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  1. #1
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    Unvailing the King of Fat Bike Design Puzzle

    Getting two things out of the way first.

    The rear offset design of the Pugs and Moonlander...I have never been able to get my head around the reason outside of the ability to swap wheels front and rear, and it is what was handy at the time.

    If one desires to run a 29er wheelset on a fat bike, it always stuck in my mind that handling would suffer over a purpose built 29er with the same geo, due to the differences in dropout width.

    To make my point with an extreme example...lets increase the rear OLD to 10 feet. The bike would then be neigh impossible to steer...correct? It would take more input into the lean to get the same otherwise response?

    Also with a 135mm OLD up front, all the adjustments in the world to the head angle or offset would be in vain. The only saving grace would be to add weight over the front axle...a lot?

    What I am driving at is...is there something to be lost with the coming advent of 186/190 OLDs? If the above logic holds water something has to give.

    That being the case; how do you design around this...enter the Pugs and Moonlander?

    If the above logic is true is it also true that an offset rear dropout...to the right...also decreases the lean effort to the left over the right? But then comes this puzzle...it is naturally easier to lean left over right, so how are we to know just what is in play? But it also seems logical that there has to be an over riding truth regardless of what our brain says.

    What if in an offset design the drive side was moved to the left...? The larger question is how noticeable would any of this be?

    If all of the above is true does this not increase the value of an offset rear in our goal to run wider rubber?

    What say ye...to my over thinking?

  2. #2
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    Why would dropout width make handling worse? If anything it would make handling better, due to stiffness.

    Why would dropout width affect head angle and trail? the width of the dropouts affects neither the trail or head angle, where as, the trail and head angle do affect each other when you change one of them.

    Are you sure you're not high? I mean, why is it naturally easier to lean left than right? That's nonsense, everyone is different.

  3. #3
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    Quote Originally Posted by Sand Rat View Post


    What say ye...to my over thinking?


    ...you are over thinking.

  4. #4
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    I think that either, I am confused, or you are confused. Could you perhaps clarify your thoughts to alleviate my confusion? I don't see any reason that wide hubs or offset design would affect the handling. The centreline of the wheel is still in line with the centreline of the bike.

    Bikes of yore tried drive trains on the left and it works jsut fine, but the right side drive train became standard. I don't think that any of that makes any real difference to riding. I am more comfortable leaning left than right, but that is individual. Some will be more comfortable to the right. But even still the difference for me is negligible.

    I'm still confused

  5. #5
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    Quote Originally Posted by stoney bones View Post
    ...you are over thinking.
    +1

    Hub width does not affect handling except where it might increase weight or stiffness. The width itself is not part of the handling or fit geometry.
    Offset vs symmetric also does not affect handling beyond what effect it might have on wheel stiffness.
    A fatty 29er may suffer some compared to a designed 29er but not because of the hub width. It is because of compromises needed to clear the fat tires. Particularly using 100mm bottom bracket and extra wide chain stays. But these are mostly ergonomic issues not handling issues.
    Building a 29er wheel on an offset hub does involve some compromises because the wheel must be dished to accommodate the offset. The Moonlander 28mm offset is probably beyond what you can do with 29er rim.

    Craig

  6. #6
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    Important fact about offset:

    The wheels are still in line. *

    There is a growing myth perpetuated by internet experts that there is a difference in handling with the Pug because of the offset. There is not. The wheels are not offset.

    Only the chainstays and the hub are offset.

    The tyre and rim are centred with the bike.

    There is no effect on the handling from the offset.

    (*Edit: sorry about the emphasis, but I have seen posts in various threads and forums about this offset "problem" a number of times and I think it needs to be laid to rest)
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  7. #7
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    The ability to swap front and rear wheels is not the main reason for the offset design. Rather, it's to allow the chain to clear the tire with a standard 135mm rear hub. Because the hub is not centered in relation to the rim, the asymmetrical frame becomes necessary to center the rim in relation to the main tubes of the frame (and the rider). An asymmetrical fork and offset front wheel are not required at all.

  8. #8
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    To the OP: From what I gather of your overall understanding of bicycle dynamics, you should just revert to listening to the advice of those with experience, and when it comes to concepts of offsets, and asymmetrical designs, just trust us all that all of the designs out there work great for what the manufacturers are suggesting they be used for.

    as far as finding the right bike for what you want to do, I would suggest just stating what you want to do with the next bike you might get in a thread, and try the bikes suggested on a trail if possible, and not worry at all about what numbers are involved in the geometry, or what the bike looks like.

  9. #9
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    The real puzzle to me is how to cope with increasingly fat tires, feet, cranks, and chainrings all sharing the same real estate.

    What you get from symmetry is some weight optimization, at the expense of narrower range of component choices.

    People are happily riding Lefty forks, which are the definition of offset and asymmetrical. And those have moving parts.

