Sounds like I'm not the only one with this problem. without any engineering or fabrication background, other than little stuff here and there, when I look at the AltRider rear rack design, it just looks wimpy to me. Yeh, cool cutouts but I'm not surprised it got beat up given the thickness of the aluminum and placement of the mounting bolts. None of the bolts where loose. I always ride with the top box on, and never put the heavy stuff in there - that goes in the Bumont side cases, which are rock solid. But when I have some stuff in the top box, it naturally get bounced around as I go over bumps. Hence, the box is always slightly flexing back and forth, up and down. Always. It's unavoidable, especially how it's positioned up high on the end of the bike.
The first sign of stress failure I saw was at the more centrally located, rear pair of bottom bolts. They're basically in the middle of the bottom plate, as highlighted in the below pic. So what happened naturally? The plate started bending near those, bowing down towards the edges. You can see the stress cracks right at those holes in my initial pics. I was worried about that, but didn't pay attention until I could move around my top box too easily during a quick check before a ride. Took a closer look, and I shared earlier what I saw - a totally failed bottom plate.
I wrote AltRider, asking if I could purchase just the bottom plate. I'll see what comes of that, but am not hopeful given other comments here.
Bottom line - anyone with an AltRider rear rack for a top box I'd suggest reinforcing it (multiple ways to do this) before this happens to you. Seems like a virtual inevitability if someone rides over anything but highway smooth rodes. Maybe I'll try to gerry-rig my own bottom plate with the tools I have. Might not be pretty, but that's the least of my concerns for a part like that.
