Concept Bikes & Bike Innovation - for better or worse

Probably all true, people love to special. (Ti jewellery bikes etc.)

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?

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?

Those things are possible now with aluminium. Kinesis even do superplastic forming on some frames. The advantage of that Flash steel would be that there is no heat treatment needed after forming, but I don't think that's a huge part of the cost on aluminium frames anyway.

fun, until you want to go uphill out of the saddle...

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.

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

My point was that saying 'strength is never a limiting factor' was rather glib of you, without having defined 'strength' or 'limiting factor'

For almost any normal definitions of both "strength" and "limiting factor", my point substantially stands. The spokes in very low spoke count wheels are probably the closest thing we have on a bike to a piece of steel which is only just strong enough, and even there the limit seems to be that the wheel gets too flexy if we cut the total spoke cross section even further.

maybe elastic deformation is a limiting factor in power transmission for sprinters, maybe yield strength and therefore weight is a limiting factor for climbers

Depends...

Road sprinter, 1500W, 53T chainring, 110rpm, chain tension 1200N
Climber grinding up Angliru, 500W, 34T chainring, 70rpm, chain tension 990N

Not much in it

It's electrically assisted.

Uphill fun too.

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.

The first rule of metallurgy club is, you don't talk about metallurgy club.
The second rule of metallurgy club is, you don't talk about metallurgy club!

@hippy has a met-allergy

But the density does change

I thought we were still talking about Flash Bainite, which is heat treated ordinary steel.

If you actually read all the way to the bottom of the nature article about the Al-containing alloy we were discussing earlier, you'll find that the density is about 6.8, usefully lower than ordinary steel if you're a car maker and you can directly substitute in the same section thickness as you could knock over 100kg off the vehicle weight for every tonne substituted, but not exactly a game changer for bicycles. The few bicycles where weight is a primary concern typically contain less than 1kg total steel, and as that is all in the chain, spokes, wires, fasteners and bearings, none of which is likely to be a targets for a low density alloy steel, I can't the bicycle industry taking any interest.

steel's density is 8g/cm3, alu's is 2.5g/cm3

I hope you're not suggesting that you can guess the density of an alloy from the composition :-) The density of the 15% Al steel under discussion actually comes out a bit lower than the figure you'd get from simply guessing that the total volume of the alloy would be the total volume of the unalloyed components.

http://www.bikeradar.com/road/news/article/3d-printed-36-28-postale-concept-bike-has-mismatched-wheels-and-unusual-geometry-46065/

Posted? https://www.youtube.com/watch?v=qLeOqoS0gHc

Why add a new heavy and complex direct drive to the front when you already have one set up at the back?

see also: e-bikes

Sure but imo either you get just some kind of inertial drive to the front or if you're going direct you might as well intervene on or replace the existing drivetrain at the rear.

I am also not sure if it provides any benefit.

I just post shit like this for the ensuing discussion between engineering types.

Don't forget IT HAZ TRI SPOK!

Me too. I like the discussion as well. Btw wouldn't that understeer like crazy and slip uphill? :)

Combine with a Copenhagen Wheel and you've got the ultimate bolt-on 2WD conversion.

So much lolz!

http://www.designboom.com/shop/design/plume-mudguard-plume-12-30-2015/?preview=true&preview_id=16873&preview_nonce=a814f415ba

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