the races. If he is running at a 10% tongue load, then that would be way out of band for the rear suspension. I bet he doesn't feel it sway the coach, but he knows it is back there when he tries to make it go.
Under contract from a law firm, I once loaded a covered trailer with furniture and then balanced it to a negative 10% tongue load (a special keeper was added over the hitch/ball to prevent a disaster). It was driven through a number of conditions and neither the dynamic handling or static traction was deemed to be unmanageable. (Caution - professional drivers on a closed course.) We could not create a condition where the rig became unmanageable. The plaintiff had contended that the load in the rented trailer had shifted and caused such adverse handling that it became completely uncontrollable. After reviewing a few thousand feet of chart paper and a lot of hours of film, his counsel told him he was going to loose. Both the vehicle and the trailer manufacture had (unknown to the plaintiff) run almost identical tests long before this. He lost.
Matt (who really likes equalizer hitches)
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Tongue weight [message #123781 is a reply to message #123704] |
Fri, 29 April 2011 08:46 |
PettyVTX
Messages: 363
Registered: April 2011
Location: Winder Ga.
Karma: 1
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Under contract from a law firm, I once loaded a covered trailer with furniture and then balanced it to a negative 10% tongue load (a special keeper was added over the hitch/ball to prevent a disaster). It was driven through a number of conditions and neither the dynamic handling or static traction was deemed to be unmanageable. (Caution - professional drivers on a closed course.) We could not create a condition where the rig became unmanageable. The plaintiff had contended that the load in the rented trailer had shifted and caused such adverse handling that it became completely uncontrollable. After reviewing a few thousand feet of chart paper and a lot of hours of film, his counsel told him he was going to loose. Both the vehicle and the trailer manufacture had (unknown to the plaintiff) run almost identical tests long before this. He lost.
Good.Loaded incorrectly. The way it should be is Looser pays all cost of trial, court costs, and tests. That would stop a lot of frivilous lawsuits wouldnt it.
Ted
Ex Avion now looking for a 23'
Jeep Wrangler Towd
[Updated on: Fri, 29 April 2011 08:48] Report message to a moderator |
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| Re: [GMCnet] Tongue weight [message #123979 is a reply to message #123974] |
Sat, 30 April 2011 18:25 |
tmaki
Messages: 200
Registered: September 2005
Karma: 0
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On 4/30/2011 3:20 PM, Kingsley Coach wrote:
> but what is the procedure for weighing the
> tongue weight?
>
Rather than send you a 26-page owner's manual supplement on
trailer weighing, weight calculations, the effects of
improper trailer loading, etc. that I wrote for a prominent
RV company a few years back (actually an expansion of the
chapter I wrote collaboratively with our engineers at brand
"F" about 25 years ago), just try this:
http://www.rverscorner.com/tongueweight.html
Depending on your trailer, it should get you where you want
to be. Best way is to weigh at a commercial scale [not a
commercial bathroom scale, of course :-) ]. Find your loaded
trailer weight with the tongue jack down and unhooked from
your tow vehicle. Then move the trailer off the scale enough
so that the tongue is off the scale and get a reading.
Subtract the lower number from the higher. The difference is
the tongue weight.
Weighing it this way _does_ require a little more than a few
bathroom items, but gives you a good indication of the total
load WRT correct tire pressures. You could get super tricky
and do a side-to-side weighing if you want to know for sure
if the trailer is loaded evenly. If you always load the same
items the same way, you should only have to do it once or
whenever you change loaded items or loading pattern.
HTH
BTW, the supplement was written partly because a surprising
number of folks actually believe that trailers have infinite
capacity; tires, bearings and axles have infinite capacity;
hitches have infinite capacity; and vehicles towing trailers
(loaded to their infinite capacity, of course) have infinite
power and towing capability. Failures of many or all of
those components seems to indicate that belief to be false.
Toby Maki
'73 Glacier 230
Riverside, CA
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| Re: [GMCnet] Tongue weight [message #124139 is a reply to message #123741] |
Sun, 01 May 2011 20:24 |
jw mills
Messages: 199
Registered: September 2006
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Insufficient tongue weight towing with my 92 Ram Charger put me in a
flat spin. Definitely bad for the seat upholstery in the RC, but the
shinny side stayed up, so all was well. Arch told of a flat spin with
his coach and Sidekick due to road construction. No damage to either
but some time was required to restore normal breathing.
--
Jim Mills
Greeley, CO
1973 CanyonLands 260 TZE-063V100731(under renovation)
1973 Glacier 230 TZE-033V101993
KD0NPU
On Thu, 2011-04-28 at 20:51 -0500, David H.Jarvis wrote:
>
> Yes, total weight.
> There should always be weight on the hitch. Otherwise, the trailer will weave all over the road. Especially on a car.
> The GMC is heavy enough that I don't think it would happen.
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