It's like carrying a stage cylinder in backmount twins or even in sidemount, you very quickly adjust to it. It's tucked up so close to your body (or at least should be), that you don't have a huge amount of roll, and because most SM wings pull around the body, balance is very easily maintained. In a Hogarthian style SM harness you really only need to add a couple of KG of lead to offset only carrying one tank now too.

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Air is for pussies.