# Frame design aka Black Sheep



## gsomtb (Jul 18, 2007)

Can you guys please explain to me the reasons for using the extra tube b/t the top/down tubes on Retrotecs and Black Sheeps?

Thanks....I'm intrigued by these....


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## scooter916 (Jan 2, 2006)

Simply because they look badass, it reminds us of the balloon tired schwinn cruiser none of us cold afford when we were younger


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## Walt (Jan 23, 2004)

*Just for looks.*

AFAIK, they are just to look neat.

-Walt


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## gsomtb (Jul 18, 2007)

Thanks for the replies guys.
They ARE easy on the eyes.

Walt, your stuf is classic. Keep up the good work....


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## pvd (Jan 4, 2006)

Pure fashion, no function.


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## Live Wire (Aug 27, 2007)

pvd said:


> Pure fashion, no function.


The funniest thing about the kicker tubes is that they were originally put there to mimic the motorcycles of the day (think Excelsior project) to help sell bikes to kids.
FWIW, I think they look cool as hell....got a double tt 29er in the jig as we speak!:thumbsup:


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## Walt (Jan 23, 2004)

*Yep.*

Same story for the insanely expensive truss forks that some folks swear by - that design was originally intended to help bike sales by imitating the look of 30's era motos for kids bikes.

-Walt



Live Wire said:


> The funniest thing about the kicker tubes is that they were originally put there to mimic the motorcycles of the day (think Excelsior project) to help sell bikes to kids.
> FWIW, I think they look cool as hell....got a double tt 29er in the jig as we speak!:thumbsup:


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## Francis Buxton (Apr 2, 2004)

I can see a little bit of function in a truss-style fork. Truss style forks generally utilize a smaller diameter blade (relative to standard straight bladed forks), and they are usually curved, which has some effect on where the deflection in the fork occurs. Many often have a greater than 'standard' offset also. Taking those points into consideration, the 'base' fork would naturally flex a little more than your typical unicrown style forks. Many forks can end up producing some vibration in rougher terrain. If you add a smaller diameter truss tube extending up into the head tube area, I think you can 'accidentally' provide some vibration damping while you are adding a small amount of support to the smaller-diameter fork blades. The truss tubes are a smaller diameter and different thickness, meaning that they should harmonize at a different frequency than the fork blades. If you get it right, the two pairings could work together to dampen the vibration out faster than the fork blades alone.

And I think they look cool.


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## brant (Jan 6, 2004)

Francis Buxton said:


> If you get it right, the two pairings could work together to dampen the vibration out faster than the fork blades alone.


Ah - that's it, is it?

OK - what would happen if you got it wrong?


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## Francis Buxton (Apr 2, 2004)

Well, based on the physics classes I took long ago, the two pairs could harmonize together and make it worse....

I really haven't spent any time working on analysis, more just 'what if' thinkering inside my head.

I do think that there is more functionality to a truss fork than there is to the 'sex tube' that James uses or the extra horizontal tube in many cruiser frames. If you design a truss fork correctly, the main fork blades should be smaller than you would normally use for a similar non-trussed fork, which is what McClung, James, etc. appear to generally do. It's on my list of things I want to build to test it out for myself, but I'm just not there yet.


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## dr.welby (Jan 6, 2004)

[email protected] said:


> OK - what would happen if you got it wrong?


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## pvd (Jan 4, 2006)

Francis Buxton said:


> I can see a little bit of function in a truss-style fork. Truss style forks generally utilize a smaller diameter blade (relative to standard straight bladed forks), and they are usually curved, which has some effect on where the deflection in the fork occurs. Many often have a greater than 'standard' offset also. Taking those points into consideration, the 'base' fork would naturally flex a little more than your typical unicrown style forks. Many forks can end up producing some vibration in rougher terrain. If you add a smaller diameter truss tube extending up into the head tube area, I think you can 'accidentally' provide some vibration damping while you are adding a small amount of support to the smaller-diameter fork blades. The truss tubes are a smaller diameter and different thickness, meaning that they should harmonize at a different frequency than the fork blades. If you get it right, the two pairings could work together to dampen the vibration out faster than the fork blades alone.


Nope. It doesn't work like that. Any ridgid fork (passive suspension) will function just like an undamped leaf spring. The structure effects the spring rate, not the damping. A good starting place for thinking about this kind of stuff is by looking at one of Jeff Jones' bikes. Everything is wrong, total bull$****. Take whatever eplaination that is offered about the design and put in you 'Thinks I know are wrong' file.


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## Schmucker (Aug 23, 2007)

Yeah, but you're wrong about a lot of things too, PVD. We just know better than to argue.


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## Thylacine (Feb 29, 2004)

pvd said:


> Nope. It doesn't work like that. Any rigid fork (passive suspension) will function just like an undamped leaf spring. The structure effects the spring rate, not the damping.


100% Correct.

For the record though I think Jeff Jones is trying to build in some vertical compliance *shudder* in the rear of his bikes, but add some stiffness by trussing the fork.

However as per previous posters, the retro styled frames with the dual top tubes do pretty much bugger all except make you look like everyone else who 'emulates' the design.

I guess you could say I'm not a fan


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## pvd (Jan 4, 2006)

Thylacine said:


> For the record though I think Jeff Jones is trying to build in some vertical compliance *shudder* in the rear of his bikes, but add some stiffness by trussing the fork.


Take a close look at one in person. Most of what Jeff does is cosmetic. Take a special note of how and where each tube connects. The same could be accomplished by just using longer seatstays. It's a totally screwed up design fed by leagion of stupid minions. Gotta hate those bikes. They are so lame.


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## pvd (Jan 4, 2006)

Schmucker said:


> Yeah, but you're wrong about a lot of things too, PVD. We just know better than to argue.


I am always open to argument. Stand up and be counted when you think you should. Silence is agreement.


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## coconinocycles (Sep 23, 2006)

since i build "cruiser" style frames, i'll chime in - yes, it is 100% cosmetic, although, the double toptube bikes are pretty stiff...........they sure look cool, though! steve.


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## Francis Buxton (Apr 2, 2004)

pvd said:


> Nope. It doesn't work like that. Any ridgid fork (passive suspension) will function just like an undamped leaf spring. The structure effects the spring rate, not the damping. A good starting place for thinking about this kind of stuff is by looking at one of Jeff Jones' bikes. Everything is wrong, total bull$****. Take whatever eplaination that is offered about the design and put in you 'Thinks I know are wrong' file.


I'm at least somewhat with you on the Jones bikes.

I didn't say that I thought you would get much 'damping' out of the truss, but I do think, as you stated, it adds another dimension to the spring rate. I think a well thought out truss fork can have a purpose to it that is more than simply aesthetic. I will also admit that I think a truss fork starts from the aesthetic and works into a design that accomodates it.

And as much as some might hate to admit it, Peter is right quite a bit of the time, even if his delivery method isn't always popular.


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## dr.welby (Jan 6, 2004)

What puzzles me is why we should accept claims of fork compliance from someone who runs a nearly 4" front tire.

Nice fabrication, though.


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## ted wojcik (Mar 12, 2006)

*The customer decides*

We can comment, argue, and debate all the curved tubes and other trends, but in the end, the customer decides what we build. In the past 10 years the long genesis of material configuration and geometry has been disregarded for fashion based frames. All I can say is, sooner or later common sense will be in style again.


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## byknuts (Aug 9, 2008)

pvd said:


> Nope. It doesn't work like that. Any ridgid fork (passive suspension) will function just like an undamped leaf spring. The structure effects the spring rate, not the damping.


