Helix shaped tubes?

[gjenkins@]

Originally Posted by cannonballtrail

My Pro 29er cracked along the helix and they fixed it under warranty. Great customer service and this is by far the best bike I have ever owned or ridden, but yes, even I must ask, what's the point? Well, the idea is over 100 years in the making.

http://www.theoldbicycleshowroom.co....cle-1510-p.asp

On a more serious note, I don't understand "Looking at tubing cross-sections in CAD drawings, it became apparent." This was determined by "looking at" just as Einstein "looked at" a clock tower and came up with relativity, I guess. A giant leap for mankind from the boys at Lynskey? What happened to a finite element analysis of bending moments, torsional rigidity, compression, and tension? Test results? Their write up either doesn't want to give away trade secrets and RD or they're just spewing hot ti. Whatever the case might be, the design looks cool and the bike is a blast to ride.

I am contemplating a Ti Lynskey or Vassago this next summer. I am open to new tech and will wait to hear more reviews from people who know what they are talking about before I make a decision on this. Owner reviews (such as yours) and technical analysis basically.

[Climber999]

Originally Posted by JohnnieA

I think that if helix was stronger than round, tree limbs would be helix shaped. Trust mother nature.

I am afraid you rely incorrectly on the principle of natural selection. Mother nature improves things when there is pressure to change; utmost rigidity and resistance to torsional pressures have not been trees top priorities.

Anyways, Lynskey has an identical model--dimension wise--which Ted Guitar tested and pointed out to flex in the frame. From personal experience, the Pro29 2010 does not show a hint of flex whatsoever. Now, I may not be as heavy or strong and Ted, so it would be interesting to have him test that bike as well.

[pvd]

Originally Posted by Climber999

...Mother nature improves things when there is pressure to change; utmost rigidity and resistance to torsional pressures have not been trees top priorities. ...the Pro29 2010 does not show a hint of flex whatsoever.

That sounds like a really bad bike.

Any road or mountain bike needs to be designed to have just the right amount of flex in just the right ways. A mountain bike that doesn't flex will not track well in corners at speed. A road bike won't hug the road quite as well without some flex. The only bike that really shouldn't be flexing is a velodrome bike.

Motorcycle companies put massive amounts of time and energy into making sure their chassis flex properly. They stopped making hyper-rigid chassis about 20 years ago.

Basically, bicycles ARE just like trees. They flex to survive.

[unterhausen]

even if the objective was to avoid flex, given the same amount of material and any choice of shape possible, a helix really seems unlikely as a shape that would win out as the stiffest tube. I think our intuition incorrectly takes work hardening into account into our mental calculations of stiffness. Anyone that has bent a paperclip to failure feels the clip becoming harder to bend as it becomes work hardened. But that is outside the elastic limit of the material, something you don't experience with a bike that is going to last until the next ride.

[coconinocycles]

i'm working on the "moebius" frame - it's all mine & it's going to be 15263% stiffer then anything you guys have ever seen. heads up. Steve Garro, Coconino Cycles.

[Schmitty]

Originally Posted by cannonballtrail

Well, the idea is over 100 years in the making.

http://www.theoldbicycleshowroom.co....cle-1510-p.asp

You got the translation wrong on this. Should read: "Very few 'new' marketing gimics are new. Most have been tried, and few have stood the test of time".

All those tubes will break b/c forming them into that shape has already broken them most of the way. Out of S3? What a joke.

-Schmitty-

Actually, the bike in that link has round tubes with helical seams ala cardboard toilet paper roll. Different deal.

[dbohemian]

Just because I was curious.

I modeled two tubes. Made it real simple and FEA is only as good as the info in and this is a simple beam bending example. Not very fancy.

One was a .6 wall 1.5 tube round and the other was a helix tube same size, same thickness.

I applied a 100lb load in one direction while fixing one end. Tubes weigh the same within a few grams.

Bottom line as far as displacement is concerned. Round tube flexes 12.35mm and helical tube flexes 15.08mm. Helical tube is not as stiff as a round tube. At least in pure sideways loading. I also ran some torsional scenarios. Round tube is stiffer again by a fair amount and overall peak stresses are less for the round tube.

The helix tube began to show points of failure at 1.5 times a factor of safety and the round at 1.75. The round tube is superior here also.

I would say though, taking a queue from Mythbusters........This myth is BUSTED....

[swift]

...But you're modelling a hexagon tube vs. the original square.

The stress concentrated on the apex of the corner is what I would have expected. Good illustration.

The springer fork on that Indian Larry chopper is sweet!

[dbohemian]

Originally Posted by swift

...But you're modelling a hexagon tube vs. the original square.

The stress concentrated on the apex of the corner is what I would have expected. Good illustration.

