Hot answers tagged luggage
I would suggest splitting the weight in half and putting it low on your bike for stability. Here is my daily commuting configuration (2 matched 6 gallon plastic waste baskets mounted by hose clamps to a standard bike rack.) (Your emptied backpack could be rolled up and placed on top if you need it for off-bike use.)
This is more of an extended comment. If you're mounting it on one side, that's likely to be quite a lot of weight off-centre, which will also affect the handling. I'd aim for vertical, but you'll need something solid underneath to support the weight - like 2/3 of another rack inverted and bolted/clamped to your rack. Alternatively you might get this to ...
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