Just like they lay different rate leaf springs atop each other to modify their compression and rebound characteristics a truss fork's two blades (per side) with different angles to disperse the impact force, and tubing diameters can effectively TRY to act as a form of highly primitive damping. 
They also used to use a compressed stack of leather as a spring so it certainly isn't a time period whose technology I'd be trying to emulate.

I'm not saying anyone's particular example actually WORKS (be it bs or jj), or is reliably repeatable from one fork to the next considering the angles of the tubing, bends, welds, etc. all factor in... but the theory's no different than leaf springs...

I feel that proper suspension fork makes more sense either way

Oh, and it's spelled "rigid" not "ridgid", and the structure "affects" not "effects"
(since we're nit-picking)


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## Thylacine (Feb 29, 2004)

It's not 'damping' what you're describing. Don't springs have a frequency, amplitude and duration, and the 'damping' is a deliberate system used to return the spring to a static state? Leaf springs as far as I understand have no damping.


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## dRjOn (Feb 18, 2004)

just out of interest pvd, have you had any time riding a jones frame? serious question, not inflammatory - i saw you at sswc and wondered as there were several jones frames there you could have tried.

i dont doubt your credentials in terms of engineering, but the jones frame is without doubt the most compliant i have ever ridden by a significant amount. i have been lucky enough to have several custom builders produce frames which were designed to be relatively stiff laterally and for the drive chain as i race and ride singlespeed and fixed exclusively, but with additional measures for compliance (super long seat posts with tubing picked to aid comfort for endurance racing) and the jones is in a different league. 

i am not star struck with this, i am fortunate enough to be able to choose pretty much what i want in a frame, and struggle to explain how it can feel so good in terms of intended function if the frame is designed badly - id certainly love to hear more.


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## Thylacine (Feb 29, 2004)

He's not saying it's not compliant. Read his posts again.

He's completely right. If you want to see what he's talking about, look at say a Silk-Ti. If you were to believe in Jeff Jones' methodology - that the seatstays are in bending - the Silk-Ti wouldn't work. The reason the Silk-Ti and other softails work is because the seatstays are predominantly in _compression,_ not bending. So knowing this engineering fact, if you wanted to make a hardtail more 'vertically compliant' (There's half the problem), you allow the seatstays to compress somehow.

It's that simple really.

What Jones should've done is engineered a Monostay style design using some minature leaf springs where the stays meet the mono-tube. *BAM* 10 times the 'vertical compliance' he gets from his current design. (Still no damping, but hey, this is 'pretend suspension' anyway).

That might be low on the sexy-factor though. :idea:


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## brant (Jan 6, 2004)

dRjOn said:


> struggle to explain how it can feel so good in terms of intended function if the frame is designed badly - id certainly love to hear more.


I don't think it's designed "badly" in the sense of the end result that you feel when you ride it. I wouldn't attempt to speak for pvd, but his comment "same could be accomplished by just using longer seatstays."

the "designed badly" (your words) is perhaps that in pvd's eyes (and others), he's solving the problem in a way using a more complex arrangement of metal than others consider necessary.

I know you well enough (drjon) to know that you take an almost empirical approach to your bikes, riding, and your work (natch) - and do believe that you are feeling what you are feeling (and I do mean physically, not just emotionally with the frame).

Personally, I've been thinking of a response to pvd...



pvd said:


> . Most of what Jeff does is cosmetic. Take a special note of how and where each tube connects. The same could be accomplished by just using longer seatstays.


Are you going to go do it? Make a frame with longer seatstays? Test it and see what happens?

I'm still a bit upset that I've not seen any empirical frame testing lately. Rinard did some, and I remember early Bicycling magazine showing "Tarantula" test figures including "splay" (I like splay)...

I might make something up with some weights and clamps and dummy axles and stuff, and throw a few frames in it to see what happens. My FEA is terrible.


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## dRjOn (Feb 18, 2004)

"Gotta hate those bikes. They are so lame."..at the risk of sounding like a cock...i was paraphrasing!

err, but longer stays would longer no? so that would undo one of the design parameters? to have shorter wheelbase and stays...with more weight over the rear axle. if you lengthened the stays, this would mean the use of an even more relaxed seat angle and the headache that would cause in terms of front centre?

thyalcine, when you say 'in bending' etc, do you mean the seat stays are not able to work as planned if the aim is to have the resting point of the rear triangle when the bike is unweighted and then when weight/bumps are applied they dont flex upwards because the curve is convex upwards as opposed to concave upwards? i am at my limit of understanding,,,,why would this not work?


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## brant (Jan 6, 2004)

dRjOn said:


> "Gotta hate those bikes. They are so lame."..at the risk of sounding like a cock...i was paraphrasing!


Perhaps pvd has different criteria for lameness ;-)



dRjOn said:


> err, but longer stays would longer no? so that would undo one of the design parameters? to have shorter wheelbase and stays...with more weight over the rear axle. if you lengthened the stays, this would mean the use of an even more relaxed seat angle and the headache that would cause in terms of front centre?


Ah - you're not understanding. I was presuming he was meaning to keep the actual bike geometry the same, but physically use longer SEAT stays - ie: attatch them in the middle of the top tube, or the head tube, or something.



> thyalcine, when you say 'in bending' etc, do you mean the seat stays are not able to work as planned if the aim is to have the resting point of the rear triangle when the bike is unweighted and then when weight/bumps are applied they dont flex upwards because the curve is convex upwards as opposed to concave upwards? i am at my limit of understanding,,,,why would this not work?


I always giggle a bit when people talk about triangles flexing. Especially one that's braced as well as the rear triangle.


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## dRjOn (Feb 18, 2004)

brant, got you, so the point under discussion is the joining point of the seat stay, in this case to the seat tube. if the seat stay joins further forward (didnt gted have a frame designed around seat tubes stretching to the head tube, and a separate assembly for the seat tube?) they have more opportunity to flex.

--- ive always wondered whether the path a structural member takes is as important as where it joins to another...i mean, for example, jones frames have an almost rhomboid rear 'triangle'...titanium is pretty ductile so being a planted layman, i would have thought the behaviour would have been somewhere between a triangle ( the points of intersection) and a rhomboid (the path of the tubes)? id love to know more about this...


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## brant (Jan 6, 2004)

Clearly, in the extreme, the path a structural member takes is important, but I think such small changes (in the grand scheme of things) don't really amount to that much. 

I think a lot of the confusion about stay bending comes from people looking at a bit of a wiggle in a tube and thinking it's going to act like a spring - a coil spring.

But a coil spring doesn't do that. A coil spring is actually a compact torsion bar - the springing action that occurs happens because the metal in the spring actually twists as it's compressed. It's not done by a column deflecting.

And remember - S bend seatstays were created in Ti, by Rob Vandermark, mostly (as I recall) to get better placement for V brake mounts (so the mounts could use less metal) and mudclearance, rather than compliance.


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## dRjOn (Feb 18, 2004)

im guessing if a seat stay was joined ahead of the seat cluster, then extra bracing would be required unless a pretty robust top tube was used? 

i would guess also that a tube would behave more like a leaf spring in this application? in terms of a leaf spring, a longer spring with similar metal properties and sizing cf a shorter would be more likely to flex given a certain force? does this apply if the length is greater but the metal is curved (ie the fulcrum and end points are the same)? in which case it may not matter whether the length is gained between axle and seat tube, or axle and join forward of the seat tube all else being roughly equal?


