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Never had a problem whilst carrying on my back, then I get a front rack (front axle to handlebars type), attach it to bike with 25c tires, and withing two months elements I had to repair my f2.8 70-200mm & f2.8 17-35mm, two heavy lenses with lots of elements. You can imagine how expensive that was. Too many bumps and vibrations from the road. Start carrying on my back again, no problem. If you are carrying kit on a rack I'd be careful.
photoben-
Thats such a bummer! I have a couple of heavy glasses (wides, no teles) and I really abuse the crap out of my gear. Never had such a problem. Maybe the orientation of the lens would make a diff? If I had the opportunity I would probably make sure the lenses were stored and transported 'upright', apertures closed, zoomed out, and packed tightly in the cases to stop them rattling.
Then again I could just get a sick elastomer rack! Have you patented this idea? You should at least name it.
Kidneys
Loved this. The paint is rad, too.
But i'd be a bit concerned if the elements in my lenses could 'shake loose'.. shocked emoji