Hi. I've always wondered, if you're "down under" what's that make where I live? Just curious.
Ah, yes, your question. FYIW. First, I'm not a real technical or engineering type guy, but can share my thoughts on the matter. I don't think it's a problem, or at least it hasn't bitten me yet. I have had 3 ST1300s ('07, '08, '10) with approx. 50K, 100k, and 100k miles racked up on them. I never had a pillion rider, but always had both hard side bags, a top box (first a Givi V46, then Pelican Case 1040) AND an aux fuel tank mounted under the Pelican top box. Never had a problem.
Looking at the many stickers that came with each new bike, including my current one, this FJR, all the manuf. recommended weight limits are REALLY low. On the ST, the weight label for the side bags was 20# each and the rear deck is only 10#. I just looked up the limits on the FJR and . . . WOW: Rear Deck - 7#. More important possibly are the Max Loads: ST 459#; FJR 472#.
I'm unaware of anyone having a structural failure due to load position and weight issues. In general I've made an assumption that these limits are a liability and legal issue to take manufacturers off the hook for any problem which might occur and not based on actual material strength limitations. Maybe I'm right . . . maybe Im not.
Anyone else have information to add? Feel free to chime in for all our benefit.
Sorry I don't have a more definitive answer Aussieboy.
Shuey