Concept Bikes & Bike Innovation - for better or worse

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lae in reply to @TRA

Although when I mentioned stamped out box sections I probably should have elaborated. In my head I was thinking of fancy hydro-formed shapes with engineered flex/stiffness etc and different wall thickness at any given point. I'd assumed that's where the ductility comes into it?

Trek (I think) made a DH frame out of two halves welded together, a few years ago now. It was aluminium though.

How oversized do you want to go? you get something which has to be handled with care to avoid dents.

Well that's the beauty of greater specific strength. You can have an oversized tube with greater wall thickness for the same weight. Or the same tube geometry for less weight. Or any compromise thereof.

I'm not sure that yield strength is the limiting factor for chains... At some point, elastic extension

Uh huh, fair enough, maybe elastic deformation is a limiting factor in power transmission for sprinters, maybe yield strength and therefore weight is a limiting factor for climbers. My point was that saying 'strength is never a limiting factor' was rather glib of you, without having defined 'strength' or 'limiting factor'.

I rode one of these last season, it was great fun. Only goes downhill though.

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gbj_tester in reply to @lae

You can have an oversized tube with greater wall thickness for the same weight.

Only if the density changes. We're talking about steel here, for most purposes we can treat the density as invariant for all steels, nearly all of them are between 7.7 and 7.9 and even an exotic alloy like AL6XN which is <50% Fe is only 8.1

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lae in reply to @gbj_tester

But the density does change. That's the whole point! Read the Nature article.

The reason the densities of your quoted steels are in a narrow range is simply because the other metals its alloyed with have similar density (chromium, nickel, etc). The steel in question is alloyed with aluminium - steel's density is 8g/cm3, alu's is 2.5g/cm3. Presumably the interest from the auto and steel industries informs us that the density change is significant.

Your other comments regarding strength... I can't really be bothered to get into it, but there's no such thing as a 'normal' definition of strength. There are probably a dozen common attributes which could be referred to as strength, and probably a dozen more esoteric ones that neither of us could define; your point is just too generalised to be applicable or meaningful for every single chain link, sprocket, bearing, axle, bolt, or even frame. We'll just have to agree to disagree on this one.

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