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## brant (Jan 6, 2004)

dRjOn said:


> im guessing if a seat stay was joined ahead of the seat cluster, then extra bracing would be required unless a pretty robust top tube was used?


Can't see that myself.



dRjOn said:


> i would guess also that a tube would behave more like a leaf spring in this application? in terms of a leaf spring, a longer spring with similar metal properties and sizing cf a shorter would be more likely to flex given a certain force? does this apply if the length is greater but the metal is curved (ie the fulcrum and end points are the same)? in which case it may not matter whether the length is gained between axle and seat tube, or axle and join forward of the seat tube all else being roughly equal?


Ah - you mean total tube length, rather than the distance between the two ends? Yes, but, no but...


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## Thylacine (Feb 29, 2004)

[email protected] said:


> Yes, but, no but...


lol

Personally I'm looking forward to the US version of Little Britain. The character of 'The only Gay in the Village' would be renamed 'The only Gay in the Village not that there's anything wrong with that I'm just sayin''

Anyways.

Carry on.


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## pvd (Jan 4, 2006)

It sounds like Brant has me covered on most points, but I should add a little more. You can increase the length of the stays by moving them forward of the seatpost (like very old GTs, not the new ones). You can also bow and bend the stay ala WTB Trailmaster or Serrotta's road design from the late nineties. The longer the stay is, the easier it is to flex especially if the geometry of the stay is giving a hand.

True, I have not ridden a Jones bike. I really don't want to, really. I've done enough testing with passive suspension and large tires to know that he is barking up the wrong tree entirely. When you get a bike like that up to speed on washboard or anything approching the natural frequency of either end, you are going to die. I've tested this. I build a fork when I was at Fat City that had 3/4" of passive travel. I thought it was great until I got going fast on some Colorado fire roads. The front wheel would actually start bouncing and skipping accross the road.

I've also tried large tires for suspension. While everyone knows that pnumatic tires are the #1 most important suspension component in any vehicle, too much of a good thing can be too much. What happens is that you go from a point of having good compliance over the surface and enough contact patch for traction and drive, to a point where the tire carcass becomes an only slightly damped spring and the squirm and drag of the tire causes poor feedback and control.

Suspension systems and quality tires are truely the way to go. On trail I use 2.1" tires and 2.35" on my downhill bike. I find that using tires any larger than this produces less control and traction and that is when I'm using well tuned, state of the art suspension.

One huge mistake I see many people making is using too light of a tire. Light tires are great if you have a race to win, but if you are looking for a quality ride that feels good with the maximum of control the carcass really does need some support. I think that more people would have much more fun by adding 100-200 grams to each end and picking up a little more speed.


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## themanmonkey (Nov 1, 2005)

When I've looked at something like the Jones design my thoughts were that more material = smoother ride. As I understand the engineering (and I could be 100% wrong) the material itself absorbs, or dissipates, energy before it gets to the rider. This isn't the same as dampening, correct? This is based mostly on empirical experiments with road frames using the same design and different weights and thicknesses of steel tubing and just a bit of reading.

I'm all for aesthetics in bike design, but cutting through the hype is just as important.


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## byknuts (Aug 9, 2008)

Thylacine said:


> It's not 'damping' what you're describing. Don't springs have a frequency, amplitude and duration, and the 'damping' is a deliberate system used to return the spring to a static state? Leaf springs as far as I understand have no damping.


you're right... and wrong... 
A single leaf spring doesn't have anything to work with for damping.
but (in theory anyways) if your leaf spring number one has say a rebound charcteristic of X and your second leaf spring has X minus 2 (due to thicker material being used for example) the second one (since they ARE held together) can slow down the whole assembly. 
Also, the bowing of the leaf spring can affect things (and sometimes they're 
This is why they run different thicknesses of the material and why there's one or two higher dollar ones that use a single leaf spring that's tapered and manipulated to emulate the multi-leaf system with less pieces. (don't know how well it works, but the theory's there)

Like I said, if someone had DECIDED that this was the ne-plus-ultra way of doing things I can see the theory they're working off of and why'd they'd insist on pursuing the methodology to achieve their goal, but it's still not a choice I'd make.
(sometimes I think there are too many designs that are created because it was decided that it's "the best way")

remember those elastomer encased springs for rock shox jett forks?! same idea, get two competing strength 'springs" one to slightly counter the other.... still, not a particularly effective system.

Anyways, this is a lot of theoretical mumbo-jumbo... engineer-ego-stroking. 
The theories are there, who bloody well knows if they're being put to use?! 
This particular design could be ENTIRELY flawed and the second set of tubes instead of acting in tandem with the first are making the whole assembly intolerably stiff and the whole "passive suspension" thing is due entirely to the big squishie tires!!

I have to remind myself to stop assuming that because there's a sound theory behind the work that means it's being properly implemented!
Shutting up now!


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## dr.welby (Jan 6, 2004)

Thylacine said:


> If you want to see what he's talking about, look at say a Silk-Ti. If you were to believe in Jeff Jones' methodology - that the seatstays are in bending - the Silk-Ti wouldn't work. The reason the Silk-Ti and other softails work is because the seatstays are predominantly in _compression,_ not bending. So knowing this engineering fact, if you wanted to make a hardtail more 'vertically compliant' (There's half the problem), you allow the seatstays to compress somehow.


I've never been able to figure out why those swoopy space frames weld the long "seatstay" pieces to the seat tube. Seems to defeat the whole purpose of them.

If anyone has one kicking around I'd be happy to do some tests on it!


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## pvd (Jan 4, 2006)

byknuts said:


> A single leaf spring doesn't have anything to work with for damping.
> but (in theory anyways) if your leaf spring number one has say a rebound charcteristic of X and your second leaf spring has X minus 2 (due to thicker material being used for example) the second one (since they ARE held together) can slow down the whole assembly.


No. Stacking springs or opposing springs changes the rate. It does not change damping.



byknuts said:


> Also, the bowing of the leaf spring can affect things (and sometimes they're This is why they run different thicknesses of the material and why there's one or two higher dollar ones that use a single leaf spring that's tapered and manipulated to emulate the multi-leaf system with less pieces. (don't know how well it works, but the theory's there)


This is friction damping from the multiple layers rubbing and hardly the design goal of this system. Friction damping is a notoriously poor form of damping.

Also, the spring rate is also at play here because a stacked system has a different moment of inertia as a solid system of the same basic shape. Depending on the application you may want stacked over solid or vis-a-vis. This is about getting the right rate and progressivity. Whatever works best is going to rule the day.


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## DWF (Jan 12, 2004)

Cantilevered tubes flex. In fact, anytime to you take a tube out of pure compression or tension, you'll see noticable flex as any one who's spent time on an alignment table will tell you. Equilateral triangles are inherently stiff (speaking with the relative terms of bicycle frames) but they're not common in bike frames. The "front triangle" is not a triangle and on many bikes, neither is the rear. Jones is big on having highly cantilevered tubes so the frame will not be as rigid as a conventional frame. I've done enough testing on conventionally attached S-bend stays to know they can indeed flex from vertical loads but we are only talking 1 or 2mm's. If you apply the same loads to a cantilevered Ti seatpost, you can get 12, even 19mms. At a slack enough angle, you're basically talking softride beam like characteristics. 

That only touches on a one perspective of hardtail/rigid frame compliance. One that most folks feel but can't define is what happens at the bottom bracket.


