[A/S] Re: Overload Devices On Tow Vehicles

["nickcrowhurst" <NickandSandra@xxxxxxxxxxx>]

This is an important and very interesting topic involving some 
complex physics and vital practical consequences. I'd like to add 
some practical measurements to the discussion. I tow a 1988 Excella 
25 with a 2500 Dodge Cummins 4X4. I've used my local weigh station to 
establish the front/rear weights of the solo truck as 4160/2640. When 
the Airstream is attached without load distribution bars, the rear of 
the truck goes down one and a half inches, and the front lifts up by 
one quarter of an inch. When the 1000lb Eaz-lift bars are added, and 
more and more links are dropped, the front returns to the original 
height at 4 links, and the rear moves up half an inch to be one inch 
below its unloaded level. To do this, the Airstream jack has to be 
fully extended on 2 concrete blocks to ease the application of 
tension, and on release, even with the blocks, there are obviosly 
large forces released. I don't think it would be practical to drop 
more links. When taken to the weighbridge with the triler and bars 
fitted,, the front/rear truck weights are 4240/3220, the trailer 
axles (water tank full) support 5680 lbs, with the whole rig 
totalling 13140 with just a driver in the cab in all weighings. The 
bars seem to be distributing 660 lb of tongue weight to the truck, 
but splitting this as 80 to the front and 580 to the rear. This is 
unlike the theoretical ideal in the Airstream manual, where the 66% 
of the load transferred splits equally between front and rear of the 
truck. Could it be that in a truck with stiff front springs, the 
fulcrum of the bars is mainly the front axle, rather than the rear 
axle? (What my physics teacher called a second order lever, rather 
than a first order lever) My interest is on a practical, as well as 
theoretical, level, as I want to be sure that I am making the best 
use of my equipment. Seeing an Argosy trailer rolled on I95 South 
near mile 197 in the Carolinas three weeks ago just heightens my 
interest.