    You get what Velobike emphasized though, yeah? The rubber meets surface directly under your butt.
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  10. #10
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    On the idea of wider hubs affecting handling, iwould say that a 29er wheelset built with 170mm, and 135mm hubs would handle better due to stronger stiffer wheels, and that for heavier stronger riders, I would suggest them even on a 29er without fat tires. I have destroyed a 100mm hub 29er wheel from riding too fast through a turn without even hitting anything but smooth dirt.
    I think 135mm front forks should be specified on 29ers for clydesdale type riders.

    and as far as 17.5mm offset 135mm 29er wheels, a rear wheel probably has less dish(more even spoke tension) than a standard 29er geared rear wheel, as the rim is dished to the opposite side from normal.
    Last edited by autodoctor911; 04-18-2013 at 03:22 PM.

  11. #11
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    Post...go to work...return...check in...Thanks Guys!

    Not sure if my failure to follow some is due to them not following...me. Perhaps due to the limits of the internet...that sounds safe!

    Let me try it from a different angle. Longer trail...does what? A longer stem...does what?
    A longer bar does...what? Why would not a wider (longer) axle have the same effect?

    I get that regardless of the design, the wheels are by necessity centerlined. The wheel, the contact patch is like a fulcrum point for the axle. The Axle is like a plank on a teeter totter, or a lever if you will. In effect, if you try to do a one man balance act on a teeter totter, say your feet are fixed equal distant from the fulcrum point.

    The wider the symmetrical dropout, the farther apart your feet. An offset design affords a closer stance, at the expense of being asymmetrical to the fulcrum point. This poses an adjustment in the balance act, but I see it as being neutral overall in affect, just different.

    If 6" tires are produced, what are we looking at...206 hubs and 150's with 28mm offset? It is just that it boggles my mind to think that hub width can change in a vacuum with regards to feel of handling.

    My aim in this thread is to explore, what ever the facts are is what they are, understanding the forces at work better is the goal. Which brought about the question; With hub widths at an extreme, would it be a mistake to believe that a 29er set would prove just as satisfactory as in a frameset built for 4" tires?

    As for the left turning thing...oval track racers go in what direction? Why? If by default of choice, I submit there is a reason behind that choice by default though unstated and unrecognized.

    And no offence meant...I don't trust anyone who says..."Trust Me" I am not concerned with adhering to convention if I see it as to my advantage to buck it..."Trust Me" LOL

    Please feel free to jump in with more comments.

  12. #12
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    Re: Unvailing the King of Fat Bike Design Puzzle

    A wider hub does not necessitate any geometry or ergo changes.
    If tires get much wider you will need wider bottom bracket which will affect ergos.
    135 Offset frames and 170 frames use the same BB size and usually same chain stay length.

    Craig

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  13. #13
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    The Dude abides.

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    Re: Unvailing the King of Fat Bike Design Puzzle

    If it helps think of bicycle geometry as 2d. That is the only dimensions that affect handling.
    The axle is just a point on the 2 D plane. Width does not matter.
    It may affect wheel and frame stiffness.

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  15. #15
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    There are a lot of variables affecting fatbike handling.

    Skinny bikes don't have so much variation in tyre size, tyre pressures and rim size. On a fatbike, change just one of those factors and you have a different handling bike.

    I'm not keen on the current crop of 135mm forks. We're still using axles with a diameter designed for the size of tyres they had in the 1890s, and yet a fatbike has tyres the size of a motorbike with the resultant feedback into the frame. I would like to see large diameter axles on fat forks and until then I'll stick to as narrow as possible, ie 100mm.

    The most precise handling I've found is when I had a very steep head angle which is contrary to the more accepted view, but that was only tested with a narrow range of tyres and rims.

    I suspect the most important factor may not be trail or head angle but the combination of flop and the tyre profile (ie how rim size affects tyre shape). I'll probably get round to testing that some time this year.
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  16. #16
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    Topicstarter has a point, but there are some things that don't make sense

    There is such a thing as stiffness of the frame!

    A wider beam is a stiffer (and stronger) beam unless you use a stronger or more material!

    So, much less frame torsion when you pedal, but also in corners etc.

  17. #17
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    Quote Originally Posted by Velobike View Post
    There are a lot of variables affecting fatbike handling.

    Skinny bikes don't have so much variation in tyre size, tyre pressures and rim size. On a fatbike, change just one of those factors and you have a different handling bike.
    Bar width and stem length can be tweaked to adjust steering feel...are not contact patch width and axle length much the same? A bike is also steered through the seat no?

    A concern that I have is that as axle width at the rear is increased while the front remains constant is that there could be a pushing effect generated on the front which could be adverse.

    I do not foresee any proof for my concerns forthcoming unless an engineer can bring clarity. But until then...forewarned is fore armed? If any possible downside is outweighed by whatever upside for a given individual...then go for it...you now have the tools to make a better choice?

    Take Beth...with her experience with her mishaps...what I took away for myself is that at my age, it might be best to stick to fat tires alone. Going from fat to skinny, opens myself up to overlooking possible hazards due to a change in tire width. It could end my riding days at worse and in any event it now takes longer to recover, the risks outweigh the benefits.

    So that's where I am at with all of this...thanks to all for being there to prod me on.