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## Thylacine (Feb 29, 2004)

byknuts said:


> you're right... and wrong...
> A single leaf spring doesn't have anything to work with for damping.


Well that's exactly what I said. I made no mention of friction damping between multiple leaf springs so how can I be wrong about something I didn't even say?

When I mentioned my design idea of the 'multiple leaf spring monostay', I should've mentioned they're not touching, so apologies there. Sometimes I forget the pictures in my brain others can't *ahem* see. :skep:


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## gsomtb (Jul 18, 2007)

This has to be one of the best threads I've read on mtbr yet.....
Thanks.


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## Howley (Nov 23, 2005)

*Athetics vs function*



coconinocycles said:


> since i build "cruiser" style frames, i'll chime in - yes, it is 100% cosmetic, although, the double toptube bikes are pretty stiff...........they sure look cool, though! steve.


OK looks are subjective - got it.

But I would think that a second top tube such as the one in this "Cruiser" photo has the added function of providing strength in an area I have seen photos of where frames (29er) broke some where between where this tube intersects the down tube and the head tube.

Can there be any structural gain by having a second top tube?

From what I remember of my mechanical engineering classes-a specific strength of material will sheer even with increased material. ie bolt threads- 3 threads are required any more on the nut does not matter-what matters is the composition of the material ie bolt and nut ) not he number of threads holding the 2 together.

Now you know why I flunked out of mechanical engineering at SLO...

Some thing else I picked up...The down tube is most affected by twisting forces (from the bottom bracket)- when most would assume bending forces seem logical (from the frontal impacts of the fork)

Aren't most down tube failures occurring some where between the head tube and 1/4 to 1/3 of the way toward the bb? (assuming the joint at the head tube is good)


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## Thylacine (Feb 29, 2004)

Howley said:


> Some thing else I picked up...The down tube is most affected by twisting forces (from the bottom bracket)- when most would assume bending forces seem logical (from the frontal impacts of the fork)
> 
> Aren't most down tube failures occurring some where between the head tube and 1/4 to 1/3 of the way toward the bb? (assuming the joint at the head tube is good)


There ya go, you answered your own question. How is a second top tube going to improve the torsional capabilities of the downtube? Answer - It's not.

In terms of downtube 'failures', is what you're describing the result of a frontal impact exceeding the yield of the tube?

If so, I'm not sure strengthening the downtube just for that purpose is a benefit largely because you're then transferring loads elsewhere, such as the steerer or the fork legs. Having the tubes bend and not rupture is a good thing, not a bad thing.

My face would rather have the main triangle buckle than the forks snap off.


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## Howley (Nov 23, 2005)

*TEST it!*



brant said:


> ...I might make something up with some weights and clamps and dummy axles and stuff, and throw a few frames in it to see what happens. My FEA is terrible.


Contact Mark Groendal at Energy Return Bicycles - He did this test with his SlingShot and new ERB- DYNAMOMETER back in the '80's and is using it now-http://www.erbbike.com/index-1.html

It would be neat to see a Frame Off of a say Retro Tech vs Willits - two totally opposite curves on the seat stays. Weird or What?


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## DWF (Jan 12, 2004)

Howley said:


> OK looks are subjective - got it.
> 
> But I would think that a second top tube such as the one in this "Cruiser" photo has the added function of providing strength in an area I have seen photos of where frames (29er) broke some where between where this tube intersects the down tube and the head tube.
> 
> ...


In most designs, down tubes have axial and radial stresses; most failures occur near the head tube from tensile stresses not compression. On a conventional design, the head tube is always trying to pull itself away from the downtube. Failures from frontal impacts and heavy braking loads is usually moment induced buckling.


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## dRjOn (Feb 18, 2004)

*my understanding*



dr.welby said:


> I've never been able to figure out why those swoopy space frames weld the long "seatstay" pieces to the seat tube. Seems to defeat the whole purpose of them.
> 
> If anyone has one kicking around I'd be happy to do some tests on it!


is that it is to create a spaceframe 'box' arrangement. this to affect lateral rigidity.
same as fork. using ti for forks, if you *want* to use ti, large diameters, or some tubes in push, some in pull are favourable. jeffs forks are light but very stiff in braking (no flex rearwards on braking...at all!)


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## brant (Jan 6, 2004)

dRjOn said:


> is that it is to create a spaceframe 'box' arrangement. this to affect lateral rigidity.
> same as fork. using ti for forks, if you *want* to use ti, large diameters, or some tubes in push, some in pull are favourable. jeffs forks are light but very stiff in braking (no flex rearwards on braking...at all!)


So spaceframe fork is rigid under braking, but the same arrangement in the rear triangle (join the dots), gives vertical compliance?

I will nail my beliefs to the flagpole here - I think "ride quality" comes from "splay" - ie: the wheels spreading apart under load, which is most affected by TOP TUBE section.


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## dRjOn (Feb 18, 2004)

rigid under braking as in fore aft, where the *relatively* straight tubed triangle viewed from side, would have more resistance than a similar weight total of tubing used in a more normal set up.

if that same structure was turned through 90 degrees, i would *expect* it to have some vertical compliance, like a leaf spring, but its not like for like is it?

i would suggest the triangulation is used under a different premise. in the rear- the triangle is more 'parallel' along its main members than a trad rear triangle, possibly increasing compliance, whereas the fork is a triangle compared to a single member....

thoughts?


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## pvd (Jan 4, 2006)

dRjOn said:


> Jeffs forks are light but very stiff in braking (no flex rearwards on braking...at all!)


That's called a bad fork. If a fork is not flexing under brake load then it's not flexing over bumps. If you've ridden a Yo! Eddy fork, you'd know how painful that can be. A properly designed fork has just enough flex to produce a comfortable ride, good handling, and not break or flounder in extreme situations. A properly designed frame will do the same thing in the rear. It doesn't require a space frame or goofy configurations to do this, just good tube selection for the rider and terrain and sensible quality construction.


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## DWF (Jan 12, 2004)

Most fork flex occurs in the crown and the steerer tube, not the blades themselves. The reason a properly designed truss fork works is because it shares the load between the top and bottom of the steerer tube. A fork can be rigid under braking (load towards the BB) and still flex over bumps (load away from the BB). Again, removing rider pedaling or braking forces, a down tube is under tension, not compression; the head tube is trying to pull itself away from the frame. Think about how a bike like the Slingshot works.


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## Hairllama (Oct 27, 2006)

pvd said:


> . A properly designed frame will do the same thing in the rear. It doesn't require a space frame or goofy configurations to do this, just good tube selection for the rider and terrain and sensible quality construction.


What's your view on soft tails like the YBB or Silk Ti that use no damping. Is there a point where you can have too much "forgiveness" in a rear triangle. Does a soft tail do what the Jones does with less flair?


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## brant (Jan 6, 2004)

DWF said:


> Removing rider pedaling or braking forces, a down tube is under tension, not compression; the head tube is trying to pull itself away from the frame. Think about how a bike like the Slingshot works.


That's a pretty big "remove".


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## DWF (Jan 12, 2004)

brant said:


> That's a pretty big "remove".


Not really. Tension is the primary stress, all else is secondary. By removing the confusion added by discussing pedaling influences (radial loads emanating from the ST/BB where a down tube ~never~ breaks) or braking/collision influences (moment induced buckling), it's easier to focus on the natural state of the load: tension.


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## DWF (Jan 12, 2004)

Hairllama said:


> What's your view on soft tails like the YBB or Silk Ti that use no damping. Is there a point where you can have too much "forgiveness" in a rear triangle. Does a soft tail do what the Jones does with less flair?


