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  1. #1
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    Titanium pivotless frames?

    Any thoughts please from a builders point of view on a titanium pivotless frame with a flex plate.

  2. #2
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    Quote Originally Posted by cabbgage View Post
    Any thoughts please from a builders point of view on a titanium pivotless frame with a flex plate.
    Castellano would probably build one for you. They've got the aluminum one. Castellano Designs | Fango at a Glance Ibis marketed a titanium version of the bike years ago. There were a couple of other softail designs

    The popularity of the design has waned. People like their bikes to look like motorcycles.

    Still a good idea IMHO.
    Last edited by asphalt_jesus; 04-03-2012 at 04:32 PM.

  3. #3
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    Quote Originally Posted by cabbgage View Post
    Any thoughts please from a builders point of view on a titanium pivotless frame with a flex plate.
    I don't build bikes, but have rode them. Look at Van Nicholas bikes, they
    look functional and pretty to me.
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    Black Sheep has made a bunch of them. I saw one at the Richmond NAHBS a couple years ago. It doesn't have to be titanium, either. Salsa has a couple of aluminum frames with the flexy chainstays, and if you wanted a custom built frame, there's the Scotchflex composite out there. I have a big chunk of flexible carbon fiber that I'm going to use in a fs frame...real soon now. Really.

    There's nothing wrong with the idea, but take a close look at any particular builder's version, and make sure they'll stand behind it.

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    I rode a Morati softail for a few races years ago.
    The dust line on the seatstay shock said that it really did work but I was so focused on the horrible chain suck that the bike was prone to that I just didn't care about it's effectiveness.
    I couldn't be done with that bike fast enough.

  7. #7
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    Im looking at la ruta, im confident that the bike is good, my concerns are durability, flex, and things like chain suck and bobbing that i dont really understand.
    So much money is spent on modern suspension designs, can a simple pivotless one be as good?
    Im drawn towards it for its simlicity and weight savings.

  8. #8
    craigsj
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    I'd say "frame builder" isn't the same as "suspension designer".

    A flex plate is an alternative to a pivot, not an alternative to a suspension design. I'm also interested in builders' opinions on how well they work, but all the soft-tails I've seen have flex plates immediately behind the bottom bracket which is a terrible location. I've long wondered why builders of these designs haven't moved beyond that like everyone else.

  9. #9
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    Why is it a terrible location for the flex plate?

  10. #10
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    Quote Originally Posted by cabbgage View Post
    Why is it a terrible location for the flex plate?
    It is a terrible location for the main pivot whether it is a flex plate or not.

    A pivot location directly behind the bottom bracket produces a suspension with substantial pedal bob. Furthermore, pedal bob gets worse as you move deeper into travel. Such designs have little variance in chain growth which people view as a feature but it comes at a high cost. The axle path in such designs is always moving forward which is bad for compliance.

    Softtails typically have low travel so pedal bob isn't so easily noticed. Poor small bump compliance will tend to cover up pedal bob as well, so things like shock rate and shock platform can affect perception of pedal bob. The rider should want good small bump compliance, though.

    There is no reason for a flex plate design to have this limitation but I've never seen one that didn't. I've recently discussed this with a custom builder but am not sure what will come of it.
    Last edited by craigsj; 03-11-2014 at 06:08 PM.

  11. #11
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    Funk cycles say that there is little or no pedal bob. Do you think that is not true? I live in Spain and there is no way to try the bike first (it will be raced - so bobbing is not something i want)

  12. #12
    craigsj
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    Quote Originally Posted by cabbgage View Post
    Funk cycles say that there is little or no pedal bob. Do you think that is not true? I live in Spain and there is no way to try the bike first (it will be raced - so bobbing is not something i want)
    The suspension design has a lot of pedal bob inherent in it. The effect can be masked by shock platform and a stiff spring rate so I can't say how noticable it is having not ridden one. What I can say is that people will say all sorts of things that may have little to do with reality, and that a design like the La Ruta will either have pedal bob, low compliance, or a lot of propedal...probably a combination of those things.