  18. #18
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    Quote Originally Posted by Sand Rat View Post
    Bar width and stem length can be tweaked to adjust steering feel...are not contact patch width and axle length much the same? A bike is also steered through the seat no?...
    Yes, you can change the feel and a good setup can mask imperfect geometry up to a point. The human body is incredibly adaptable and with a bit of practise you can ride what seemed unrideable. Which is why we can have different fashions in bike configuration and geometry from decade to decade instead of an absolute fixed design. For an example find an old upright bike with rod brakes and try riding it on singletrack. Feels all wrong, but that's what our ancestors were on 100 years ago and riding them around the world on dirt roads.
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  19. #19
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    There is merit in the OP, if not ultimate clarity. It does do good to reflect on the idea offered, if not the surmise, and to look further for answers.

    Quote Originally Posted by Velobike View Post
    There are a lot of variables affecting fatbike handling.

    Skinny bikes don't have so much variation in tyre size, tyre pressures and rim size. On a fatbike, change just one of those factors and you have a different handling bike. I suspect the most important factor may not be trail or head angle but the combination of flop and the tyre profile (ie how rim size affects tyre shape). I'll probably get round to testing that some time this year.
    I am thinking that I agree. I noted a distinct self steer on my first Fatty. This was something I have not really encountered before, at least to this degree. I was trying to figure out what exactly was causing it, especially since I was the one building the frames, and as such, always seeking to improve the "product." My own thinking and experience since, added to those of others on this forum, has lead me to believe that the tire is the single largest factor in handling.

    I have very recently come clear to the notion that some of what I was feeling was simple gyroscopic effect, and it has become quite noticeable to me now that I have separated it from other phenomena. The simple fact that you have all that added mass out there spinning about its axis explains that neatly.

    So too do I believe that the width of the tire is a larger lever acting upon the steering, in a radial sense. The extra width of the tire gives surface grip far outside the width of a normal MTB tire, and my thinking is that this is also responsible for some of the pull felt at the bar. Add to that the notion that the tire certainly is deforming away from the centerline of the wheel under these loads (see attached), and it seems that the effect would be further magnified.

    Tire pressure of course has something to do with that, but in my experience I'm thinking that takes a back seat to tread design. It has been noted by many, including myself, that the HuDu is very prone to self steer, where you do not necessarily hear that about the Nate; a tire with a decidedly more aggressive tread. This mirrors my experience.

    I'm not keen on the current crop of 135mm forks. We're still using axles with a diameter designed for the size of tyres they had in the 1890s, and yet a fatbike has tyres the size of a motorbike with the resultant feedback into the frame. I would like to see large diameter axles on fat forks and until then I'll stick to as narrow as possible, ie 100mm.
    Are you taking exception based on perceived structural weakness, or do you feel that you can actually sense too much flex from the wider hubs? I also am not overly enthused by not having the option of some sort of through axle for the front, and if I were smart enough to figure out how to get one of these new 12mm T/A rear hubs on the front, I'd do it. No, I've never broken a skewer, but at the same time, it sure SEEMS impossibly frail.
    Attached Thumbnails Attached Thumbnails Unvailing the King of Fat Bike Design Puzzle-tirewidthcomparison.jpg  

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  20. #20
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    Quote Originally Posted by Sand Rat View Post
    Post...go to work...return...check in...Thanks Guys!



    I get that regardless of the design, the wheels are by necessity centerlined. The wheel, the contact patch is like a fulcrum point for the axle. The Axle is like a plank on a teeter totter, or a lever if you will. In effect, if you try to do a one man balance act on a teeter totter, say your feet are fixed equal distant from the fulcrum point.

    The wider the symmetrical dropout, the farther apart your feet. An offset design affords a closer stance, at the expense of being asymmetrical to the fulcrum point. This poses an adjustment in the balance act, but I see it as being neutral overall in affect, just different.

    If 6" tires are produced, what are we looking at...206 hubs and 150's with 28mm offset? It is just that it boggles my mind to think that hub width can change in a vacuum with regards to feel of handling.

    Please feel free to jump in with more comments.
    I think one of your mistakes is to think that the fulcrum of your teeter totter moves over as the hub is offset to the side. The balance point or fulcrum is the tire contact to the ground. Your connection is your feet on the pedals. The connection between those two points does not matter as long as it is rigid. Obviously if the connecting structure is made super wide so it hits the ground as you lean that would be a problem and if it was offset way to one side so there was lots more mass on one side that could be a problem. At the sizes we are talking about between a 29er wheel and a fat wheel it does not matter.
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  21. #21
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    Keeping all other variables the same, axle width has no affect on handling, other than making the wheel build stiffer and possibly improving handling.

    You do have to be careful about helmet width though. Wider helmet will make your steering slower.

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    You can't throw axle length in with the stem or bar length changes. By changing bar or stem length you are changing the distance from the axis of rotation which affects leverage and handling. No matter how wide the axle is, as long as the wheel is still centered there is no change about the axis of rotation.

  23. #23
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    Re: Unvailing the King of Fat Bike Design Puzzle

    This seems like a troll effort. Fun reading,though!

