Those are some really weird results.
What you call a pilot is sometimes called a mandrel, if we are talking about the same thing.
My guess is that tube is heat treated.
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I don’t generally bend tubes outside of a pretty safe range so I am not an expert but there are rules about how much you can bend a tube based on diameter, radius and wall thickness and you’ve exceeded those rules. The center line of the radius of the bend needs to be 3x the diameter of the tube. This would mean whatever you’re bending the tube around needs to be at least 125mm radius.
Keep in mind, those are not hard and fast rules, just rules of thumb, and they are usually skirted via mandrel bending processes, as (I think?) was used here.
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I built a steel front triangle that used a 44.45mm X0.9mm downtube, it had a bend in it that was about 25 degrees on I think a 7" CLR.
the local bending wizard was pretty weary of taking it on because he didn’t like the wallthickness- OD ratio being so extreme.
it cracked or wrinkled on a draw bender despite his best efforts, he ended up filling the tube with cerrobend (spelling?) and working it back and forth on a section roller. wasn’t /perfectly/ smooth but looks perfectly fine under a 2-layer powder.
he said “never again” like it was a bit of a nightmare, but I think he’d be up for it.
best pic thats coming to hand is here.
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