    I suspect racers tend to like firm, low travel, low compliance suspensions so it would not surprise me to hear that some like the La Ruta. The La Ruta design, though, is limited to low travel and compliance and is as primitive as it gets. No reason that flex plates have to be that way. If this is really a question on how the La Ruta rides I'm not qualified to say.

    Softtails aren't the only bikes with this kind of pivot design. Lenz makes the MilkMoney with "concentrak" which is largely the same. Unsurprisingly, some say how great it is while others complain about the pedal bob.

    Over in the custom builder's forum there was a poster recently that complained that he wasn't getting sufficient travel out of his softtail Black Sheep. It appeared Black Sheep provided a shock that was too stiff and his complaints were solved by working with Push. He didn't say how pedal bob was effected or anything other than how much happier he was with the increased compliance. I mention this because there's a lot more to a bike than just how its pivots are implemented.
    Last edited by craigsj; 04-04-2012 at 07:53 AM.

  13. #13
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    Can you recomend anywhere on the internet where i can read up about suspension, this is all very interesting, but i don't really know very much about the subject.

  14. #14
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    I recommend Tony Foale's book Motorcycle Handling and Design. The basic design principles for motorcycles and bicycles is the same. You can also play with the Linkage design software and read Antonio Osuna's blog.

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    As said earlier there is no getting away from the point a pivot is still a pivot doesn't matter if it is a flexure or a bearing of some sort ,

    I used to work in f1,when we went from spherical bearings to flexures on the wishbones there was less friction in the system but we initially had problems oof the flexures being over flexed during building the car, the joints were accidentally moved through more movement than their elastic limit ,

    On a car the two joints were a big distance apart so were very stiff in torsion maybe the current designs rely on the seat stays and shock to maintain torional stiffness ,

    I think with some clever design they have a lot to offer , an estay design comes to mind to get the pivot in the right area as normal single pivot designs

  16. #16
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    Quote Originally Posted by ade ward View Post
    I think with some clever design they have a lot to offer , an estay design comes to mind to get the pivot in the right area as normal single pivot designs
    Exactly!

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    Quote Originally Posted by craigsj View Post
    The rider should want good small bump compliance, though.
    A rider that prefers soft tail designs DOESN'T WANT SMALL BUMP COMPLIANCE. The entirety of your argument is based on insistence that small bump and big-bump compliance performance should be near equal. Eliminate small bump compliance from your argument and there's not much left.

    It's a viable method of providing some suspension at very low weights and mechanical simplicity. Very low weight and big-hit compliance are legitimate needs for the XC racing community.

  18. #18
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    As ive said i really dont know much about all this, but i do race xc, at the mo i have a hard tail, my idea for going full sus is to help smooth out the rides on stoney, small rock terrain, which after 2hrs take their toll on you. I think you call this small bump compliance.Weight for me is very important, but inefficency is worse.

  19. #19
    craigsj
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    Quote Originally Posted by asphalt_jesus View Post
    It's a viable method of providing some suspension at very low weights and mechanical simplicity. Very low weight and big-hit compliance are legitimate needs for the XC racing community.
    I agree, but...

    Quote Originally Posted by asphalt_jesus View Post
    A rider that prefers soft tail designs DOESN'T WANT SMALL BUMP COMPLIANCE.
    I don't agree. A rider that prefers soft tail designs accepts poor small bump compliance because that's how they are. They could be better if designed differently and the difference in design would not make them heavier or more complex. That gets far off the OP's question, though.

    Nobody ever said they wanted simple, lightweight, short travel suspension but with BAD small bump compliance. Ever.

    Quote Originally Posted by asphalt_jesus View Post
    The entirety of your argument is based on insistence that small bump and big-bump compliance performance should be near equal. Eliminate small bump compliance from your argument and there's not much left.
    I don't know where you are getting this. I said that riders should want small bump compliance...and they should. Riders can do without it, of course, and they can do without big hit capability too. Those are called hard tails and they pedal well. The key thing is that soft tails could do better except that builders of those designs haven't advanced the art. Small bump compliance is good for comfort and for traction/control. No one was ever served well doing without it.

