What's the advantage of the frame design on our new TT?

They are both strong, but only as strong as the material used! the differences come from the design of the trailer.

As 69Avon points out. The manufacturer choose that frame design because it met their design goals.

I bought my TT to enjoy travel and camping. Life is too short to second guess alternate TT construction methods.

Being a Civil Engineer and not a Mechanical Engineer, I can only comment on what I see. I assume others have the credentials to confirm or deny the stresses and strains involved. I repeat, the less welding on a frame, whether it is on a dump truck, backhoe, or trailer, the better it looks to me. The OP asked what advantage the stepped frame coupling has. I have not heard a definitive answer yet. If it is that the straight frame is deficient, then it would be an easy cure to upgrade the section modulus of the framing material.

TomG2 wrote:
I see a frame that has a underslung connector as something that a freshman welding class might come up with when they realize the trailer needs some connection to the tow vehicle. Yes, it can be strong, that is not my point. When I look at the workmanship in the typical trailer, I buy what has the fewest welded on pieces.

While I understand your thinking what you may be inadvertently doing is getting the Less strong structure. Of course it depends on the design and the materials. They have to be consistent with the expected loads and the safety factor.

Properly welded joints are often stronger than the surrounding material. As was evident by the pics of the failure posted here.

Sometimes the actual best condition for loading a beam is not the intuitive one. As in the case of the A-frames on trailers.

I see a frame that has a underslung connector as something that a freshman welding class might come up with when they realize the trailer needs some connection to the tow vehicle. Yes, it can be strong, that is not my point. When I look at the workmanship in the typical trailer, I buy what has the fewest welded on pieces.

jmtandem wrote:

There is a fundamental misundrstanding about the dropped or "stepped frame as you call it.

You might benefit from knowing who you are referring to in your comments. I never refered to any frame as a 'stepped' frame. That was TomG2, not me.

Yes I understand that. Thank You. I was addressing myself this way to both of you that had essentially the same argument about the frames. I used both references just to be clear.

I would think the thickness of the metal of the frame would be a bigger influence to failure then method of construction. I know a lot of lite TT use a very lite frame.

The discussions that ensued a few years ago regarding frame failures had finger pointing on both sides of the issue. It was argued that the frame manufacturer(s) built frames to the specifications of the trailer manufacturer. The specs were too weak. Others felt that poor welds, poor construction, etc. at the frame builder caused the failures. Still others including Weekend Warrior indicated that the overloading by owners of more weight than was designed for caused some of the triple axle frame issues at the axle area. Weekend Warrior also incoporated the side walls into the calculations for overall strength and the triple axle length created structural frame issues if the rear toy area was overloaded. At the end of the day those that had frame issues were offered a fix by Weekend Warrior to strengthen the A frames. There were enough to warrant a frame fix kit. It is important to recall that Weekend Warrior was not just the inception for toy haulers but also the dominate force in that RV type for many years. Many many WW toy haulers were made. Even a small percentage of failures were a lot of trailers. Airstream and Keystone also had frame failures. Airstream 'A' frame issues are often cited as being due to excessive aggressive weight distribution hitches. Airforums discusses this. It was not just WW. I have no dog in the stacked frame issue, my comments were directed to past frame failures not being all that rare. Mine has a straight thru frame since you asked and so far no issues.

There is a fundamental misundrstanding about the dropped or "stepped frame as you call it.

You might benefit from knowing who you are referring to in your comments. I never refered to any frame as a 'stepped' frame. That was TomG2, not me.

For those that have pulled TT's with the lower profile as well as the taller profile as described, did you notice any difference with crosswinds while having more 'sail' area ?
I would imagine the TV used would come into play.
It might not be as much a difference towing with a 350 dually opposed to a large suv or 150.

jmtandem wrote:

Which one's of us would purchase a truck with a frame that was overlapped and welded together in a typical RV factory?

Excellent point. And a point that seems to be lost on overly optimistic reliability assertions. Anybody that has interest in frame failures can research Lippert (and perhaps others) frame failures. Lippert builds about eighty percent of all travel trailer RV frames. There were documentable Lippert frame failures in both fifth wheels and travel trailers. The Weekend Warrior forums well chronicle frame issues by owners for travel trailer toy haulers 'A' frames and the frames near the triple axle on those units. Keystone has had to fix a number of fifth wheel frames built by Lippert. Many that have been on these and other RV forums remember the many frame failure threads. In the past five or so years frame failures seem to be less or folks are not posting about them.

One exception is Northwood Mfg that makes their own frames and they are overly built and not prone to failure.

There is a fundamental misundrstanding about the dropped or "stepped frame as you call it.

First of all. The main reason for the failure in the pics above is POOR DESIGN.

Tubular rectangular steel box sections are INTENDED to be loaded from the TOP or the narrow section. They are not meant to carry anywhere near their capacity in a butt joint as shown in the pictures. This was simply THE WRONG way to load that steel member.

The dropped frame IS THE CORRECT way to load that steel member, with the load on top of the narrow section and wedled there.

It is not a financial choice it is proper design.

Now that is not to say that you cannot use the box sections in other ways, you can. But you cannot load them to the same limits.

This is why I have said that the dropped frame will be stronger and ultimately more reliable. (All design elements being equal)