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  24. #24
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    Quote Originally Posted by tfinator View Post
    This seems like a troll effort.
    After looking at Sand Rat's post history, I disagree.
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  25. #25
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    Quote Originally Posted by TrailMaker View Post
    ...Are you taking exception based on perceived structural weakness, or do you feel that you can actually sense too much flex from the wider hubs?...
    I've tried 3 different 135mm forks. On each of them heavy braking produced an element of instability which was not obvious on the 100mm fork. The best description I can give of it was that I was feeling squirm.

    I haven't done any measurement comparison of the actual (if any) flex for the various forks/wheel combinations, so this is just an opinion. If someone was to do this it would be an interesting comparison.

    The likes of a truss fork may compensate for inadequacies in the axle.

    In the meantime I'll stick to narrow OLDs if possible.

    Quote Originally Posted by tfinator View Post
    This seems like a troll effort. Fun reading,though!...
    No, it's a point worth raising. Sand rat likes to philosophise.
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    Re: Unvailing the King of Fat Bike Design Puzzle

    Sorry, I didn't look at post history, but comparing the width of a hub to the length of a stem... apples to oranges, ya know?

    Philosophize on!

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  27. #27
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    I think it may help to just consider that in the see-saw comparison, the plank changes angle with respect to the person standing on it.

    On a bicycle, even with suspension, the axles always stay square to the bike, save for a little flex in the frame, and despite Velobikes observation about forks, which I will talk about in a second, usually stiffness of the frame is not significantly compromised by widening axles to the point where handling is affected.

    If you assume the frame is sufficiently stiff, when you look at bicycle handling, the only things moving in relation to each other are the handlebars, stem, fork, and front wheel. when you put a rider on it, there is also the change in center of mass based on where the rider is leaning. The width of the pedals(and their minimum hieght) is a consideration as far as lean angle while pedaling, and if the rider is standing, the amount of leverage you have to lean to one side of the bike, but the width of the axles does not play a role.

    the rider and his weight changing location to change the center of mass is not essential to the handling or stability of a bike. Most riders do not realize it, but when you are leaning the bike into a turn, you are doing so with the steering input, not by leaning your body. When a rider initiates a turn, he initialy turns the bars away from the turn, which causes the bike to lean into the turn, then the rider turns the front wheel back toward the turn to keep the movement such that the angular acceleration of the turn keeps the leaning bike from falling over. Then to straighten out, he turns sharper into the turn, which brings the bike upright, while straightening out the front wheel again to resume straightline motion. Trail and head angle are what make this happen. The whole process seems counter intuitive. No one who learns to ride a bike even realizes what motions are doing what, it just becomes part of your body's natural instincts to where you think you are actually leaning the bike over, not steering it to do so.

    For proof, look at a remote control motorcycle. It has no moving mass to simulate a rider leaning.

    for further information on this subject I recommend reading the wikipedia article:Bicycle and motorcycle geometry - Wikipedia, the free encyclopedia

    To Velobike: do you think the weakness of the 135mm forks you have used is due to the distance of the braking surface from the center of the forks causing a greater leverage for twisting. A through axle would definitely help some in this respect, and a double crown even more so. Or you could run two front brakes.

    I do notice a lot of flex with braking on the Onone fat front fork, but I haven't noticed anything when not looking directly at it, and while I do watch it it seems to stay straight, with the non brake side flexing just as much.

    As to forces other than braking, twisting forces should be less with the wider axle, since you have less of a leverage difference between the tire radius and the hub width, which should make up for any additional flex at the wider crown area, whic is going to be more flexible on a fat fork, no matte what the axle width.
    Last edited by autodoctor911; 04-19-2013 at 04:20 PM.

  28. #28
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    For those who struggle with trying to understand my points, and me yours...I did rather poorly in Physics class... Keep posting...maybe...just maybe...

    VB may have a little trouble wading through my writings also...but he understands ME quite well...so thanks to him and Drew.

    BY the way VB, given any thought to the suggestion by CK of a Blog?

    Sasquatch141...Your comment about helmet size...larger auto adjusts everything to just perfect!

    Nothing's Impossible...Was that you at a previous UK gathering? Going to make the upcoming one? I dare say that you have a brain worth picking when it comes to balance and control on a bicycle.

    Sryanak...With the teeter totter idea and my feet. My feet were fixed and representing the axle end points. In the front, steering takes place in a horizontal plane, in the rear, on a vertical plane through the seat, was the idea I was trying to convey. Therefore my thought that axle width like bar width does matter. The handle bar is nothing more than an indirect connection to the front axle. In the rear, the seat is your connection to the rear axle, but if standing, then the pedals are that connection as you say.

    I keep thinking...axle length...range of motion...longer means stable, slower = an affect that has be produce an effect. For every action there is an opposite and equal reaction.

    But if your head hurts like mine...don't worry about me, this is not life or death.

    Not sure if that makes things better or worse, like I say...Physics not my strong suit. If you can say we agree, great, but I remain unsure.

    So post away...even if I should go quiet on this thread for awhile, know and rest assured that I am reading and tucking away your points/thoughts until such time as I can assemble them into a better understanding. Who knows...sometimes I find that someone says something just a little different at the right time...and things just fall into place.

    Who knows, TrailMaker may be helped more than I by something said.

