Side loads on wheels

Discussion in 'Cycling Equipment' started by James Annan, Jun 15, 2003.

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  1. James Annan

    James Annan Guest

    Something that I've been wondering about for some time, and I'd appreciate comments.

    Mostly, the loading on a wheel is in plane. However, when riding over rough ground and/or tight
    manouevring there sometimes seem to be significant side loads. Sometimes I can feel the wheel trying
    quite forcefully to turn under me and of course the ground force is quite close to the steering axis
    whereas my hands are a foot out to the sides on long handlebars. Probably some tacoed wheels can be
    atttributed to predominantly in-plane forces, but on the other hand these tacoes do not necessarily
    coincide with pinch flats.

    What I'm wondering is, what are the biggest side forces that are felt in MTBing, and a secondary
    question is what effect does this have on the spoke tension? I've seen some rough measurements
    posted here by Jim Papadopoulos (what happened to him) when he leant the bike to one side,
    indicating a substantial increase in tension on the lowest spokes on the under side as well as the
    large decrease in the ones on the higher side.

    James
     
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  2. Phil Holman

    Phil Holman Guest

    "James Annan" <[email protected]> wrote in message news:[email protected]...
    > Something that I've been wondering about for some time, and I'd appreciate comments.
    >
    > Mostly, the loading on a wheel is in plane. However, when riding over rough ground and/or tight
    > manouevring there sometimes seem to be significant side loads. Sometimes I can feel the wheel
    > trying quite forcefully to turn under me and of course the ground force is quite close to the
    > steering axis whereas my hands are a foot out to the
    sides
    > on long handlebars. Probably some tacoed wheels can be atttributed to predominantly in-plane
    > forces, but on the other hand these tacoes do
    not
    > necessarily coincide with pinch flats.
    >
    > What I'm wondering is, what are the biggest side forces that are felt
    in
    > MTBing, and a secondary question is what effect does this have on the spoke tension? I've seen
    > some rough measurements posted here by Jim Papadopoulos (what happened to him) when he leant the
    > bike to one
    side,
    > indicating a substantial increase in tension on the lowest spokes on
    the
    > under side as well as the large decrease in the ones on the higher
    side.

    With biking in general, most turns are coordinated or a crash will result. This usually means the
    resultant load of lateral tire traction and weight is always in plane with the wheel. Having said
    that, when traveling in a straight line it is possible to shift the bicycle to one side and
    compensate by shifting body weight to maintain balance. The resultant wheel load has to pass through
    the cg of the bicycle and rider combination to maintain balance. It is possible to exaggerate this
    to obtain a large side load but this is really an abuse load as it is not normal riding. Assuming a
    lean of ~30 deg from vertical, the lateral load on each wheel would be approximately half the in
    plane load.

    Phil Holman
     
  3. "James Annan" <[email protected]> wrote in message news:[email protected]...
    >However, when riding over rough ground and/or tight manouevring there sometimes seem to be
    >significant side loads.

    I have measured between the pad deflection in the "lab" (due to a load applied close to the actual
    RCP) and also while actually riding on the road. The results, with no real analysis can be seen at:

    http://tinyurl.com/7o9q

    Not quite so sure I buy into your "rough road" line of thinking - but anything out of the saddle
    will contribute to the loading that you describe.
    --
    ==================
    Kraig Willett www.biketechreview.com
    ==================
     
  4. Jobst Brandt

    Jobst Brandt Guest

    James Annan writes:

    > What I'm wondering is, what are the biggest side forces that are felt in MTBing, and a secondary
    > question is what effect does this have on the spoke tension? I've seen some rough measurements
    > posted here by Jim Papadopoulos (what happened to him) when he leaned the bike to one side,
    > indicating a substantial increase in tension on the lowest spokes on the under side as well as the
    > large decrease in the ones on the higher side.

    They aren't large because bicycle riding is a balanced act. Wheels are made with front hubs as
    wide as they are because when leaning the bicycle from the plumb line (when pedaling standing),
    the lean angle doesn't exceed that of the lateral spoke angle. You can test this by sighting down
    to the rim through the hub wile riding in this mode. That is about as far as side loads go in
    riding without falling.

    Jobst Brandt [email protected] Palo Alto CA
     
  5. James Annan

    James Annan Guest

    "Phil Holman" <[email protected]> wrote in message
    news:<[email protected]>...