The springer fork on that Indian Larry chopper is sweet!

Opps. Well, I changed it to a square of equal weight. The deflection got even higher and stresses are greater still. Really busted.

One of use should make a springer with chain

[Walt]

Look at the big brain on Brad! Er, I mean Dave.

BTW, we will see you in like 3 weeks. Be ready for some mountain biking and beers...

-W

Originally Posted by dbohemian

Just because I was curious.

[aosty]

Originally Posted by swift

...But you're modelling a hexagon tube vs. the original square.

Look at his pic again... it's actually pentagonal...


@bohm - Nice job!

[shiggy]

Originally Posted by coconinocycles

i'm working on the "moebius" frame - it's all mine & it's going to be 15263% stiffer then anything you guys have ever seen. heads up. Steve Garro, Coconino Cycles.

That will be the perfect bike for my "Escher" trail! An all downhill loop.

[unterhausen]

Originally Posted by coconinocycles

i'm working on the "moebius" frame - it's all mine & it's going to be 15263% stiffer then anything you guys have ever seen. heads up. Steve Garro, Coconino Cycles.

my lawyers tell me it's safe to reveal that I have applied for a patent for bicycle tubes based on the Klein bottle and all other higher dimensional manifolds with a non-intersecting surface. The only problem is that they are really hard to miter and sometimes fatigue cracks start in the higher dimensions and you can't see them until it's too late. The advantage is that they are optimally horizontally stiff and vertically compliant ... as far as you know.

[dr.welby]

I'm working on a prototype Shroedinger's Frame but I can't find anyone willing to test ride it.

Meanwhile: Quantum Slacks

[unterhausen]

Originally Posted by dr.welby

I'm working on a prototype Shroedinger's Frame but I can't find anyone willing to test ride it.

I dunno, that should be a real hit at Critical Mass

[cannonballtrail]

The thread that doesn't die. Thanks for posting the FEA. I think Lynskey varied the wall thickness, however the point is a Helix has more flex than a round tube regardless. Second, as my materials prof used to say "garbage in garbage out" when it comes computer models vs. in-situ tests, so I think a lab test is in order. Anyone want to sacrifice a Pro 29er?

Well, I just got back from 3 days on the road with my Helix. Tucson Mnt Park, Trail 100, and Coast to Coast on National in PHX + the hill climb and Mormon. The bike is actually quite flexy, but some flex=comfort and control IMHO. At 140 lbs with gear, I might not be the best tester.

Still on a level of strangeness the Pro 29er pales in comparison to the black sheep.

[coconinocycles]

Originally Posted by dr.welby

I'm working on a prototype Shroedinger's Frame but I can't find anyone willing to test ride it.

i bet it kills you like a cat in a box............maybe. + the klein jar comment made me bust up & i feel like crap, so thanks, Ut! Steve Garro, Coconino Cycles.

[surlytman]

I'm surprised Gary Fisher didn't come up with that marketing drivel!

[cannonballtrail]

Just received a mail from Niner with a preview of their Air 9 carbon and what are they advertising? A hexagonal downtube for better "stiffness." Now this is not the same as twisting a tube or plastically deforming a tube and calling it stiffer, but it is interesting that they have departed from the round tube concept. Do they know something we don't?

http://www.ninerbikes.com/fly.aspx?l...ikes&taxid=271

[coconinocycles]

Originally Posted by cannonballtrail

. Do they know something we don't?

nope. it's just that with production units if you don't have a new offering every model year people loose interest. in custom every bike is it's own model...........just sayin - not bagging on niner........... Steve Garro, Coconino Cycles.

[jcrew94123]

While they mention hexagonal, Niner doesn't mention that they twist the downtube - it looks pretty straightforward/symmetrical to me in the pics on their site.

[Schmitty]

[QUOTE=cannonballtrail] Do they know something we don't?

[QUOTE]

They can barely make a frame that doesn't break....

I'd insert a youtube of Steely Dan doing Asia here, but I'm lazy.....

-Schmitty-

[gjenkins@]

Originally Posted by dr.welby

I'm working on a prototype Shroedinger's Frame but I can't find anyone willing to test ride it.

Meanwhile: Quantum Slacks

Are you kidding? Huckin Kitty is both riding it and not riding it as we speak.

[vulture]

I wonder if the direction of the twist is specific to the northern hemisphere? I mean whats that thing gonna ride like if it conflicts with the Coriolis force when it is in say, New Zealand or some other southern hemisphere location? I love the bike industry.

[shovelon]

Originally Posted by vulture

I wonder if the direction of the twist is specific to the northern hemisphere? I mean whats that thing gonna ride like if it conflicts with the Coriolis force when it is in say, New Zealand or some other southern hemisphere location? I love the bike industry.

My Karma hates your Voodoo.