  29. #29
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    Quote Originally Posted by autodoctor911 View Post
    To Velobike: do you think the weakness of the 135mm forks you have used is due to the distance of the braking surface from the center of the forks causing a greater leverage for twisting. A through axle would definitely help some in this respect, and a double crown even more so. Or you could run two front brakes...
    Yes, that's my conclusion.

    I thought about the 2 front brakes - gave it all of 10 seconds. Too much faff for me.
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    Would like to hear from those up in Alaska who are working on the development of the reported 186/190 standards to see what their thoughts are.

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    I just did another fork flex test on the Fatty fork by holding the brake locked and pushing the bike forward, while My assistant holds a straight edge on the fork legs and measures the deflection, and I can't get the left(brake) side to flex any more than the right side. they are both deflecting about a half inch when I use one foot on a pedal to hold the rear heel down, and the other to push forward (backwards against the ground), and both hands on the bars with only the front brake applied at full squeeze.

  32. #32
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    Quote Originally Posted by autodoctor911 View Post
    I think it may help to just consider that in the see-saw comparison, the plank changes angle with respect to the person standing on it.

    On a bicycle, even with suspension, the axles always stay square to the bike, save for a little flex in the frame, and despite Velobikes observation about forks, which I will talk about in a second, usually stiffness of the frame is not significantly compromised by widening axles to the point where handling is affected.

    If you assume the frame is sufficiently stiff, when you look at bicycle handling, the only things moving in relation to each other are the handlebars, stem, fork, and front wheel. when you put a rider on it, there is also the change in center of mass based on where the rider is leaning. The width of the pedals(and their minimum hieght) is a consideration as far as lean angle while pedaling, and if the rider is standing, the amount of leverage you have to lean to one side of the bike, but the width of the axles does not play a role.

    the rider and his weight changing location to change the center of mass is not essential to the handling or stability of a bike. Most riders do not realize it, but when you are leaning the bike into a turn, you are doing so with the steering input, not by leaning your body. When a rider initiates a turn, he initialy turns the bars away from the turn, which causes the bike to lean into the turn, then the rider turns the front wheel back toward the turn to keep the movement such that the angular acceleration of the turn keeps the leaning bike from falling over. Then to straighten out, he turns sharper into the turn, which brings the bike upright, while straightening out the front wheel again to resume straightline motion. Trail and head angle are what make this happen. The whole process seems counter intuitive. No one who learns to ride a bike even realizes what motions are doing what, it just becomes part of your body's natural instincts to where you think you are actually leaning the bike over, not steering it to do so.

    For proof, look at a remote control motorcycle. It has no moving mass to simulate a rider leaning.

    for further information on this subject I recommend reading the wikipedia article:Bicycle and motorcycle geometry - Wikipedia, the free encyclopedia

    To Velobike: do you think the weakness of the 135mm forks you have used is due to the distance of the braking surface from the center of the forks causing a greater leverage for twisting. A through axle would definitely help some in this respect, and a double crown even more so. Or you could run two front brakes.

    I do notice a lot of flex with braking on the Onone fat front fork, but I haven't noticed anything when not looking directly at it, and while I do watch it it seems to stay straight, with the non brake side flexing just as much.

    As to forces other than braking, twisting forces should be less with the wider axle, since you have less of a leverage difference between the tire radius and the hub width, which should make up for any additional flex at the wider crown area, whic is going to be more flexible on a fat fork, no matte what the axle width.
    You know, while riding motorcycles I just realized that my attention has never been on what the bars and front wheel are doing, my attention was on the more drastic shift of body weight...on the lean. There is also the power distraction a motorcycle has over a bicycle. As a result when on a bicycle, less attention was/is paid.

    I think you have said more in a complete manner that gives it to me in bite sizes. Thanks.

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    thanks to drew and velo, who made me realize it might not be hopeless to try and explain some of the dynamics to you.

    From the first post I thought you might not be able to grasp it.

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    Quote Originally Posted by Sand Rat View Post
    .

    I keep thinking...axle length...range of motion...longer means stable, slower = an affect that has be produce an effect. For every action there is an opposite and equal reaction.
    The flaw in this logic is you aren't standing on the ends of the axle. If your input was just to the axle ends then yes you have to move the end of a longer axle more to move the wheel. However they are rigidly connected to the rest of the frame. No matter how wide the rear hub move the head tube one degree and the rear tire moves the same ratio of that amount.
    Or to put another spin on it. Think about it this way. On an offset frame one end of the axle is closer to the centerline then the other. If a wider bike behaved differently than a narrower bike then the two halves of an offset frame would behave differently relative to each other and the bike would have to explode. Since they are all rigidly connected the short end gets a bit less input and gives back a bit less and the long end gets a bit more and gives back a bit more and by the time you get to the centerline of the bike over the tire the input is the same from both sides. I wish I could explain this better.
    Latitude 61

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    Quote Originally Posted by Velobike View Post
    I've tried 3 different 135mm forks. On each of them heavy braking produced an element of instability which was not obvious on the 100mm fork. The best description I can give of it was that I was feeling squirm.