    > With biking in general, most turns are coordinated or a crash will result. This usually means the
    > resultant load of lateral tire traction and weight is always in plane with the wheel. Having said
    > that, when traveling in a straight line it is possible to shift the bicycle to one side and
    > compensate by shifting body weight to maintain balance. The resultant wheel load has to pass
    > through the cg of the bicycle and rider combination to maintain balance. It is possible to
    > exaggerate this to obtain a large side load but this is really an abuse load as it is not normal
    > riding. Assuming a lean of ~30 deg from vertical, the lateral load on each wheel would be
    > approximately half the in plane load.

    While that is all true, it's not really relevant to what I was asking. Perhaps I could have been
    more clear. I'm talking about MTBing on bumpy and/or loose surfaces, where for example the wheels
    will often get knocked from one side or slip momentarily.

    James
     
  6. James Annan

    James Annan Guest

    [email protected] wrote in message news:<t%8Ha.2737$%[email protected]>...

    > They aren't large because bicycle riding is a balanced act. Wheels are made with front hubs as
    > wide as they are because when leaning the bicycle from the plumb line (when pedaling standing),
    > the lean angle doesn't exceed that of the lateral spoke angle. You can test this by sighting down
    > to the rim through the hub wile riding in this mode. That is about as far as side loads go in
    > riding without falling.

    Certainly in normal riding I've no problem in accepting this. However I've heard (perhaps somewhat
    apocryphal) stories of tandemers folding up the front wheel while climbing slowly up a steep hill or
    otherwise manouevring slowly (especially when the front wheel has a disk brake and is therefore
    dished and relatively weak). This probably has more to do with large steering excursions and/or
    riders lurching about rather than substantial leaning of the bicycle.

    Another way of approaching the question would be to ask: what sort of side loads will a wheel stand
    before it does fail? Obviously it will also depend on the simultaneous in-plane load. There's no
    question that MTB wheels do see some side loads, this may be better considered as a case of
    near-crashing rather than just riding along. I think it's fair to say that _some_ tacoed wheels are
    probably the cause of a crash, rather than its result. Ie the rider would have expected to stay
    upright but the wheel folded up.

    James
     
  7. Jobst Brandt

    Jobst Brandt Guest

    James Annan writes:

    >> With biking in general, most turns are coordinated or a crash will result. This usually means the
    >> resultant load of lateral tire traction and weight is always in plane with the wheel. Having said
    >> that, when traveling in a straight line it is possible to shift the bicycle to one side and
    >> compensate by shifting body weight to maintain balance. The resultant wheel load has to pass
    >> through the cg of the bicycle and rider combination to maintain balance. It is possible to
    >> exaggerate this to obtain a large side load but this is really an abuse load as it is not normal
    >> riding. Assuming a lean of ~30 deg from vertical, the lateral load on each wheel would be
    >> approximately half the in plane load.

    > While that is all true, it's not really relevant to what I was asking. Perhaps I could have been
    > more clear. I'm talking about MTBing on bumpy and/or loose surfaces, where for example the wheels
    > will often get knocked from one side or slip momentarily.

    That is the same as the case described. To cause significant side load on the wheel, requires
    sliding sideways into a solid stop, most likely crashing in the event. The lateral force on
    the wheel would be generated by rider leg mass that causes a side force between saddle and
    ground contact patch. The rider's mass on the saddle cannot develop a side load on the ground
    contact patch.

    Jobst Brandt [email protected] Palo Alto CA
     
  8. Jobst Brandt

    Jobst Brandt Guest

    James Annan writes:

    >> With biking in general, most turns are coordinated or a crash will result. This usually means the
    >> resultant load of lateral tire traction and weight is always in plane with the wheel. Having said
    >> that, when traveling in a straight line it is possible to shift the bicycle to one side and
    >> compensate by shifting body weight to maintain balance. The resultant wheel load has to pass
    >> through the cg of the bicycle and rider combination to maintain balance. It is possible to
    >> exaggerate this to obtain a large side load but this is really an abuse load as it is not normal
    >> riding. Assuming a lean of ~30 deg from vertical, the lateral load on each wheel would be
    >> approximately half the in plane load.

    > While that is all true, it's not really relevant to what I was asking. Perhaps I could have been
    > more clear. I'm talking about MTBing on bumpy and/or loose surfaces, where for example the wheels
    > will often get knocked from one side or slip momentarily.

    That is the same as the case described. To cause significant side load on the wheel, requires
    sliding sideways into a solid stop, most likely crashing in the event. The lateral force on the
    wheel would be generated by rider leg mass via the pedals that causes a side force between saddle
    and ground contact patch. The rider's mass on the saddle cannot develop a side load on the ground
    contact patch.

