Twin beam Design Considerations

Some folks believe very strongly in over kill. I am one of them. Paranoia, is most easily destroyed through such practices, and over kill has the ability to bring peace of mind to the builder. Whether over kill is actually beneficial or not, it most certainly is to the one concerned, so I shall attempt to bring peace of mind to even the most cautious of you.

In the design of HellTrike, I began with two 3” X 2” X 11 gauge beams. Now THAT was over kill. If you note, the SAME amount of area is welded to the torsion bar as is with the 2” X 2” beam! Most trikes only have one 2” X 2” tube that constitutes the front end frame work. This equates to only 4”of weld at the torsion bar to beam, at the weakest point. When I designed HellTrike2, the basis for this website, I cut and welded 5” X 3” X 1/4” steel butt plates to the sides of the twin Beams and the torsion bar. I wonder how high you would have to drop that from a building before it broke?

Needless to say, it WAS OVER KILL. In the newer versions of Helltrike the bottom bracing and the standoffs to the torsion bar add not only leverage to the beam to torsion bar strength, but it also ties the front of the twin beam to the torsion bar by means of the pan side rails. In this manner, vertical, as well as horizontal stress are shared by both the twin beam, and the floor pan frame. The surface area, although appearing small because of the spread, is roughly 10” of weld, beam to torsion bar.

Stress on the torsion bar to frame is NOT, in my opinion, as severe as one would think in a design like HellTrike. The vertical motion not absorbed through the front or rear shocks, is mostly dissipated in the axles. Think of this as a teeter totter, with the weight being distributed slightly forward, because of the fulcrum point, which is basically the rear wheels. In this, the most stress from bouncing off road will appear at the load point. For lack of terminology, we shall call it that. This would be the central point on a straight beam where the load is supported. If you imagine a man on a tight rope, you will get the picture.

Now if the tight rope were in fact a steel beam, and if the extreme ends of that beam were to suffer vertical shock, it would be the section that does not respond as rapidly due to the weight on it where the stress would be exhibited. On HellTrike that would be the drivers seat. However, since THAT POSITION is so close to the torsion bar, in fact, nearly directly over it, that stress is shared , with most of it going directly to the torsion bar. The passenger however, is totally out of the picture, as this riding position is almost directly over the wheels, or the fulcrum point.

The lateral stress, which is probably as great or greater than vertical stress on a trike, is exhibited while turning. As you turn left to right, the front end pulls the beam side to side, with the greatest stress being directly on the beam to torsion bar joint, because it is at the very end of the lever. Rather than that stress being at the end of a lever, such as on a single beam trike without any floor side supports, on HellTrike it is locked out through the floor pan framework. Therefore lateral stress on HellTrike is sent from the front of the lower twin beam, through the side rails to the torsion bar, to the outer edges of the trike, relieving any stress from the beam to torsion bar joint.

So, all in all, for those who still need more, make and use the side butt plates. They look good, they make you feel good, And if your welding isn’t that good, they give you a certain amount of insurance while tearing around the couch or riding up and down the stairs. It doesn’t hurt a thing, and if I had someone to fabricate them for me, I might even put them on. I just find them difficult to fabricate, and I don’t need them.

It has been foremost in mind, that if I were to hit something that would break that beam loose, I wouldn’t be around to see it anyway. I often let others take it on trips. HellTrike is used off road. I jump curbs with it, it has hit a tree, it has hit a brick building, and it even ate a van. Nothing twisted or fractured, with the exception of one joint that I had only tack welded, and had forgotten to complete, and that was the lateral brace from the pan to the shock tower on the left side. The van was totaled by the insurance company. HellTrike lost a little paint.

Slacker G