    I haven't done any measurement comparison of the actual (if any) flex for the various forks/wheel combinations, so this is just an opinion. If someone was to do this it would be an interesting comparison.

    The likes of a truss fork may compensate for inadequacies in the axle.

    In the meantime I'll stick to narrow OLDs if possible.
    So...

    You are feeling a radial rotation without bar movement? Squirm would be a good descriptor there. Hmmm... Perhaps I have not refined my experience that far, but I can't say I've notice that. I definitely notice a fair amount of flex under heavy braking, as you say. Since I am a biggun and use an 8" rotor, it is pronounced. What I'm trying to decide is if the fork is exacerbating the brake shudder, both audibly and tactiley. Perhaps even causing it, or perhaps more accurately allowing it to occur.

    You feel the narrower axle width is more stable? Hmmm...
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    Quote Originally Posted by sryanak View Post
    If a wider bike behaved differently than a narrower bike then the two halves of an offset frame would behave differently relative to each other and the bike would have to explode.
    The part about each side behaving differently I understood, but I was failing to grasp what that would result in...something broken! So of course it follows my supposed premise was wrong.

    Thanks to Autodoctor, what he said, jarred my stuck in the rut thinking. I was going through all sorts of injustice to logic. In time, I shall go over all that has been said by yourself and others and attempt to untwist things. But your above statement drove the nail home, sealed the coffin on a misguided concept.

    Thank you for your efforts.

    Mike

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    Quote Originally Posted by Sand Rat View Post
    You know, while riding motorcycles I just realized that my attention has never been on what the bars and front wheel are doing, my attention was on the more drastic shift of body weight...on the lean. There is also the power distraction a motorcycle has over a bicycle. As a result when on a bicycle, less attention was/is paid.

    I think you have said more in a complete manner that gives it to me in bite sizes. Thanks.
    For the most part, on a bicycle, or motorcycle the body weight does not shift at all. It's tilted in perfect harmony with the bike due to the forces created by turning the front wheel. Just watch someone else riding right in front of you, and follow them through a turn. You will notice that their spine stays pretty straight with respect to the bicycle. It does not feel so to the rider because the feel you have for riding balance, is intertwined with the movement of the bike. Usually it is learned at a young age, which makes the motions even more embedded into your muscle memory.

    If you were to lean to the left with your body while holding the bars straight, you would actually lean the bike to the right, making the bike want to turn right. You can test this by riding the bike with no hands, or better yet, push the bike with your hand on the seat. the bike goes the direction the seat goes, which is opposite the way your upper body leans.

    Usually the only time you lean very much to the side on a bicycle is at slower speeds to turn a tighter radius, and even then, it's not much movement.

    On a motorcycle though, at higher cornering speeds, when the limit of the lean angle is reached due to ground clearance, the rider can move to the inside of the turn to balance the bike as lateral forces try to tip the bike over to the outside of the turn(high siding)

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    Quote Originally Posted by TrailMaker View Post
    So...

    What I'm trying to decide is if the fork is exacerbating the brake shudder, both audibly and tactiley. Perhaps even causing it, or perhaps more accurately allowing it to occur.

    You feel the narrower axle width is more stable? Hmmm...
    Are you saying that the shudder is at the pads or in the fork? My impulse is to suggest that there may be a cause and effect cycle going on. The fork flexes, springs back, and until you release the pressure, the cycle repeats?

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    [QUOTE=autodoctor911;10333541]For the most part, on a bicycle, or motorcycle the body weight does not shift at all. It's tilted in perfect harmony with the bike due to the forces created by turning the front wheel. Just watch someone else riding right in front of you, and follow them through a turn. You will notice that their spine stays pretty straight with respect to the bicycle. It does not feel so to the rider because the feel you have for riding balance, is intertwined with the movement of the bike. Usually it is learned at a young age, which makes the motions even more embedded into your muscle memory.



    As you are pointing out, my use of descriptions are misplaced, and you give the reason. Perception alone can not be used to define reality, but we tend to govern our lives through it.

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    Quote Originally Posted by autodoctor911 View Post
    For the most part, on a bicycle, or motorcycle the body weight does not shift at all. It's tilted in perfect harmony with the bike due to the forces created by turning the front wheel. Just watch someone else riding right in front of you, and follow them through a turn. You will notice that their spine stays pretty straight with respect to the bicycle. It does not feel so to the rider because the feel you have for riding balance, is intertwined with the movement of the bike. Usually it is learned at a young age, which makes the motions even more embedded into your muscle memory.

    If you were to lean to the left with your body while holding the bars straight, you would actually lean the bike to the right, making the bike want to turn right. You can test this by riding the bike with no hands, or better yet, push the bike with your hand on the seat. the bike goes the direction the seat goes, which is opposite the way your upper body leans.

    Usually the only time you lean very much to the side on a bicycle is at slower speeds to turn a tighter radius, and even then, it's not much movement.

    On a motorcycle though, at higher cornering speeds, when the limit of the lean angle is reached due to ground clearance, the rider can move to the inside of the turn to balance the bike as lateral forces try to tip the bike over to the outside of the turn(high siding)
    Hmmmm....