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    Quote Originally Posted by craigsj View Post
    They could be better if designed differently and the difference in design would not make them heavier or more complex.
    To make your point work you are pretending that a linkage-less suspension system that gives a rider every suspension feature they could ever want is ready and waiting. As if someone just needs a little time and money to get it to market.

  21. #21
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    Quote Originally Posted by asphalt_jesus View Post
    To make your point work you are pretending that a linkage-less suspension system that gives a rider every suspension feature they could ever want is ready and waiting. As if someone just needs a little time and money to get it to market.
    Nice straw man. There's a difference between "better than what exists now" and "every suspension feature they could ever want". You are now arguing out of anger.

    Not sure what you mean by "linkage-less". There are softtails with shock linkages.

    Take a typical softtail, the La Ruta for instance, elevate the flex plate to the height of the middle ring and perhaps move it forward to the downtube. There's your improved design. See, that wasn't too hard. There are countless examples of this exact design except that they have a pivot rather than a flex plate. The entire full suspension world knows roughly where the pivot should go except for softtail builders.

    This is not a difficult concept for people who understand basic suspension design, but frame builder does not mean suspension designer.
    Last edited by craigsj; 03-11-2014 at 06:12 PM.

  22. #22
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    As we know life is not simple, you can't have it all
    But a soft tail design should be able to give you good pedaling with the correct pivot position, just take a look at current single pivot bikes for the position ,

    Simple single pivot designs normally have a falling rate spring rate
    So a linkage may be of help to control the change in spring rate, this also might help if correctly designed to increase the torsional stiffness of the rear end and lessen any side loading to the shock

    If this was my bike I would be happy to sacrifice a little small bump sensitivity to help smooth out the bigger hits as we have limited travel

  23. #23
    craigsj
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    Quote Originally Posted by ade ward View Post
    Simple single pivot designs normally have a falling rate spring rate So a linkage may be of help to control the change in spring rate, this also might help if correctly designed to increase the torsional stiffness of the rear end and lessen any side loading to the shock
    I attached a picture of a recently posted Black Sheep that implements what you are describing. I agree.
    Quote Originally Posted by ade ward View Post
    If this was my bike I would be happy to sacrifice a little small bump sensitivity to help smooth out the bigger hits as we have limited travel
    That is the compromise that people make, but the limited travel itself is driven by a number of issues including lack of shock linkage and poor control of pedal bob. I don't see why a design that includes flex plates should be limited to short travel nor do I consider flex plate synonymous with soft tail.
    Attached Thumbnails Attached Thumbnails Titanium pivotless frames?-2012-03-29_16-59-47_718.jpg  


  24. #24
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    Cannondale Scalpel. It's not titanium, but it's pivotless and available. No idea how they ride, of course.

    Personally if I were to have some aspect of my suspension magically improved, it would be small bump compliance. I have to soak up big hits with my arms and legs regardless. Being able to pedal and track more smoothly on more chattery trails would be pretty cool.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  25. #25
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    Quote Originally Posted by craigsj View Post
    Nice straw man. There's a difference between "better than what exists now" and "every suspension feature they could ever want". You are now arguing out of anger.

    Not sure what you mean by "linkage-less". There are softtails with shock linkages.

    Take an typical softtail, the La Ruta for instance, elevate the flex plate to the height of the middle ring and perhaps move it forward to the downtube. There's your improved design. See, that wasn't too hard. There are countless examples of this exact design except that they have a pivot rather than a flex plate. The entire full suspension world knows roughly where the pivot should go except for softtail builders.

    This is not a difficult concept for people who understand basic suspension design, but frame builder does not mean suspension designer.
    Two questions if you wouldn't mind:

    1. Do you know if any softtails exist as you describe?

    2. In your opinion, without going too OT, what is the best suspension design for XC racing?

  26. #26
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    Quote Originally Posted by jtmartino View Post
    Two questions if you wouldn't mind:

    1. Do you know if any softtails exist as you describe?

    2. In your opinion, without going too OT, what is the best suspension design for XC racing?
    I do mind being trolled. This thread is not about me.