    Jobst Brandt [email protected] Palo Alto CA
     
  9. James Annan <[email protected]> wrote:

    > Another way of approaching the question would be to ask: what sort of side loads will a wheel
    > stand before it does fail? Obviously it will also depend on the simultaneous in-plane load.

    Forgetting the in-plane load for a moment (I know, it slackens the spokes, yadda yadda, but I doubt
    this matters with a well-built wheel), have you ever made a field repair to a potato-chipped wheel
    by whacking it on the ground? The amount of bashing a normal wheel will take (or needs, once
    potato-chipped, in order to be trueable) is pretty damn impressive.

    > There's no question that MTB wheels do see some side loads, this may be better considered as a
    > case of near-crashing rather than just riding along. I think it's fair to say that _some_ tacoed
    > wheels are probably the cause of a crash, rather than its result. Ie the rider would have expected
    > to stay upright but the wheel folded up.

    For me, this definitely falls in the category of things I am not going to worry about while mountain
    biking. I don't ride a tandem, but still find it hard to believe that even a tandem will do this
    without extreme measures.
     
  10. James Annan

    James Annan Guest

    [email protected] wrote:

    >
    > That is the same as the case described. To cause significant side load on the wheel, requires
    > sliding sideways into a solid stop, most likely crashing in the event. The lateral force on the
    > wheel would be generated by rider leg mass via the pedals that causes a side force between saddle
    > and ground contact patch. The rider's mass on the saddle cannot develop a side load on the ground
    > contact patch.

    The handlebars provide a handy lever for applying torques, and for that matter the pedals are
    (mumble) distance from the bike centerline.

    I think we are talking somewhat at cross purposes here. Your comments are (I think) basically
    considering a near-equilibrium situation, which is reasonable enough for most road riding (and most
    off-road riding too). But when just riding along, I can easily apply a large impusive downward force
    on one side of the handlebars, at will. This generates a sideways reaction force at the ground. The
    total impulse is limited, but I see no trivial upper limit on the momentary forces I can apply. Of
    course there is no particular reason for me to do this while just riding along on level ground, but
    when bumping over rough ground I can certainly feel the wheel being knocked from side to side in my
    hands (since the side forces are close to the steering axis, this suggests they could be quite
    large). I can also feel myself putting substantially more weight on one end of the bars and then the
    other, as I try to keep balanced. Maybe this is close to crashing, but I think it's also pretty
    normal for MTBing. It's not stuff that could be ridden no-hands.

    James
     
  11. James Annan wrote:
    >
    > [email protected] wrote:
    >
    > >
    > > That is the same as the case described. To cause significant side load on the wheel, requires
    > > sliding sideways into a solid stop

    Experimented with monostay forks once. The first versions were unridable at low speeds because of
    flex. To me that indicates that at low speeds significant sideforces are fed into the wheel to
    keep upright

    --
    Marten
     
  12. W K

    W K Guest

    <[email protected]umni.org> wrote in message news:BGcHa.2810$%[email protected]...

    > That is the same as the case described. To cause significant side load on the wheel, requires
    > sliding sideways into a solid stop, most likely crashing in the event. The lateral force on the
    > wheel would be generated by rider leg mass via the pedals that causes a side force between saddle
    > and ground contact patch. The rider's mass on the saddle cannot develop a side load on the ground
    > contact patch.

    Not disagreeing with that last sentence, but what if you stand up, and push the bike to one side as
    you keep going forward - doesn't that give a lateral force?

    Not that its usually sensible or useful to do such a thing, but I see kids on MTBs and BMXs doing it
    fairly often.
     
  13. Jobst Brandt

    Jobst Brandt Guest

    Benjamin Weiner writes:

    >> Another way of approaching the question would be to ask: what sort of side loads will a wheel
    >> stand before it does fail? Obviously it will also depend on the simultaneous in-plane load.

    > Forgetting the in-plane load for a moment (I know, it slackens the spokes, yadda yadda, but I
    > doubt this matters with a well-built wheel), have you ever made a field repair to a potato-chipped
    > wheel by whacking it on the ground? The amount of bashing a normal wheel will take (or needs, once
    > potato-chipped, in order to be trueable) is pretty damn impressive.

