DmaxEter

WOW
Just for scientific experimetation tonight at work I set a piece of this 1" plate up with a oak block under each end and lowered a front load garbage truck onto it. I deflected maybe 1/2" but didnt think of holding that deflection once the load was lifted off. This truck on the steer axle is upwards of 18,000lbs and I know i will never have that much on it. I figure worse case it will act like a sho-nuff heavy duty leaf spring going down the road and absorb some of the road shock.

I will weld a C channel across the bottom to help out a little.

P Kennedy

No need to weld another C channel to the bottom just weld 2 bevelled stress plates across the bottom of the existing C channnel to form a vertical truss and it will not bend. The weak spot in your hitch is where the ball passes through the C channel because at this point only the web thickness of the C channel is supporting it. 2 pieces of 3/8" plate 18" long 2" wide tapering to a point or more with the full width 6" long will stop this deflection with the way it is built from the pictures. The side brackets are strong enough but when possible the mount point should be spread along the frame 12-18" on the tube style frame due to the wall thickness. Inserts through the frame with bolts all the way through double the holding capacity of the hitch in these light wall frames. The inserts can be MIG or stick weld "tacked" on top edge to hold them in place without heating the frame causing stress cracks. The inserts should be the exact length of the frame width so as to sandwich them when the bolts are tightened. This also gives the bolts extra strength producing 2 shear ponts instead of 1 like on a standard C frame. PK

DmaxEter

Good info there!
What about my setup with a 1" thick x6" wide 52" long solid piece spanning across the frame? Is there any need to worry about it bending with the road shock there?

On these tube frames that we are dealing with here, where the hitch mount the frame is doubled up because the rear section slides into it. Right where they slide together is the hitch muonting point so I figure without going out and measuring, the frame is about 3/8" thick at this point.

P Kennedy

It should be just fine as long as you do not make the rear springs too stiff down the road and transmit the pressure into the frame section between the spring hanger mounts. The shorter the mount on the frame longetudely the more concetrated the weight in 1 specific section of the frame between the spring hangers. This also depends on the lenght of the overlap where the frame section is joined, the longer the lap the more stregth it has. One of the interesting things happening out there is the "Cab and Chassis" truck configurations are all coming back out on the market with "ladder type" C channel frames. Both GM and Dodge-07 C&C trucks have C channel sections behind the cab for mounting purposes. GM discovered this a couple of years ago and rectified the problem, Ford has maintained the C channel all along-YYYYYY? 6-8" X 1/2" web C channel has as much strength or more in this application for rigidity as 1" X6" flat bar and is 1/2" the weight! Depends on what material is easiest to get your hands on both are overkill but secure. PK

Alec

To reiterate what P Kennedy said a little bit:

Overkill means that you are carrying around unnecessary weight -- which means less load capacity and or less fuel milage. You may or may not care.

Most of the strain in a structural part is taken by the surface of the part: So, for the beam you are making to go between the fram rails, and carry your hitch, the top 1/8th and bottom 1/8th of that 1" plate are doing most of the work in the up and down, and the front and rear 1/4" or so are doing most of the fore & aft work. The further apart those surface are, the more strain they can withstand. This is why the wide-flange, or "H-beam", is used so often -- most of the material is at the surface, where the strain is, and those surfaces are separated as much as is practical.

Additionally, the greatest stress is in the middle of that beam, which also is where the hitch must attach, and many of these designs actually have less material there, because they are cut out, or drilled out, for the hitch mounting.

For this application, a four inch square tube with 1/4" walls will give you a stronger hitch for about 2/3 the weight of that flat plate . . . It will also be much less springy torsionally (when you pull your trailer, the flat plate will want to twist, because the hitch is actually up off of it).

The tube can be notched on the ends to hang down inside the frame.

The other very good point that was made is with these thin walled high tensile box frames, you need a large attachment area to distribute the load from the hitch to the frame.

I hope that made sense and was a little helpful.

csramsey640

I agree and disagree. I too went heavier than needed, BUT in the days with so many lawsuits, I believe the ones that "look cheap" are still very functional, reason being because they pay enough $$ for liability insurance shall something come back, and if for some bad reason it did, Im sure they want covered incase John Public files a lawsuit.

If the old girl says 25k, chances are, youll be fine to 25k.

Now, for flat out commercial use, I would want a hitch that is designed to handle...commercial service.