    Your second question is entirely OT. If you know of an example in your first question, I'm sure the OP would be interested.

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    Hi guys, This is quite an awesome thread with heaps of information that backs up just what I have been thinking for a while. Therefore I perceive craigsj as correct ,

    I am planning on building a bike in just this sort of design from Ti as another of my weird prototypes, material ordered

    The only thing that I am not sure about is the flex plate, to maintain a reasonable life you would need to be within certain boundaries, ie, length of plate, thickness, grade of Ti and angle of bend. No-one is probably willing to surrender this info, but you don't know unless you ask .........crickets.........

  28. #28
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    ^^^
    What's your background in this stuff?

    You can actually find a lot of information about materials properties for free or for relatively reasonable amounts of money online. It's not like you're the first person to wonder how much cyclical loading a titanium spring can withstand.

    matweb.com is a good place to start. They mostly have information provided by manufacturers, and it's free.

    These guys are authoritative, but everything costs money.
    ASM International Homepage | The Materials Information Society

    If you're near a university with an engineering school, ASM's handbooks, or something similar, are probably in their engineering library.

    If I was designing a part to flex, I'd figure out the boundaries of its flexion, back-calculate peak stresses from that, give it a nice, big safety factor, like 3, and then use as much material as it took to keep that at or below the material's endurance limit. (Not sure if titanium has an endurance limit. But if it does...)
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  29. #29
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    Oh, another place to look - patents. If someone has made this system work, or at least thought they did, they probably patented it. It would be a very egotistical designer who didn't take a look at the state of the art before getting started.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  30. #30
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    Quote Originally Posted by craigsj View Post
    I do mind being trolled. This thread is not about me.

    Your second question is entirely OT. If you know of an example in your first question, I'm sure the OP would be interested.
    Calm down man, I wasn't trolling. You clearly are the authority here, and I was just asking some very simple questions. I see how you could've taken them the wrong way...I was truly just curious about your opinion given that you know an helluva lot more about it than I.

    I don't know of any frames that would answer my first question. Seems like a good idea (except for all the issues that seem to plague e-stay bikes) but I wasn't sure if anyone did anything like that.

    For my second question, it's always cool to find out what people like you prefer. I'm a hardtail guy myself, and know very little about the differences in suspension. From an engineering standpoint, I was just wondering which you thought was the best overall.

    Thanks anyways.

  31. #31
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    Quote Originally Posted by AndrwSwitch View Post
    ^^^
    What's your background in this stuff?
    Hey mate, I'm just a young guy, trade background, that has his own fabrication/welding company, so... not much knowledge, a decent amount of experience and heaps of can do attitude Looove bikes, built 5, and out of them so far 1 Ti bike.
    Hated school, and got out of there as soon as I could, so always looking for someone else to do the research for me

    Thanks very much in pointing me in the direction of more study lol.

    I have some grade 2, 3mm plate in my shop that I was hoping would do....

    Btw, I think patents are a waste of time and money, just invented to keep lawyers and courts busy.

  32. #32
    craigsj
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    Sorry, it seemed like baiting. I like discussion but I don't like answering just to get criticized.

    Quote Originally Posted by jtmartino View Post
    I don't know of any frames that would answer my first question. Seems like a good idea (except for all the issues that seem to plague e-stay bikes) but I wasn't sure if anyone did anything like that.
    I agree with that, but it seems dependent on how you define "soft tail". There are some examples of flex plates in place of pivots, the Cannondale already mentioned and the Salsa bikes are examples. I've never seen a traditional soft tail that evolved to have a raised pivot. They could exist but I don't think so.