Depends on the direction of the "forgiveness." If it's only vertical then you have a relatively undamped (beyond the natural hysteresis of the material) spring. That would suck if you had too much of it, but it would not suck as badly as it would if all that "forgiveness" came from any other direction.


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## pvd (Jan 4, 2006)

Hairllama said:


> What's your view on soft tails like the YBB or Silk Ti that use no damping.


Those bikes have a damping system. I love softails, but I think that those two examples suck. The C'dale Scalple is about the best one ever made.


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## pvd (Jan 4, 2006)

DWF said:


> Most fork flex occurs in the crown and the steerer tube, not the blades themselves.


That's news to me.


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## Hairllama (Oct 27, 2006)

pvd said:


> Those bikes have a damping system. I love softails, but I think that those two examples suck. The C'dale Scalple is about the best one ever made.


What do you think sucks about those examples?


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## DWF (Jan 12, 2004)

pvd said:


> That's news to me.


Yeah, it's counter-intuitive.


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## pvd (Jan 4, 2006)

DWF said:


> Yeah, it's counter-intuitive.


No. It's just wrong. The blades do almost all the flexing on my forks. I can watch it happen. I know that the blades are doing a lot of work.


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## DWF (Jan 12, 2004)

pvd said:


> No. It's just wrong. The blades do almost all the flexing on my forks. I can watch it happen. I know that the blades are doing a lot of work.


Test it.


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## pvd (Jan 4, 2006)

Hairllama said:


> What do you think sucks about those examples?


Two things, the material and the spring/damper. Making a bike like this out of Ti is just silly and expensive. Aluminum and carbon are the only sensible materials and far far more cost effective. Also, both thse bikes use such lame elastomer damping or friction damping so as to be pathetic. The C'dale uses a linkage and a real shock. It's truely tunable and properly designed.


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## pvd (Jan 4, 2006)

DWF said:


> Test it.


What are you talking about? I can watch to fork blades flex! They bow under braking. They flutter over bumps. I look down the leg and see the movement. That's test enough. I'm sure that there is flex at other parts of the fork, but I know that most of the movement is coming from the blades. I've aligned thousands of forks when I was at Fat City. I know what bends on a fork. The blade. Even on the stiffest of forks. I've seen tons of destructively tested forks. I've watched them get tested. The blades flex like crazy.


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## DWF (Jan 12, 2004)

pvd said:


> What are you talking about? I can watch to fork blades flex! They bow under braking. They flutter over bumps. I look down the leg and see the movement. That's test enough. I'm sure that there is flex at other parts of the fork, but I know that most of the movement is coming from the blades. I've aligned thousands of forks when I was at Fat City. I know what bends on a fork. The blade. Even on the stiffest of forks. I've seen tons of destructively tested forks. I've watched them get tested. The blades flex like crazy.


Yes, fork blades are not infinitely rigid, they do flex, but most of that flex occurs at the crown and steerer tube. How much do you think a crown & steerer tube have to flex to allow a fork tip to "flutter" over bumps?

Think of it another way, where do you see forks fail (not including disk brake induced point loads on improperly designed forks)?


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## dr.welby (Jan 6, 2004)

DWF said:


> Test it.


Jan Heine did some fork flex tests a few issues ago in Bicycle Quarterly and, paraphrasing from memory, found that the tips were indeed providing a significant amount of flex.

I have also long been in the "fork flex comes from the crown and steerer" camp, but now I'm beginning to wonder.

This is a 10-minute FEA problem with a simplified mock-up, but I don't have access to Solidworks/Cosmos any more. Darn.


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## DWF (Jan 12, 2004)

dr.welby said:


> Jan Heine did some fork flex tests a few issues ago in Bicycle Quarterly and, paraphrasing from memory, found that the tips were indeed providing a significant amount of flex.
> 
> I have also long been in the "fork flex comes from the crown and steerer" camp, but now I'm beginning to wonder.
> 
> This is a 10-minute FEA problem with a simplified mock-up, but I don't have access to Solidworks/Cosmos any more. Darn.


Ever since VBQ admitted they couldn't take linear measurements more accurately than +/- 3mm, I've taken it all with a grain of salt.

It is easy to test though. It's also easier to understand when you consider that a steerer tube is not actually restrained by conventional headsets. If you rigidly clamp the steerer tube in place, you will obviously see no flex there and you would be confined to measuring torsional deflection at the crown and that is an order of magnitude harder to measure.

Not everything is as it seems.


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## dr.welby (Jan 6, 2004)

DWF said:


> Ever since VBQ admitted they couldn't take linear measurements more accurately than +/- 3mm, I've taken it all with a grain of salt.


Yes, though that refers to their ability measure frame dimensions. In the fork test they were measure a short distance between two objects with a set of calipers, so I assume they were able to make that measurement accurately.



DWF said:


> Not everything is as it seems.


Right, which is why the VBQ test kept me up at night. It challenged what I had previously considered to be Right, and I couldn't find a fault in their experiment. Now I'm just trying to figure out if one of the the two theories is wrong, or if both are right and there are more subtleties to fork flex than one would expect.


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## pvd (Jan 4, 2006)

It just ain't so. Sorry.


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## dRjOn (Feb 18, 2004)

dwf! interesting! thanks for the info...


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## gsomtb (Jul 18, 2007)

You guys should ask that guy w/ the bamboo and fishing line contraption from a while back what he thinks.....


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## swift (Apr 3, 2007)

It seems to me that the headset would capture the steer tube (near both extremes of its length) enough to make any flex inconsequential. Being able to quantify this flex presents the problem of differentiating steer tube flex from any bearing play present in the headset, itself.

I don't have the answers but I'd certianly like to see any reference material folks can site on this matter.


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## D.F.L. (Jan 3, 2004)

Must... stay... out... of... sh!tstorm!...Mustn't... get... dragged... in!

Oh, hell.

there is some flex between the headset bearings. Not a huge amount on 1 1/8 and reasonable travel forks, but go to 1", especially in carbon, and those things can flex quite a bit.

Everything flexes; let's not fight. Why not get back to hatin' on Jones?


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## Thylacine (Feb 29, 2004)

It's strange though. We had a road bike of ours tested (Columbus XCR, 1 1/8th Chris King aheadset, Edge composites fork, 38mm downtube) and another bike in the shootout was the Colnago Master-Light (oxymoron)(Columbus whatever, 1" ahead Campy, Steel fork, 31mm downtube) and the deflection at the headtube was the same on both bikes, right down to two decimal places.

I think there's stuff going on in the headset that we don't fully understand (or carbon forks are much flexier than we realise). Or at least I don't, because everything here points to our bike being massively stiff and it just wasn't in comparison.


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## shiggy (Dec 19, 1998)

DWF said:


> Yes, fork blades are not infinitely rigid, they do flex, but most of that flex occurs at the crown and steerer tube. How much do you think a crown & steerer tube have to flex to allow a fork tip to "flutter" over bumps?
> 
> Think of it another way, where do you see forks fail (not including disk brake induced point loads on improperly designed forks)?


I Know! I Know!. I built a fork last year and it failed--and in the same place my mtb forks failed in the '80s. The steer tube bent forward from vertical loads. Not backward from braking or frontal impact.

There is a reason mtb forks have evolved with larger diameter steerers and/or double crowns.


