Triangular frame tubing?

[Funky Monk]

I know this might sound silly to you e-engineers, but I've been wondering this one thing.

Since triangles seem to kick all sorts of arse in terms of structural strength (prob. not the correct term), why aren't bicycle tubes simply made this way? I mean, tubes could be hydroformed, or in the case of carbon fibre, somehow molded into a triangular shape, resulting in a theoratically stronger tube.

I know there's probably some simple reason preventing it, but I just can't figure it out.

[sanjuro]

I know this might sound silly to you e-engineers, but I've been wondering this one thing.

Since triangles seem to kick all sorts of arse in terms of structural strength (prob. not the correct term), why aren't bicycle tubes simply made this way? I mean, tubes could be hydroformed, or in the case of carbon fibre, somehow molded into a triangular shape, resulting in a theoratically stronger tube.

I know there's probably some simple reason preventing it, but I just can't figure it out.

"And we use round tubes rather than multisided tubes, because a tube of three sides or more would need to be heavier than a round tube to provide equal stiffness."

http://www.sevencycles.com/building/materialstechnology.html

[Funky Monk]

But if the weight of the tubeset wasn't too big of an issue, like in dh/fr frames? Would there be any advantages at all compared to a round one? First thing that comes to mind is maybe an improved resistance against big outside forces on small area (hits on sharp rocks etc.). Or would a tube with a thicker wall strength simply do the thing, in addition to saving weight?

This is all very uninformed e-speculation, so if anyone "in the know" would be kind enough to hit me with some hard facts, cool.

[binary visions]

But if the weight of the tubeset wasn't too big of an issue, like in dh/fr frames? Would there be any advantages at all compared to a round one? First thing that comes to mind is maybe an improved resistance against big outside forces on small area (hits on sharp rocks etc.). Or would a tube with a thicker wall strength simply do the thing, in addition to saving weight?

This is all very uninformed e-speculation, so if anyone "in the know" would be kind enough to hit me with some hard facts, cool.
What makes you think weight isn't a big issue on a DH/FR frame?

Frame weight is a huge deal for all bike frames. We are, after all, just puny humans pedalling these frames around. Even for DH, you don't see frames ranging much over the 10-14lb. range, and at the upper end of that range, everyone bashes them for being so heavy.

[Funky Monk]

Allow me to rephrase.

It's an issue of course, but maybe not just as big one as in, say road bike frames. I'm just wondering how much heavier would an optimized triangular tubeset aimed at the dh/fr market end up being compared to the current leading tubesets. And that could the weight penalty be justified by the possible subsequent improvents in strength or other areas.

And most importantly, basically I'm trying find out whether there even are any kind of structural improvements over the traditional round tubes. It'd just make my kind of sense.

Opinions greatly appreciated!

[maxyedor]

actaly the shaped tube-sets are not always heavier than round ones in fact allot of them are lighter, not to put down seven here but the reason they don't use shaped tubes is that they lack the ability to make them, litespeed is the only company doing shaped ti tubesets and incidentaly makes the worlds lighters frame, wich is made without a single round tube on it. The thing to remember is that a triangle is not always the best shape for the aplication as is suffers nearly the same downfall as the round tube in that it flexes equaly in three direction, (as aposed to the round tube wich flexes equaly in all directions) the frame manufacturer will us speciffic shapes of tubes to manipulate the ride quality of the frame, for instance the seat-stays they are generaly designed to flex up and down and not side to side, the other way to use shaped tubes is most common in road and xc bikes, they are shaped to reduce weight, this meads that in the example of the seat-stay you would ovalize the tube sou a smaller tube can be used to give the same amount of rigidity as the larger round tube, smaller=lighter. To answer your question Marin actualy uses triangular stays on their hardtales. so they are out there but there are so many shapes out there with so many different characteristics that to try to define one shape as being the best is simply impossible, next time you are at your lbs take a look at all the different shapes of tubes on all of the bikes, you will be astonished, and probably see a triangle or two

[Funky Monk]

Ok thanks, that answers a lot of my questions, but at the same time awakes so many new ones...hmm...