    Quote Originally Posted by jtmartino View Post
    For my second question, it's always cool to find out what people like you prefer. I'm a hardtail guy myself, and know very little about the differences in suspension. From an engineering standpoint, I was just wondering which you thought was the best overall.
    I think your second question is too subjective to answer. If you tolerate pedal feedback well then single pivot works. If you don't mind platform damping then you don't need a lot of antisquat, etc. I also think there are designs beyond what people have brought to market. I don't know if they would apply to XC racing since they value speed and efficiency. I'm more a trail rider and am a big believer in minimal shock platform and good anti-squat.

    I've attached an image of a design I've been working with. It uses a flex plate and flex points on the "seatstays". It also uses a progressive shock linkage like ade ward mentioned. What is radical is the very high, forward main pivot. It allows an axle path like many FR/DH bikes and enough room for a 29er with a 2.4" tire and 160mm of travel yet with a 400mm chainstay length. It uses a power pulley much like some DH bikes like, for instance, a Canfield Jedi. Anti-squat near 100% at all times.
    Attached Thumbnails Attached Thumbnails Titanium pivotless frames?-trauma.jpg  

    Last edited by craigsj; 03-11-2014 at 06:17 PM.

  33. #33
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    The limit of the flexure is the need to keep it within it's elastic limit,

    This is what in my opinion limits the travel of such a design

    But an estay design gives a longer swinging arm so for the same angle of the flexure you get more travel than a behind bb system

  34. #34
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    years ago, i designed and had fabricated a 3" travel steel soft tail. Ultimately the bike kind of sucked. It suffered from pretty bad pedal bob, and the torsional stiffness was noticably not there. It was a weird one, though, using one of the pull shocks from the early K2 razorback frames. Part of the problem was that the seat stays were at a fairly low angle which exacerbated the torsional stiffness problem. A small linkage or a more vertical seat stay helps with that. Modern pro-pedal shocks can band-aid the inherent bob problems with the standard soft tail design.

    My first had experience very much supports everything craigsj is saying. Thanks for laying it out so clearly, craigsj.

    Also, I spoke with one of the Funk guys at NAHBs, and was not impressed with his technical knowledge, but i've never ridden the bike so i won't knock it. I love the simplicity of the idea, but am clearly skeptical. I definitely think it can work, but i would even more definitely need a test ride to feel good about the purchase.

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    Ok, Grade 5 plate for the flex point. keep the service load within 50% of the max load and you have infinite cycles (pretty much).

    Ill build one in the next month, not craigsj's design (don't worry mate) because I have a different idea of my pivot places.

    But this thread has really inspired me and I see an area that has not really been explored as much as others. Cheers craigsj,

  36. #36
    craigsj
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    Quote Originally Posted by ade ward View Post
    The limit of the flexure is the need to keep it within it's elastic limit,

    This is what in my opinion limits the travel of such a design

    But an estay design gives a longer swinging arm so for the same angle of the flexure you get more travel than a behind bb system
    Yes, I agree. Also in my design, there is room for a longer flex plate which can have more range. You can also set the flex plate to be neutral at 50% travel to split the range in half. I agree, though, that flex limits of the plate and torsional stiffness of the rear end are the issues to work.

    In my design I believe the range of flex is only about 20% greater than a traditional softail at 100mm but the plate is longer. The beauty of a long single pivot is that the actual pivot point isn't too sensitive. I wouldn't build the bike at 160mm travel, either, but there's that much room for the wheel travel...

  37. #37
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    Yo dawg, I herd you like flex pivots, so we put some flex in your pivots so you can pivot while you flex:

    Flexural Pivot Bearings for Frictionless Applications - Riverhawk

  38. #38
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    This thread got me looking at pictures of some of the Castellano Designs bikes. The Fango's entire chainstay is flat. It doesn't flex much in the middle, which I think is because there's less moment than closer to the bottom bracket, but he's certainly taking the idea of a long flex plate to its logical conclusion.

    So it seems to me that there are a couple of unexplored approaches to a less crappy soft tail design.

    1) As others have said, moving the effective pivot point to somewhere other than the bottom bracket. A benefit to an actual pivot is that it can still be pretty close to the crank, just located more in line with the chain. As it gets further from the crank, gear selection on the cassette becomes more important. Too bad. But it should be relatively easy to play with the location of the pivot point. Doing something like the Nishiki Alien, but less extreme, for the chainstay location might work well.

