Originally Posted by Cliffy
The concrete is poured in given length blocks on the road and at hiway speed it reacted with the axle spacing in a synchronous manner to amplify the bounce at speed and cause the wheels to lift off the road.
I have not seen this mentioned anywhere in a long time. I have encountered this exact phenomenon on the interstate in northern California. Just as you say, the concrete sections are all poured in the same fixed lengths. The slabs have tilted down (or up?) on one end and as you drive over each joint, there is quite a thump. I've broken the cords in several tires before an had to replace them. Apparently the spacing of the semi truck axles and natural spring rate of the truck suspensions coincides with the joint spacing and pounds them into the ground. It's like driving on a washboard. Must be bad for ST tires.
When you sight down the underside of our frame, you can see quite a bit of sag on the underside of the I-beam. That tells me that the frame is not capable of carrying the static load of the trailer structure and components above the frame. When driving and bumps are hit, the trailer's frame gets thrown up and it will suffer excessive vertical movement. And that movement will be concentrated around the axles which are a pivot point.
The frame is made from 3 pieces of 1/8" sheet steel welded together to *look* like an I-beam. It has inadequate cross-bracing and it is not reinforced whatsoever in the area around the spring hangers. The spring hangers are bent to one side and up to 5/8" out from top to bottom of the hanger. When the trailer is up on a hoist, the hangers all bend to the opposite direction. The frame is so flimsy the spring hangers flop from side to side. One photo below is at a cg on the way out and when did a sharp turn to leave. You can see how the tires go wonky and way out of camber because the frame and axles are flexing so much. The frame shop found the same thing by just pushing on one side of the trailer. Bad, bad, bad...
You can imagine how much the wheels/tires must flop around when towing this trailer.
The I-beam flanges are distorted in each location the hangers are attached due to the constant side to side movement while towing this trailer. This distortion in the flanges will cause stress/fatigue cracks in the frame. Again, bad, bad, bad... Some TTs have a length of 2x2 square tubing welded to the underside of the flange to distribute the load along the beam. Some trailers also have what are called gussets welded from the outside lower part of the beams to part way up the side of the vertical part of the beam. These are usually at a 45 degree angle and stiffen things up a lot.
So with a frame that is weak in a vertical direction and also a frame that flexes from side to side, this will lead to frame cracks and failed welds in short order. We've got under 500 miles on this thing and already have signs of failure. We discovered bent spring hangers only one day after owning the trailer. KZ contacted Lippert who eventually said "it's within specs." Typical Lippert response but in this case it has to be KZs fault as they would have specified this particular frame. This frame is only used on one other brand that I know of so far.
As far as the bounce goes, now you can see what the frame is adding to that. And you should be able to see why the aluminum framing can crack.
KZ has said that they will take care of this problem but 3 months later, we have no idea exactly what is going to happen. Just lots of "we're still waiting to hear".