    Impressive! Yes, that is about all it is. Anything you can do with such violence can be done far
    better and with more control, statically. That is, a bent wheel should be laid on the ground, with
    the biggest wow toward the operator, pressing down on either side of that point with the hands or
    knees near the diameter. If the rim looks salvageable, do this only after loosening all spokes about
    a half turn to one turn, regardless of whether they are tight or loose. You can read about this in
    "the Bicycle Wheel" and how and why it works. I have done this on several occasions on the road, far
    from anywhere, for tourists who had a collapsed wheel.

    >> There's no question that MTB wheels do see some side loads, this may be better considered as a
    >> case of near-crashing rather than just riding along. I think it's fair to say that _some_ tacoed
    >> wheels are probably the cause of a crash, rather than its result. Ie the rider would have
    >> expected to stay upright but the wheel folded up.

    > For me, this definitely falls in the category of things I am not going to worry about while
    > mountain biking. I don't ride a tandem, but still find it hard to believe that even a tandem will
    > do this without extreme measures.

    An overloaded wheel (too few spokes, not enough tension) can easily collapse under trivial side
    loads, the kind common in bicycling. That is why tension and number of spokes is important. Most
    riders don't know how close they are to wheel collapse with low spoke count wheels, but that doesn't
    matter since most riders don't demand much from these wheels. That came to mind when hearing a
    four-strut Spinergy wheels go by with rattling 'spokes', the rider being sure they were safe. These
    wheels were initially tension spoked but lost that tension with age and were still widely used in
    that condition.

    http://home.interlynx.net/~pjdu/

    Jobst Brandt [email protected] Palo Alto CA
     
  14. Jobst Brandt

    Jobst Brandt Guest

    James Annan writes:

    >> That is the same as the case described. To cause significant side load on the wheel, requires
    >> sliding sideways into a solid stop, most likely crashing in the event. The lateral force on the
    >> wheel would be generated by rider leg mass via the pedals that causes a side force between saddle
    >> and ground contact patch. The rider's mass on the saddle cannot develop a side load on the ground
    >> contact patch.

    > The handlebars provide a handy lever for applying torques, and for that matter the pedals are
    > (mumble) distance from the bike centerline.

    I thin you should do some calculations on how much lateral force you can put on the wheel that way.
    Besides, it should be apparent that if there is a side load, it must cause lean in the plane of the
    bicycle. Pushing down on a pedal while pulling up on the bars is a closed loop and does not involve
    the wheels.

    > I think we are talking somewhat at cross purposes here. Your comments are (I think) basically
    > considering a near-equilibrium situation, which is reasonable enough for most road riding (and
    > most off-road riding too). But when just riding along, I can easily apply a large impulsive
    > downward force on one side of the handlebars, at will.

    I don't believe it. What do you call large force? Compare the lever length of a half bar and the
    distance to the road. Besides, as I said, this force is offset by the pedal force. If it weren't,
    you would fall off the bicycle.

    > This generates a sideways reaction force at the ground. The total impulse is limited, but I see no
    > trivial upper limit on the momentary forces I can apply. Of course there is no particular reason
    > for me to do this while just riding along on level ground, but when bumping over rough ground I
    > can certainly feel the wheel being knocked from side to side in my hands (since the side forces
    > are close to the steering axis, this suggests they could be quite large). I can also feel myself
    > putting substantially more weight on one end of the bars and then the other, as I try to keep
    > balanced. Maybe this is close to crashing, but I think it's also pretty normal for MTBing. It's
    > not stuff that could be ridden no-hands.

    Please review where these forces arise and how they are applied to the bicycle. The deformation of
    the bicycle is not in the wheels as you perceive it.

    Jobst Brandt [email protected] Palo Alto CA
     
  15. Jobst Brandt

    Jobst Brandt Guest

    W K Hyagillot writes:

    >> That is the same as the case described. To cause significant side load on the wheel, requires
    >> sliding sideways into a solid stop, most likely crashing in the event. The lateral force on the
    >> wheel would be generated by rider leg mass via the pedals that causes a side force between saddle
    >> and ground contact patch. The rider's mass on the saddle cannot develop a side load on the ground
    >> contact patch.

    > Not disagreeing with that last sentence, but what if you stand up, and push the bike to one side
    > as you keep going forward - doesn't that give a lateral force?

    Yes, and that has been mentioned here often. The amount of side load is shown by the lean angle of
    the bicycle and that angle stays within the lateral spoke angle. While standing you can sight
    through the front hub to the rim and note that the rim centerline does not go outside of the flanges
    unless you are specifically trying to do that.

    > Not that its usually sensible or useful to do such a thing, but I see kids on MTBs and BMXs doing
    > it fairly often.

