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Thinking about what @jj72 said, I have seen some incredibly large people riding bike-shaped-objects, but never something of quality. I’d question whether quality is synonymous with strength.
I know that it’s a pretty lame example but I’d consider it as cheap denim vs silk. Are there really low end components that are heavy and overbuilt that will withstand greater abuse than high end?
I’d expect Thomson et al to break, because I envisage they shave grams off to keep performance high, as their range of users is 10st lighter than you’re thinking, but they maybe have a grey area of avoid-lawsuit-strength.
Maybe the engineers will get angry with this, but if bike/component weight isn’t the issue, then are steel/heavy components going to have a lower risk of catastrophic failure at the extreme end? I’m thinking a thick walled steel seat tube will be better than alloy?
pdlouche-
Maybe the engineers will get angry
Not angry, but they will want to add a caveat. There's more to strength than just how much metal you use. Taking just the typical steels used for seat tubes, a BSO made from mild steel will need to be more twice the weight of a good 4130 frame just to have the same strength.
gbj_tester
That reference is useful and as I thought - and slightly unnerving -being my Bro is closer to 25st. Perhaps first step is literally dig out the shed/get a beater frame/bike and stick some 36H on it where the financial risk is negligible and hope, if he enjoys ,and benefits from, it he'll look to invest time/money in getting something he'll use little and often