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## shiggy (Dec 19, 1998)

Thylacine said:


> It's strange though. We had a road bike of ours tested (Columbus XCR, 1 1/8th Chris King aheadset, Edge composites fork, 38mm downtube) and another bike in the shootout was the Colnago Master-Light (oxymoron)(Columbus whatever, 1" ahead Campy, Steel fork, 31mm downtube) and the deflection at the headtube was the same on both bikes, right down to two decimal places.
> 
> I think there's stuff going on in the headset that we don't fully understand (or carbon forks are much flexier than we realise). Or at least I don't, because everything here points to our bike being massively stiff and it just wasn't in comparison.


I do not understand what the "deflection at the head tube" means or how the fork would/should affect it.


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## Thylacine (Feb 29, 2004)

Well, they bolt down the frame/forks at the dropouts, stick 40kg on one 'crankarm' and measure at various points on the frame how far out of plane the thing is.

Yes yes I know it's flawed methodology, but it's not my test.


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## shiggy (Dec 19, 1998)

Thylacine said:


> Well, they bolt down the frame/forks at the dropouts, stick 40kg on one 'crankarm' and measure at various points on the frame how far out of plane the thing is.
> 
> Yes yes I know it's flawed methodology, but it's not my test.


Are they measuring lateral deflection of the head tube? Seems the fork blades/steer tube would make little difference unless they were REALLY wimpy. Says nothing about how the fork reacts under non-pedaling riding conditions, either.


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## shiggy (Dec 19, 1998)

brant said:


> So spaceframe fork is rigid under braking, but the same arrangement in the rear triangle (join the dots), gives vertical compliance?
> 
> I will nail my beliefs to the flagpole here - I think "ride quality" comes from "splay" - ie: the wheels spreading apart under load, which is most affected by TOP TUBE section.


"Splay" is what a Slingshot frame is all about. It is a different ride feel than any rigid or suspension frame I have ever ridden. I also like the ride. I like the ride Brant puts into his frames, too.

hmmmm...I just had a idea for a frame that will probably make many of you cringe...


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## dr.welby (Jan 6, 2004)

OK, fair warning here, I learned the basics to this FEA program (LISA) in 15 minutes and my FEA experience is confined to college 15 years ago, so take this with a healthy dash of salt. I did this because, as I mentioned upthread, Jan Heine's fork deflection tests in Vintage Bicycle Quarterly Vol. 6, Number 3 were keeping me up at night and now this thread is contributing to my insomnia.

So here's some really raw, basic FEA on a straight and curved fork.

*What's going on:* Both have the same dimensions top and bottom as well as rake. They have approximately fork-like dimensions. I have modeled them as simple planar meshes in 2D. The top of the blade is constrained, a vertical load is applied at the tip of the blade. The same loads, constraints, and material properties were used on both simulations.

*What's not going on:* I am not modeling flex in steerer tubes, crowns, etc. I am only looking at vertical loading, not brakes loads or anything more complicated. I am not bringing a wealth of experience or knowledge to this exercise.

*So that said* - here's the interesting part - the curved fork deflected vertically .88 units. The straight fork deflected .59 units. Generally I would assume that the top of the blades and the unmodeled crown and steerer would deflect the same on either design, so the extra flex must be coming from bend in the lower portion. So I don't think it's as simple as saying "fork flex comes from the crown". Or maybe I'm screwing up. It's possible.

I need to play with this some more so if anyone has any insights I'll try to add them to my further tests.


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## brontotx (Apr 5, 2006)

shiggy said:


> I do not understand what the "deflection at the head tube" means or how the fork would/should affect it.


Most of the braking load will be exerted at the longest moment, which is the head tube. My experience/observation with my black sheep ti truss fork is that there is a small deflection of the whole fork at the head tube AND more along the blades.


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## themanmonkey (Nov 1, 2005)

Thylacine said:


> I think there's stuff going on in the headset that we don't fully understand (or carbon forks are much flexier than we realise). Or at least I don't, because everything here points to our bike being massively stiff and it just wasn't in comparison.


An interesting thing I discovered a few years back. I was working at a high-end road shop in Vancouver, B.C. and had a maybe a dozen guys come in 2 years with really strange wear spots on the front of their carbon steerers. It was pretty obvious that the steerers were flexing and rubbing against the upper headset cup.

The first few we just showed to the customers and replaced the fork. I talked to a bunch of different fork and bike makers and no one could explain it. I started asking the folks with the problem forks about their riding habits and such. Each and everyone was a big descender and loved screaming down places like Mt. Seymour (The north shore's not just for MTB riding.) and they all controlled their speed with the front brake.

So my conclusion was the hard braking through corners was flexing the steerer enough so that it was touching the headset cup. In theory the headset should have gotten tighter, but none of the riders asked noticed that during their descent. This is where I think your first sentience in the quote is dead on.

Those of us that have been cyclists for a long time have seen a ton of anecdotal stories that break from the scientific beliefs or predictions of engineers. Similar to *DWF*'s statement about the flex being most in the steerer and crown. I know the test he's talking about and will see if I can find it in my archives.


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## shiggy (Dec 19, 1998)

brontotx said:


> Most of the braking load will be exerted at the longest moment, which is the head tube. My experience/observation with my black sheep ti truss fork is that there is a small deflection of the whole fork at the head tube AND more along the blades.


I was asking about the testing Thylacine referred to, not how it works when ridden.


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## Hairllama (Oct 27, 2006)

pvd said:



> Two things, the material and the spring/damper. Making a bike like this out of Ti is just silly and expensive. Aluminum and carbon are the only sensible materials and far far more cost effective. Also, both thse bikes use such lame elastomer damping or friction damping so as to be pathetic. The C'dale uses a linkage and a real shock. It's truely tunable and properly designed.


You mentioned that Ti is a bad material for a soft tail? Why do you think this is the case? What is your view of titanium as a frame material overall? The discussion or fork stresses is fascinating. I'm really curious about the view on rear triangle forces especially in regard to soft tails or curvy stays.


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## shiggy (Dec 19, 1998)

themanmonkey said:


> An interesting thing I discovered a few years back. I was working at a high-end road shop in Vancouver, B.C. and had a maybe a dozen guys come in 2 years with really strange wear spots on the front of their carbon steerers. It was pretty obvious that the steerers were flexing and rubbing against the upper headset cup.
> 
> The first few we just showed to the customers and replaced the fork. I talked to a bunch of different fork and bike makers and no one could explain it. I started asking the folks with the problem forks about their riding habits and such. Each and everyone was a big descender and loved screaming down places like Mt. Seymour (The north shore's not just for MTB riding.) and they all controlled their speed with the front brake.
> 
> ...


I experienced the same type of rub marks on one of my mtbs. The aluminum steer tube had a heavy mark on it at the level of the lower cup. Had Marzocchi replace it with a steel steerer and there has been no new contact marks.

And yes, I am a heavy front brake user (not a heavy rider).


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## themanmonkey (Nov 1, 2005)

shiggy said:


> I experienced the same type of rub marks on one of my mtbs. The aluminum steer tube had a heavy mark on it at the level of the lower cup. Had Marzocchi replace it with a steel steerer and there has been no new contact marks.
> 
> And yes, I am a heavy front brake user (not a heavy rider).


I had seen it a few times over the years on aluminum steerers, but never ti or steel. The aluminum steerers I checked were mostly bent slightly, though all the carbon ones were straight when I checked. Did you check to see if the steerer actually bent?