    I have to disagree with a lot of this. Not all, but a lot. The dynamics of this are extremely complex and variable, and hard to elucidate, and the actions of the rider are extremely subtle. Perhaps not even visible in your following-rider scenario, and that is all it takes to initiate a turn on a two wheeled vehicle much of the time. The amount of force necessary to initiate a turn varies depending on the mass and speed of the vehicle in question, and very likely stays proportional to that, but it takes very little to tip a two wheeled conveyance to one side.

    So, to turn a bike right, you are saying the rider leans left? I don't think anyone rides like that. A bike goes where the mass goes. If you had no steering, the only way to change direction would be to lean in the direction you wanted to go. Obviously, with no steering, at that point you would have very little control of the change in direction, and would fall to the ground on the side you leaned to. Steering is a wonderful thing.

    That's a start.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
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    Quote Originally Posted by TrailMaker View Post
    Hmmmm....

    I have to disagree with a lot of this. Not all, but a lot. The dynamics of this are extremely complex and variable, and hard to elucidate, and the actions of the rider are extremely subtle. Perhaps not even visible in your following-rider scenario, and that is all it takes to initiate a turn on a two wheeled vehicle much of the time. The amount of force necessary to initiate a turn varies depending on the mass and speed of the vehicle in question, and very likely stays proportional to that, but it takes very little to tip a two wheeled conveyance to one side.

    So, to turn a bike right, you are saying the rider leans left? I don't think anyone rides like that. A bike goes where the mass goes. If you had no steering, the only way to change direction would be to lean in the direction you wanted to go. Obviously, with no steering, at that point you would have very little control of the change in direction, and would fall to the ground on the side you leaned to. Steering is a wonderful thing.

    That's a start.
    I think AutoDoc misspoke a little, while trying to make a point, he knows that no one does ride as per his example.

    If one were to lean left while keeping the bars straight, the bike mass and rider mass are then not in the same plane, the mass of the bike is at the riders right, but the direction in which the bike goes, it seems to me, to be governed by what mass is able to exert the greater force upon the direction of travel. If bike mass is greater, and rider mass so light, the bike will remain in the same direction of travel, but such not being the case, the bike follows/turns with the mass of the rider with the bars remaining straight.

    So I would agree with you.

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    Further;

    If it is a lean-initiated turn, which most turns are - and again it takes an almost imperceptible amount to accomplish this most of the time - the rider then "catches" the tip-in of the bike by steering. When the front wheel is steered enough - and a turn radius of proper length is achieved - that steering input counters the tip in. Steer too little and the tip-in continues to whatever varying degree. Steer too much, and the bike either straightens to some degree or the front wheel folds under and you lose some skin! We learn - as The Doc suggests - from experience and repetition until it becomes an ingrained proportion that we manage without even thinking about it.

    The thing that makes this really tricky is there is an infinitely variable degree to which each action effects the outcome. This makes it very hard to explain it in absolute terms.
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    Quote Originally Posted by Sand Rat View Post
    Are you saying that the shudder is at the pads or in the fork? My impulse is to suggest that there may be a cause and effect cycle going on. The fork flexes, springs back, and until you release the pressure, the cycle repeats?
    Ooops, forgot;

    I think it is clear that the brake is initiating the issue. I am wondering if the fork is exacerbating it. I believe that it likely is. I do not have this problem with my suspended bikes, but both of my Fatties with Enable forks do it. One bike each of both suspended and Fat bikes share the same brake system; two with Hayes Nine, and two with Strokers.
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    One factor I only thought about today - strangely while cycling a 60 year old bike up a really steep hill.

    The 135mm hub I used may not have as good an axle as the 100mm.

    That's another potential explanation.
    As little bike as possible, as silent as possible.
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    Quote Originally Posted by TrailMaker View Post
    Further;

    If it is a lean-initiated turn, which most turns are - and again it takes an almost imperceptible amount to accomplish this most of the time - the rider then "catches" the tip-in of the bike by steering. When the front wheel is steered enough - and a turn radius of proper length is achieved - that steering input counters the tip in. Steer too little and the tip-in continues to whatever varying degree. Steer too much, and the bike either straightens to some degree or the front wheel folds under and you lose some skin! We learn - as The Doc suggests - from experience and repetition until it becomes an ingrained proportion that we manage without even thinking about it.

    The thing that makes this really tricky is there is an infinitely variable degree to which each action effects the outcome. This makes it very hard to explain it in absolute terms.
    I beg to differ. When we "lean" in to initiate a turn, we are leaning with the steering. Yes, you apply more weight to the hand on the inside of the turn, but it is the slight turn of the handlebars in the opposite direction when you do so that leans the bike and yourself over. You are right that it is a very subtle action, but it is the input to the bars that initiates the turn in most cases. If you were to initiate a turn by leaning your body, the bike will definitely move to lean the opposite direction from your body more than you think.
    Steering input is what keeps the bike balanced under you in the first place. A bike with no steering us unrideable.

    try focusing on your stem when standing up and riding(in a safe wide open place), then try to lean into a turn and not let the stem cross the centerline away from the turn.
    You can do it, but you have to lean the bike into the turn, while your body stays upright, and even then, the steering is actually crossing the centerline slightly, or you would fall over.
    Now, try the same thing while seated. You will find that if you cannot turn the front wheel to the right, for example, it is impossible to turn left, or even to go straight, and not fall over for that matter.
    Yes, this sounds wrong. It is not what it feels like you are doing when you lean a 2 wheeled vehicle over, but if you pay close attention to the angle of the stem when initiating a turn, you can observe how necessary it is to steer away from a turn in order to lean into it.
    Last edited by autodoctor911; 04-20-2013 at 02:22 PM.

