Aerodynamics. That slight movement as air passes over prevents that from being transmitted to the bike chassis at higher speeds, resulting in potential death wobble.

 

I just installed mine and all the back-and-forth sliding is in the mounting plate. It's clearly the design intent as there are slots and elongated plastic bushings that enable it to slide left/right. I've never encountered this in the past on other bikes I've owned but this is definitely how it's supposed to work.

 

I think Truimph came up with this floating luggage mounts first, I could be wrong? Harley out sourced the panniers to SW Motec and they know their onions. I still find Givi hard to beat for longevity.

 

I had the same issue, but after the base plate recall this is resolved now. It seems they have used different washers this time.

 

Don't suppose you could get any information about that recall? Mine slides back and forth and I got my PA well after your post. I purchased it last June and had the hd brand aluminum luggage installed. I've recently been noticing some noises and it turned out that some bumps were causing the trunk to slide around and make noise. I went to go and tighten the bolts and noticed it seems intended to slide around complete with softer parts so that it can do this. Maybe they wanted it to keep stuff in the top trunk from taking too much vibration, but I doubt that really affects much?

 

Here's the recall notice. It had to do with the screws that held the seat base in. I had my recall done and my top box is still sliding. The recall did not have anything to do with the top box mounting system.

https://static.nhtsa.gov/odi/rcl/2021/RCRIT-21V924-0263.pdf

 

That recall was for the handrail screws not for the mounting plate. Haven't heard of a recall dealing with the Base plate for the top box. As others have posted, it's designed to have some play.

 

Seems clear it's intentionally designed that way--although it's not clear why. Discovered the same thing last night while washing my bike and attempted to tighten the plate down--but it still slides. Underneath, it's clearly an adjustable slide and on top it uses a plastic washer under a steel washer.

 

It’s by design. In the installation guide, the washers are specifically listed as “sliders,” which allow the box to move with the wind when riding. It seems like overkill but it is still neat.

 

The slide is supposed to aid aerodynamics at speed. It is in the design.