*Shiggy* you might actually be able to test this if they still have the old frame testing machine from way back in the BF storage warehouse. If I remember it was designed to test the stem and fork flex, so it shouldn't be hard to adapt to a "normal" fork.


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## teamdicky (Jan 12, 2004)

themanmonkey said:


> An interesting thing I discovered a few years back. I was working at a high-end road shop in Vancouver, B.C. and had a maybe a dozen guys come in 2 years with really strange wear spots on the front of their carbon steerers. It was pretty obvious that the steerers were flexing and rubbing against the upper headset cup.


Just curious...

Were they using King HS?

http://www.pvdwiki.com/index.php?title=The_BEST_Headset

Like I said, just curious.


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## swift (Apr 3, 2007)

D.F.L. said:


> Everything flexes; let's not fight. Why not get back to hatin' on Jones?


I'm not hatin' on anyone. ...But that is funny.


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## themanmonkey (Nov 1, 2005)

teamdicky said:


> Just curious...
> Were they using King HS?


At least one was, but there were some Campy, Shimano, and integrated in there too. It was also a variety of forks too, many of them "stock" forks. The steerer length didn't seem to matter too much on the carbon forks, but the couple aluminum ones were all longish.

EDIT: Just read Peter's wiki and that's just what we call "Chris King syndrome" and what I was seeing was different and lower on the steerer. He's also 100% correct on the write up including the love for S-3.


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## teamdicky (Jan 12, 2004)

themanmonkey said:


> At least one was, but there were some Campy, Shimano, and integrated in there too. It was also a variety of forks too, many of them "stock" forks. The steerer length didn't seem to matter too much on the carbon forks, but the couple aluminum ones were all longish.
> 
> EDIT: Just read Peter's wiki and that's just what we call "Chris King syndrome" and what I was seeing was different and lower on the steerer. He's also 100% correct on the write up including the love for S-3.


Thanks for clarifying.


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## Thylacine (Feb 29, 2004)

All I have to say is....


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## pvd (Jan 4, 2006)

Hairllama said:


> You mentioned that Ti is a bad material for a soft tail? Why do you think this is the case? What is your view of titanium as a frame material overall? The discussion or fork stresses is fascinating. I'm really curious about the view on rear triangle forces especially in regard to soft tails or curvy stays.


The reason why Ti is not a very good material for Softails is exactly the same as why Ti and Steel are poor choices for suspension bikes in general. The added cost of the material and the flexibility that is otherwise a benefit on a hardtail is a detrement when adding mechanical controlled flex to the rear. Also, integrating bosses and supports to the chassis to hang the system parts add lots of weight and cost to what could be done with aluminum in a very light and cheap way. By engineering a carbon spar to flex, the entire rest of the chassis can be made very stiff, strong, light, and cheap. The new Scalpel with the improved linkage is an incredible bike. I've ridden it. It's one of the best honest trail bikes I've ever been on (I would just like my geometry and choice of front ends on it). Take one for a test ride and you will see what I'm talking about.

Another problem with most "high end" softtail designs is that they use very very crude spring/damper systems. Essentially relying on friction damping at best. The "shocks" are also used as stressed members, a horrible mistake that ruins any good that could result from the simple system. They are prone to contaiminaiton and produce a lot of friction. The older Trek and the current Scalples use actual shocks that are used only to absorb and control motion and not to support the bike structure. This increases the life of the shock, reduces friction and heat, and makes it possible to truely tune the system.

I think that Ti is a wonderful material for hardtail mtb's if you can handle the cost for what could be a slight increase in feel. If I didn't make my own steel bikes, I would only be interested in riding Carbon road bikes. Anything with a rear shock just has to be made from Aluminum.


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## morandi (Jun 20, 2008)

pvd said:


> That's called a bad fork. If a fork is not flexing under brake load then it's not flexing over bumps. If you've ridden a Yo! Eddy fork, you'd know how painful that can be. A properly designed fork has just enough flex to produce a comfortable ride, good handling, and not break or flounder in extreme situations. A properly designed frame will do the same thing in the rear. It doesn't require a space frame or goofy configurations to do this, just good tube selection for the rider and terrain and sensible quality construction.


 The Jones Spaceframe design is mainly about looks. The biggest difference between the spaceframe and the diamond frame is standover clearance. Riding a Jones diamond frame head to head with a spaceframe I could detect no difference in ride quality and comfort. Sorry.
On a rigid bike to me I notice the biggest difference in your contact points. Like wheel and tire choice, seatpost material and extension, handlebar material, grip choice, saddle choice and rider position on the bike. 
I like riding rigid bikes, and Jones rigid bikes to me work better than others. But not because of crazy tube configurations but because of how they positon me on the bike.
The fork design to me does work. Its light, strong, and tracks really well. I know exactly how its going to react in the majority of situations, and most importantly it does not change the geometry of the bike everytime I go over a bump.


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## shiggy (Dec 19, 1998)

themanmonkey said:


> I had seen it a few times over the years on aluminum steerers, but never ti or steel. The aluminum steerers I checked were mostly bent slightly, though all the carbon ones were straight when I checked. Did you check to see if the steerer actually bent?
> 
> *Shiggy* you might actually be able to test this if they still have the old frame testing machine from way back in the BF storage warehouse. If I remember it was designed to test the stem and fork flex, so it shouldn't be hard to adapt to a "normal" fork.


I do not remember if the AL steerer was bent or not. I did check it and had it replaced because I did not trust it.

I will look for the testing rig.


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## Hairllama (Oct 27, 2006)

pvd said:


> The reason why Ti is not a very good material for Softails is exactly the same as why Ti and Steel are poor choices for suspension bikes in general. The added cost of the material and the flexibility that is otherwise a benefit on a hardtail is a detrement when adding mechanical controlled flex to the rear.


I agree that aluminum is best for a true full suspension design. When compliance is controlled by shocks the natural flex of titanium is a hinderance since the system need to remain stiff to get full benefit from the shocks. I had assumed that titanium was a decent material for a softail since the natural flex of the material could be used to its greatest advantage.



pvd said:


> Another problem with most "high end" softtail designs is that they use very very crude spring/damper systems. Essentially relying on friction damping at best.


The Moots design is crude, I think I saw something similar posted on a frame from the turn of the century. For me that's part of the appeal. It very low tech and doesn't need a pump or pivots to make it work. Call it luddite suspension. I just wonder if there's ever a situation where the frequency of bumps in the road could get the rear to cycle in such a way that it could cause the rider to loose control. I'm guessing that that situation exists in theory, but not in practice.


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## Pooh Bear (May 25, 2006)

D.F.L. said:


> Oh, hell.
> 
> there is some flex between the headset bearings. Not a huge amount on 1 1/8 and reasonable travel forks, but go to 1", especially in carbon, and those things can flex quite a bit.


Well, as a rider of rigid bikes exclusively I'd like to comment on that one.
My main ride is a 1994 Tange Ultimate Superlight steel frame with a headtube for 1" steerers. When I built this "retro frame" up in 2005 my other bike was an up to date Reynolds 853 frame with a common 1 1/8" steerer. 
Now I noticed very different ride characteristics in the front end between both frames. The 1" one would definetely have more "give". While (at least subjectively) being just as stiff while pedaling. They were actually build up with nearly the same forks (el cheapo Tange MTB forks which differed only in steerer diameter (and colour)). 
Because of that I think there's a lot to the theory of the steerer being one of the most responsible parts for fork flexing. Still I can see the fork blades flexing while riding - of course seeing the whole frame expecially the headtube flexing while riding it would be a bit disconcerting.

