Thanks for asking this As a new owner of a K75 I've been wondering the same thing, but I've had many other things to worry about first.
Speaking of luggage...
I have been thinking...
Is there some sort of BMW Luggage FAQ somewhere? If not, could there be?
I've read though FAQs and master thread lists here and elsewhere, and that's one topic I've not seen.
I am new and would be of no help in making one, but I know what questions I've thought about:
I know there are different types or styles of tragkorbs, but how many, what is the difference, and how much does it matter? Pictures would of course be a big help here.
Dimensions would help me also. I'll see a certain tragkorb is X litres or cubic inches in size, but sometimes knowing approximate internal length/depth/width is invaluable.
I've read enough to know some latches are a problem. Which ones? Or all of them? Are there good fixes?
Top boxes: What is/was available there? What mounts on what rack?
Is any of this still made? What is still made that woks?
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I don't mean to be looking for work for someone else, but if anyone knows what's what and is looking for a way to battle the boredom of long winter nights, maybe they could help us less fortunate (more ignorant) with some enlightenment.