    2) If a person designed the linkage for the seatstays to constrain lateral motion, it would help with the torsion problem.

    3) So here's an idea - a thru-axle on the back would stiffen things up some. Not a ton, it's in the wrong place, but it would force the chainstay dropouts to at least rotate together, and about a common point. So I bet there'd be some improvement. It would be tricky, because the chainstays rotate and translate in two dimensions when the suspension compresses.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  39. #39
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    I do believe that's the first time the yo dawg meme has ever been informative.
    Disclaimer: I run Regular Cycles (officialy in 2016, functionally in 2020).

  40. #40
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    Quote Originally Posted by Drew Diller View Post
    I do believe that's the first time the yo dawg meme has ever been informative.
    I'm seriously hoping you're going to attack some bamboo with a Dremel tool and come up with one of those flex pivot bearings.

  41. #41
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    On a serious note - noting how the flex pivot bearings have two orthogonal flex plates and that single flex hinges don't have much torsional stiffness, there might be some interesting possibilities of having more than one flex hinge. Which then leads to the possibility of some sort of flex VPP-type arrangement. Or of small structures that fold like origami...

  42. #42
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    Quote Originally Posted by dr.welby View Post
    Which then leads to the possibility of some sort of flex VPP-type arrangement.
    Interesting thought.

  43. #43
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    Could you explain to me in laymans terms why the pivot just behind the BB is a bad idea. I guess the forces from pedelling is in the same area, thus bobbing. If that is the case, a fixed BB and chainstay would be desirable?

  44. #44
    craigsj
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    When a bicycle accelerates due to pedaling, there are three forces that determine how the rear suspension reacts. The first force is due to the center of gravity being higher than the drive wheel. This causes the central mass to shift backward relative to the wheel creating squat. The second force is the drive wheel pushing on the frame through the pivot point and the third force is the chain itself. The idea is to create a suspension geometry that balances these forces in order to minimize suspension reactions to pedaling.

    The first force cannot be controlled very much. It is determined by the height of the center of gravity and by wheelbase. The other two forces can be controlled by the designer, although the chain force can't be controlled without using some sort of chain guide on the high tension part of the chain. BB height does effect the chain force somewhat. That leaves the drive force through the main pivot point as the primary force the designer can control.

    So to answer why the low, rearward pivot point of a softtail is bad, the force line of the drive wheel through the pivot point is far too low to balance out the squat force and the chain force can't make up the difference. The rearward part of the pivot is not so much the problem, it is the height. If you look at various single pivot designs that have evolved today, they all have heights around the location of the middle chainring. Some locate the pivot at or slightly behind the seattube while others locate it more forward near the downtube.

  45. #45
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    How about a pic?


    drivetrain forces by Andrew183, on Flickr

    The green arrow is the tension generated by pedaling in this gear combination.

    The blue and yellow arrows are the vector components of the tension, on a set of axes based on the chainstay. Add 'em up, get the green arrow.

    The blue arrow runs parallel to the chainstay. Since it gets transmitted to the chainstay by the hub, it doesn't cause bob or anything.

    The yellow arrow is the problem.

    But you can see that if you were to rotate the chainstay and the axes based on it to better match the green arrow, you could make the yellow arrow go away, or even flip it upside down. (anti-squat)

    Incidentally, this bike is what I think the ideal XC racing suspension setup is. I'd like to get a nicer one, but so far, no FS bikes have impressed me and I'd be getting a nicer hardtail.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  46. #46
    craigsj
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    Here is a diagram that was provided here by a poster I do not recall. It is not my work but I've verified that it's a correct presentation of Vittore Cossalter's explanation. It may be a bit technical for some but information isn't bad.

    You can see the three moment calculations due to the three forces I described earlier.
    Attached Images Attached Images

  47. #47
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    Quote Originally Posted by craigsj View Post
    Here is a diagram that was provided here by a poster I do not recall. It is not my work but I've verified that it's a correct presentation of Vittore Cossalter's explanation. It may be a bit technical for some but information isn't bad.
    That's tough to read but matches with what I was taught.

