Originally Posted by
fietsbob
I expect you need stiffeners on both sides so it wont bulge outward requiring a Bowlegged pedaling technique.
No.
Unless you have a freakishly narrow Q, which isn't common on typical off the shelf bikes these days, or have some weird leg geometry.
I can stuff my bag full of a hydro bladder, clothes, tools, etc... never give it a though.
Only time I brush the sides is when I stop and keep a leg over the bike clipped in and I stand at a light or to chat... otherwise, it doesn't happen with all the typical bags I've used.