I read bruefly the series of articles "Metallurgy for Cyclists" written by Scot Nicol of Ibis and some stuff written by Odyssey's George French. I feel a lot a more educated on the subject. I'll have to read them again a couple of times though before I can understand them thoroughly...

[sanjuro]

actaly the shaped tube-sets are not always heavier than round ones in fact allot of them are lighter, not to put down seven here but the reason they don't use shaped tubes is that they lack the ability to make them, litespeed is the only company doing shaped ti tubesets and incidentaly makes the worlds lighters frame, wich is made without a single round tube on it. The thing to remember is that a triangle is not always the best shape for the aplication as is suffers nearly the same downfall as the round tube in that it flexes equaly in three direction, (as aposed to the round tube wich flexes equaly in all directions) the frame manufacturer will us speciffic shapes of tubes to manipulate the ride quality of the frame, for instance the seat-stays they are generaly designed to flex up and down and not side to side, the other way to use shaped tubes is most common in road and xc bikes, they are shaped to reduce weight, this meads that in the example of the seat-stay you would ovalize the tube sou a smaller tube can be used to give the same amount of rigidity as the larger round tube, smaller=lighter. To answer your question Marin actualy uses triangular stays on their hardtales. so they are out there but there are so many shapes out there with so many different characteristics that to try to define one shape as being the best is simply impossible, next time you are at your lbs take a look at all the different shapes of tubes on all of the bikes, you will be astonished, and probably see a triangle or two

That is always a good debate between seamless round tubes vs seamed shaped tubes. I cannot say, although I will BS it during a Seven sale.

[sanjuro]

actaly the shaped tube-sets are not always heavier than round ones in fact allot of them are lighter, not to put down seven here but the reason they don't use shaped tubes is that they lack the ability to make them, litespeed is the only company doing shaped ti tubesets and incidentaly makes the worlds lighters frame, wich is made without a single round tube on it. The thing to remember is that a triangle is not always the best shape for the aplication as is suffers nearly the same downfall as the round tube in that it flexes equaly in three direction, (as aposed to the round tube wich flexes equaly in all directions) the frame manufacturer will us speciffic shapes of tubes to manipulate the ride quality of the frame, for instance the seat-stays they are generaly designed to flex up and down and not side to side, the other way to use shaped tubes is most common in road and xc bikes, they are shaped to reduce weight, this meads that in the example of the seat-stay you would ovalize the tube sou a smaller tube can be used to give the same amount of rigidity as the larger round tube, smaller=lighter. To answer your question Marin actualy uses triangular stays on their hardtales. so they are out there but there are so many shapes out there with so many different characteristics that to try to define one shape as being the best is simply impossible, next time you are at your lbs take a look at all the different shapes of tubes on all of the bikes, you will be astonished, and probably see a triangle or two

That is always a good debate between seamless round tubes vs seamed shaped tubes. I cannot say, although I will BS it during a Seven sale.

However, Litespeed's lightest bike, the Ghisallo, only uses round tubes. The Vortex, their stiffer bike, uses shaped tubes.

http://www.litespeed.com/images/2005/ghisallo_img.jpg

[maxyedor]

I was refering to the new Ghisallo, it even takes a special oval front der. mount. Why they didn't use a braze-on I have no idea. check out there new site. but Moots makes the best imo, mabye not the lightest ti frames out there with round tubes. It's realy just a matter of does it ride well? Does it weigh a good amount? Is it sellable?

[Spokompton]

The only way to get a shaped tube stronger than a round one is if it's made like that from the start. Weight being equal. Obviously a 8 pound shaped frame will be stronger than a 4 pound round one.

Shaping is usually done my bending the metal. As we all know, any time you bend metal it becomes weaker.

There's also the issue of denting. A flat surface is easier to dent than a round one.


If anything, shaped tubes look cooler!:p