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    Hey;

    I need to make sure I am reading you correctly. Are you saying that turns are initiated by steering away from the intended direction, causing the tip in, and then caught with the correct amount of steering into the turn?
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
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    yes

    That is an excellent way of stating it. brief, yet fully descriptive of the process.

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    OK;

    Well, I do not really believe that is the way most people initiate a turn on a bike. I believe it is done with a very subtle shift of the hips. I just went out in the street and tried it all, just to make sure. How many people really think about it... really? I had to make sure... again. I don't turn a bike that way. I turn by leaning and then catching the fall with the bars.

    Do I believe a turn CAN be initiated by steering away? Yes. It is a concept I am very familiar with from years of track driving and instructing in cars. It is a very common practice there, called "shaking" the car for those not aware of it, and comes in very handy when you have a car that is reluctant to set the front end into a turn for whatever varying reason. In Rallying, it is virtually the ONLY way to make a car pivot around a turn, particularly in low grip or super tight radius situations. Hence the name, "Rally Turn."

    However, in bikes there is no CG (center of gravity) in the horizontal plane effecting how they turn. There is no need to swing the mass of the conveyance around this CG to get it to rotate. There is no rotation at all. There is simply vertical fall and catch. I can indeed shake the bike and make it turn, but it is really quite unnatural to me. If there is any slight turn of the front wheel away from the turn, I think it is merely sympathetic.

    That's my take on it.
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    "Sympathetic"? Did you try to turn without doing it?
    It's not a matter of personal preference, it's the way a two wheeled vehicle behaves.
    I also race cars, and the "shaking" you refer to has nothing to do with what is going on on a bicycle, But moving the Cog in the horizontal plane is quite important in turning a 2 wheeler. when you initiate the turn by turning the front wheel slightly away, the Cog being above the contact patch of the front tire is what causes the bike and rider to lean over with the force of inertia acting as a lever against the force vector created by the front tire. once the mass is leaning over, the front tire must change direction to keep the rider and bike upright. this happens constantly while riding straight to keep you upright.

    when turning, you are letting that slight steering angle back and forth go unbalanced to one side, just long enough to lean over, then you have to steer more drastically to catch it from falling over, at which point you are leaned over with that Cog being accelerated to the side with enough force to balance the pull of the earth.
    Notice that to resume riding stright, you must turn the front wheel more sharply into the turn to bring you and the bike upright. it is basically the same thing you did to start the turn in reverse.
    You don't have to be convinced by me or trust me. To verify this you can just read through the article I referenced earlier, or better yet this one:
    Bicycle and motorcycle dynamics - Wikipedia, the free encyclopedia

  50. #50
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    see also:
    Countersteering - Wikipedia, the free encyclopedia

    quotes from article above:
    At low speeds countersteering is equally necessary, but the countersteering is then so subtle that it is hidden by the continuous corrections that are made in balancing the bike, often falling below a just noticeable difference or threshold of perception of the rider. Countersteering at low speed may be further concealed by the ensuing much larger steering angle possible in the direction of the turn.
    Unthinking behavior
    Countersteering is indispensable for bike steering. Most people are not aware that they employ countersteering when riding their bike any more than they are aware of the physics of walking. They have learned to apply the required countersteering without thinking.
    As is well known in bicycle racing, the countersteering phenomenon becomes evident when there is an obstacle preventing the wheel from countersteering (e.g., when closely overlapping wheels or riding very close to a curb). In these situations, the way to initiate a turn with the handlebars away from the obstacle is to countersteer towards obstacle to avoid crashing into it.[13] Lack of understanding of this principle leads to accidents in novice bicycle races.
    Motorcycles

    Even more so than on a bicycle, mastering the technique of consciously countersteering is essential for safe motorcycle riding, and as a result is a part of the safe riding courses run by the Motorcycle Safety Foundation and the Canada Safety Council. At the higher speeds that motorcycles commonly attain, it becomes increasingly impractical to steer by taking advantage of the minute and random corrections needed to maintain balance.
    Much of the art of motorcycle cornering is learning how to effectively "push" the grips into corners and how to maintain proper lean angles through the turn. When the need for a quick swerve to one side suddenly arises in an emergency, it is essential to know, through prior practice, that the handlebars must be deliberately pressed away on that side instead of being pulled. Many accidents result when otherwise experienced riders who have never carefully developed this skill encounter an unexpected obstacle.
    To encourage an understanding of the phenomenon of countersteering, the phrase positive steering is sometimes used,[18][19] and is summed up in a simplified way as "Push the right-hand bar to steer right; push the left-hand bar to steer left".

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