dabac

Here we go, another design student dreaming something up while being almost entirely clueless about the subject:"There are no external brakes... Peleg says that he sees such matters being handled in a similar way to the way BMX hub braking operates - when a rider pedals backwards, the bike comes to a halt."

Coaster brake anyone? And when did you see that lately on any BMX intended for serious use?

And then there's this:"The uncomfortable-looking saddle would be made in different sizes to suit different riders and, like much of the design, would snap into place."

So, assuming the saddle also includes the same-coloured bracket that attaches it to the frame, all in one piece - how many different saddles would a seller be forced to stock in order to offer a decent level of adjustability? 10? 20?

For anyone interested, do a net search for "itera plastic bike". Apart from starting from recycled plastic, that bike has already been made. Admittedly, what really killed that one was probably poor business decisions, but it wasn't a very good bike even at the best of times.

Carbonfiberboy 

FEA works, however the problem is deciding what forces to input. It's too hard to model. Hence bikes with metal tubes are mostly built by rule of thumb, developed over time. Shaped tubes are modeled with FEA, but tested by humans, then modified further. Same with carbon bikes, but they're easier. They're modeled with FEA, built, ridden, and then material is added or subtracted to that same frame until the rider/engineer decides that's right. Then they mold another frame with that layup and ride it again.

fietsbob

If it really Matters a Lot,
.. maybe you can do a post graduate degree in engineering, materials analysis,
and write a Masters Thesis on this ?

maybe someone at MIT or Cal Tech has done that, IDK.

then a link to that Publication can be found..

acidfast7

Rear pegs, still good for people transport if you don't have a rack.

Crotch mold, 3D scan, 3D print ... seems pretty easy.

Darth_Firebolt

just curious, but what do you think the FEA program is doing, voodoo? it's all math. if you do it by hand; it's math. if you model it in a computer and hit run; the computer is still doing math.

garage sale GT

Actually, it models highly complex geometry as a series of simplifications and then solves thousands and thousands of interrelated equations. No way a person could do all that. Not enough time, no chalkboard or paper big enough to keep track of all the equations.

garage sale GT

I think they can do pretty good with FEA. They can't model the real world but then again if something really wierd and extreme happens to your bike, you're likely not to hold it against the manufacturer. You probably can't sue.

Steel frames have been developed with tradition born of long experience, but it's a working method. Plus, people expect and accept tradition in a steel frame.

Burton

Yup - had one of those come in the shop last year. Still completely functional - outlasted the company! It was unusual unough that I took pictures - later in the week I'll see about uploading something.

Airburst

Solving a load of interrelated equations isn't maths?

OK, it's an approximation, but it's still maths.

HillRider

Correct but isn't that why we have computers? There are a huge number of mathematical techniques that are completely impractical to do manually but take only seconds with a computer. FEA is one of those techniques.

Back in the '60's I recall a camera lens manufacturer designing a very complex zoom lens using a laborious but very accurate "ray tracing" technique that they estimated would have taken 20,000 people, 20,000 years to do manually but took only a weekend using the computers of the time. These days it probably would take less than a minute.

garage sale GT

We don't have the math to model complex shapes precisely.

FEA programs simulate a complex shape as an interconnected lattice of many, many simple members.

If you want it to be a reasonable approximation you often have to make the mesh so fine that it would not be humanly possible to solve all the equations.

So we can't solve it with math. We can approximate it with simplifications, but there is so much math it would take forever.

Airburst

OK, we can't solve it precisely with maths, the point is, we can come up with a decent approximation using maths.

Bike Gremlin

garage sale GT

I think it's more pertinent to ask whether there's a test that gives a real world result which translates into whether a bike has a good ride or how much the flex affects steering or power transfer.

They have tested a few frames for millimeters of flex under laboratory conditions but even if every frame came with a table of flex values it would still mean very little.

I don't think there is such a real world test save for subjective analysis by bike authors.

The original jerkoff's question doesn't have much point.

FBinNY 

The OP asked a simple and IMO legitimate question. He specifically said he wasn't looking to start a debate. I don't think it calls for name calling, especially from someone who seems only interested in prolonging the debate that wasn't called for in the first place.

Of course you'll want to have the last word, and as far as I care, you're welcome to it.

garage sale GT

I can expand on his point.

I can point out that those who live in glass houses shouldn't throw stones.

So there.

dabac

I have no idea how that is meant to tie in to what I wrote.

Oh, sure.
In a world where it's real easy to find shops who won't have tension meters, won't use torque wrenches, won't have loaner programs for finding the right stem length or a suitable saddle - and you think 3d-printers and associated hardware is reasonable to expect?

Now, I'm all for a way of turning recycled plastic into something more useful, but inventing a new, but less adjustable and less compatible way to attach a saddle seems rather pointless. He might as well have gone for a brand new wheel size.

Kimmo

Darth_Firebolt

https://en.wikipedia.org/wiki/Finite_element_method

garage sale GT

If every maker tested their frames for how much a standardized load makes the front and rear axle move, and how much a torsional load like standing on one pedal makes the bottom bracket deflect, and how much the bars deflect from a standardized load, then you could compare frames, but only if the test was standard.

FBinNY 

All that might be somewhat helpful, but it'll never happen. In any case you'd still end up with apples and oranges comparisons. Ie, one has a stiffer BB/seattube, the other less head twist in hard cornering. Given all the variables involved, the only meaningful test for frames or bikes remains a real world road test. There are just too many variables, not the least of which is the engine/payload.

acidfast7

I'm not sure where you live, but bike mechanics make 30-50€/hr and we use the tools to ensure that everything is within proper specs. There's also no drop-in service here, per-arranged appointments are mandatory.

3alarmer 

I have theorized that it is impossible to bring up the topic of
frame materials on Bike Forum without starting a rather acrimonious
and often ill informed debate.

As another point of experimental data, this thread brings me that
much closer to scientifically publishable results. Thanks to OP and
all participants...............kudos

3alarmer 

I know it's hard to believe, but there are many differences between
Germany and the USofA. Prevailing wage scales for bike mechanics
is only one of them.

garage sale GT

Another reason it would never happen is manufacturers would have to get sharper. Anyone could see that a larger frame or a wider bar was flexier than a small one...and they'd demand the manufacturer use a different tubing for each size....even if sometimes it's not an important difference.