Another thing: Death defying as I am I rode said retro frame with a Chinese Ti fork (580gr.) for about 2 years. There were a lot of news concerning those forks breaking at the fork blades. My fork didn't break even under heavy breaking combined with some, er, rider errors. 
Now the thought: It simply didn't break because the loads were distributed better over the whole fork. Maybe the 1" steerer took the load better than a 11/8" steerer would have done. The latter one being the stiffer steerer may have led to a fork blade failure.

What do you think about this?


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## rocwandrer (Oct 19, 2008)

pvd said:


> The reason why Ti is not a very good material for Softails is exactly the same as why Ti and Steel are poor choices for suspension bikes in general. The added cost of the material and the flexibility that is otherwise a benefit on a hardtail is a detrement when adding mechanical controlled flex to the rear. Also, integrating bosses and supports to the chassis to hang the system parts add lots of weight and cost to what could be done with aluminum in a very light and cheap way. By engineering a carbon spar to flex, the entire rest of the chassis can be made very stiff, strong, light, and cheap. The new Scalpel with the improved linkage is an incredible bike. I've ridden it. It's one of the best honest trail bikes I've ever been on (I would just like my geometry and choice of front ends on it). Take one for a test ride and you will see what I'm talking about.
> 
> Another problem with most "high end" softtail designs is that they use very very crude spring/damper systems. Essentially relying on friction damping at best. The "shocks" are also used as stressed members, a horrible mistake that ruins any good that could result from the simple system. They are prone to contaiminaiton and produce a lot of friction. The older Trek and the current Scalples use actual shocks that are used only to absorb and control motion and not to support the bike structure. This increases the life of the shock, reduces friction and heat, and makes it possible to truely tune the system.
> 
> I think that Ti is a wonderful material for hardtail mtb's if you can handle the cost for what could be a slight increase in feel. If I didn't make my own steel bikes, I would only be interested in riding Carbon road bikes. Anything with a rear shock just has to be made from Aluminum.


Aluminum is a pretty bad choice for a frame that relies on chainstay flex instead of a pivot. Steel, Ti, and carbon are good choices. Why do i feel that way? Fatigue life.

I do agree that those horrible elastomers should never be used on any bike for suspension. ignoring everything else about them, the damping rate changes as a strong function of temperature, and the spring rate changes as a function of age and use.


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## pvd (Jan 4, 2006)

rocwandrer said:


> Aluminum is a pretty bad choice for a frame that relies on chainstay flex instead of a pivot. Steel, Ti, and carbon are good choices. Why do i feel that way? Fatigue life.


Of couse it is a poor choice for the flexing member. That is why I side with Cannondales use of carbon fibre for the flex. It can be engineered to meet the conditions perfectly and has it's own springing properties. Nobody on this board is silly enough to suggest using aluminum to flex a softtail, but it is perfect for the rest of the chassis.



pvd said:


> By engineering a carbon spar to flex, the entire rest of the chassis can be made very stiff, strong, light, and cheap. The new Scalpel with the improved linkage is an incredible bike.


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## SuspectDevice (Apr 12, 2004)

rocwandrer said:


> Aluminum is a pretty bad choice for a frame that relies on chainstay flex instead of a pivot. Steel, Ti, and carbon are good choices. Why do i feel that way? Fatigue life.
> 
> QUOTE]
> 
> ...


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## rocwandrer (Oct 19, 2008)

SuspectDevice said:


> rocwandrer said:
> 
> 
> > Aluminum is a pretty bad choice for a frame that relies on chainstay flex instead of a pivot. Steel, Ti, and carbon are good choices. Why do i feel that way? Fatigue life.
> ...


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## SuspectDevice (Apr 12, 2004)

rocwandrer said:


> [
> 
> weren't those rear ends as twisty as wet noodles though?


And if they were, wouldn't that make your earlier argument about flex in Alumium yadda, yadda be ever more specious?


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## itsdoable (Jan 6, 2004)

Thylacine said:


> All I have to say is....


Is that the same as:








(https://forums.mtbr.com/showthread.php?t=482263)
I remember hearing several similar reported issues, but maybe that was just with the 1st batch?

Any decent cup & cone threadless headset with a split compression ring on the top race is fine with me. One of you should be able to modify and sell a split compression ring unit to replace the CK O-ring top cap mess.


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## Thylacine (Feb 29, 2004)

If you google any product, you'll see failures of it on mtbr, so I'm not taking it as a systemic failure based on a whole two instances.

We've been using the Crank Bros headsets in XC applications and so far no issues, so we'll see how it goes. Fingers crossed because they have a lot of potential.


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## teamdicky (Jan 12, 2004)

itsdoable said:


> One of you should be able to modify and sell a split compression ring unit to replace the CK O-ring top cap mess.


From Vertigo Cycles:


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## pvd (Jan 4, 2006)

As most of you know, I'm a big fan of integrated head systems. Since I have first used it I have been able to feel the difference on back to back tests. They not only look better and reduce parts, they honestly make the bike work better.

I've been designing and testing a system for frambuilders that is cleaner and easier than other offerings for using this system. At one point, to test a procedure, I pressed in some modular units without brazing them in place. This was a serious press fit done in a hydraulic press. Steel against steel without lube, enough to expand the outer tube slightly. 2 mtb's and one road bike. The technique worked just fine on the road bike, to this day (about 3k miles). The mountain bikes didn't fair to well. The setup on the rigid front end saw the paint begin cracking almost immediately, quickly working all the way around. The setup on the front suspension bike worked at first but began cracking the paint once the bike was very aggressively ridden. Stripping the paint and fillet brazing in place has cured the problem. I'm getting a bunch of parts CNC'd this week. 8 months of testing and several redesigns!

WHAT I LEARNED: Even with this industrial press fit, steel on steel, the cups would shift in the head tube. If had not painted over the joint, I would not have seen this and would have doubted it. On a traditional pressed in headset, the fit is not as tight and is usually aluminum in steel, sometimes with hardly any interference and a much larger moment. I am sure that a huge amount of movement is taking place on this system (although not producing the movement that DWF mentions). Basically, the traditional system is complete and utter garbage. I'm never going back.

Take a look at some parts that I may have up for sale in the next week or so.

Here is a photo of some cracked paint:


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## crux (Jan 10, 2004)

This thread has been quite interesting to follow.

While I would agree with PVD to a point on integrated headsets. There is some consern on ovalizing the head tube, or someone using the old 2x4 method of install and killing the frame vs a replaceable component. If someone is using the 2x4 method then that is their own fault. Know I'll catch some flack for this statement, but it is just one view point.

Also back to the dual top tube design bikes sure they have a bit of a different style compared to the modern traditional diamond frames, but calling them fashion bikes? Not to sure about that. Some observations from riding a BS Highroller, it seems to ride as anyother bike. When standing and really torquing the frame there is some side to side flex. On decents if your really leaning into it there is some minimal flex as well. The real PITA is when or if you ever need to carry the bike over your shoulder as the center tube is just in the way. Have thought quite a bit about bike packing and think that a center tube opens up a few options not avaliable on a standard frame in packing supplies to the frame, but that is an experiment for this summers trip. 

What about the Retrotec Twin / Tripple, or Pereira Roaring?


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## rocwandrer (Oct 19, 2008)

SuspectDevice said:


> And if they were, wouldn't that make your earlier argument about flex in Alumium yadda, yadda be ever more specious?


absolutely not, but I can see why you would say that.


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