    The interesting thing about it is that it shows that there is not a single pivot position that provides 100% anti-squat, but actually a infinite number along a vector. Obviously, as you move the pivot back and down your axle path doesn't provide meaningful travel. But I believe this reasoning was part of the design rationale for the Cannondale Scalpel. The designers realized there were solutions located around the middle of the chainstays, and they could flex it there while having a conventional frame design everywhere else. Since it was a short travel bike, the weird axle path wasn't as big as a problem as it could be.

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    Wow, this is a really interesting subject, thanks for all this info!

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    I am thinking the neutral position of the flexure should be at the sag point, ride height with the rider on

    This is normally set at 20 to 30% of travel , but just think that a bike properly spends 99% of it's time sitting fully topped out waiting in the workshop to go out for a ride , if the neutral position was at 50% then fully topped out would be at max travel of the flexure and might over time cause the flexure to take a set
    But if set at ride height then in the topped out position it would only rest at 30%

  50. #50
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    Quote Originally Posted by craigsj View Post
    Sorry, it seemed like baiting. I like discussion but I don't like answering just to get criticized.
    Well, you have really have put some thought into it. It does look like those rear ends from the early 90's. They were called 'integrated" or some such thing. I am sure someone can help me out on that, I am having a brain fart. That is they had a very high, forward pivot.

    As far as using a flex plate. I think that is fine but it is your spring and it has to be tuned correctly for the rider at hand. I would prefer to keep my spring and damping assemblies separate so that they can be tuned. Any time you integrate the spring into the structure it is one size fits all solution.

    Also I will put forward that I don't think its long before much of this stuff is moot. Smart shocks are making their way into motorcycle racing and the like and I can see a time that all spring rates and damping rates are controlled on the fly through the shock leading to simplification of suspension designs as any number of parameters can be controlled through active damping.

    Computer controlled ferrofluidic dampers are already used on the Audi R8, corvette etc. Ohlins has a new line of computer controlled shocks for motorcycles. Give it a decade and see if it comes to MTB's

  51. #51
    craigsj
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    Quote Originally Posted by dbohemian View Post
    It does look like those rear ends from the early 90's. They were called 'integrated" or some such thing. I am sure someone can help me out on that, I am having a brain fart. That is they had a very high, forward pivot.
    Perhaps you are thinking of high pivot URTs. Dunno, but there have been some high pivots in the past. A URT needs a high pivot to avoid bob because chain tension doesn't contribute.

    There are modern examples of my pivot location but not in XC or trail bikes to my knowledge. Mostly DH stuff which sometimes gets even crazier. Have a look at the Brooklyn Machine Works SR6. In spite of its 26" wheels, it has a nearly identical pivot location and also uses a power pulley, though theirs is concentric to the pivot rather than chainstay-attached.

    Quote Originally Posted by dbohemian View Post
    As far as using a flex plate. I think that is fine but it is your spring and it has to be tuned correctly for the rider at hand. I would prefer to keep my spring and damping assemblies separate so that they can be tuned. Any time you integrate the spring into the structure it is one size fits all solution.
    The flex plate contributes to spring rate but most would still come from the shock. I've been told that the spring rate of flex plates is pretty low but I don't know myself. A design that didn't have adjustability would be a failure no doubt.

  52. #52
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    Quote Originally Posted by craigsj View Post
    Perhaps you are thinking of high pivot URTs. Dunno, but there have been some high pivots in the past...
    <a href="https://www.flickr.com/photos/benja/410660478/" title="Castellano/Ibis by benjiman, on Flickr"><img src="https://farm1.staticflickr.com/182/410660478_d6c77fe645.jpg" width="394" height="500" alt="Castellano/Ibis"></a>

    Like this 5" travel, high virtual pivot flex-plate design from the '90s? (Castellano/Ibis | Flickr - Photo Sharing!)

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