    So what. I do that to test whether a wheel has any spoke twist by coasting along slowly and leaning
    as far as I can off center while standing on one pedal. The wheel withstands this easily.

    Jobst Brandt [email protected] Palo Alto CA
     
  16. Jobst Brandt wrote:

    >>>That is the same as the case described. To cause significant side load on the wheel, requires
    >>>sliding sideways into a solid stop

    Marten Gerritsen demurred:

    > Experimented with monostay forks once. The first versions were unridable at low speeds because of
    > flex. To me that indicates that at low speeds significant sideforces are fed into the wheel to
    > keep upright

    I don't think so. I'd imagine that the problem was lack of torsional rigidity in the fork blade,
    introducing hysterisis to the steering. This would be most noticeable at low speeds, where steering
    corrections are of larger magnitude.

    Sheldon "Bifurcated" Brown +-------------------------------------+
    | Natural laws have no pity. | --Robert A. Heinlein |
    +-------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
    617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
    http://captainbike.com http://sheldonbrown.com
     
  17. Sheldon Brown wrote:
    >
    > Jobst Brandt wrote:
    >
    > >>>That is the same as the case described. To cause significant side load on the wheel, requires
    > >>>sliding sideways into a solid stop
    >
    > Marten Gerritsen demurred:
    >
    > > Experimented with monostay forks once. The first versions were unridable at low speeds because
    > > of flex. To me that indicates that at low speeds significant sideforces are fed into the wheel
    > > to keep upright
    >
    > I don't think so. I'd imagine that the problem was lack of torsional rigidity in the fork blade,
    > introducing hysterisis to the steering. This would be most noticeable at low speeds, where
    > steering corrections are of larger magnitude.

    Don't believe it, and anyhow you can't feed very much torque through the contact patch. And it
    doesn't mesh with the feeling of the fronthub bending towards the pedals at turn in and popping back
    again once the turn starts

    Marten
     
  18. Tim McNamara

    Tim McNamara Guest

    In article <[email protected]>, M-Gineering import & framebouw
    <[email protected]> wrote:

    > Sheldon Brown wrote:
    > >
    > > Jobst Brandt wrote:
    > >
    > > >>>That is the same as the case described. To cause significant side load on the wheel, requires
    > > >>>sliding sideways into a solid stop
    > >
    > > Marten Gerritsen demurred:
    > >
    > > > Experimented with monostay forks once. The first versions were unridable at low speeds because
    > > > of flex. To me that indicates that at low speeds significant sideforces are fed into the wheel
    > > > to keep upright
    > >
    > > I don't think so. I'd imagine that the problem was lack of torsional rigidity in the fork blade,
    > > introducing hysterisis to the steering. This would be most noticeable at low speeds, where
    > > steering corrections are of larger magnitude.
    >
    > Don't believe it, and anyhow you can't feed very much torque through the contact patch. And it
    > doesn't mesh with the feeling of the fronthub bending towards the pedals at turn in and popping
    > back again once the turn starts

    Correct me if I'm wrong, but this would be the result of the monoblade fork failling to hold the hub
    perpendicular to the plane of steering. That's a very different situation than a standard fork which
    loads the hub basically equally on both side of the wheel. The problem you describe is with the fork
    being inadequate to the design task and would make a single track two wheel vehicle like a bicycle
    very difficult to ride.

    I would think that with all the load concentrated on one end of the axle, the wheel would be loaded
    quite differently than with a normal fork. A much larger diameter fork would seem necessary as would
    a larger diameter stub axle and a much less flexible attachment method than a bicycle-style dropout.
    After all, this becomes basically a 100 mm lever with bending forces acting in multiple directions
    from vertical load, braking loads and turning loads.

    Frankly I have never been able to see why anyone bothers with trying to make this design work. The
    benefits seem relatively few. Mike Burrows has been at it for years and hasn't been able to convince
    any manufacturer totake this on on a large scale commercial product. He used it on the Lotus bike,
    on the Windcheetah, the RatCatcher and his current cargo bike (front and rear, with the wheels not
    in the same line), and he tried with a plastic utility/shopper bike that he piched to Giant about 5
    years ago.
     
  19. James Annan

    James Annan Guest

    [email protected] wrote in message news:<94mHa.2942$%[email protected]>...
    > James Annan writes:
    >
    >
    > > The handlebars provide a handy lever for applying torques, and for that matter the pedals are
    > > (mumble) distance from the bike centerline.
    >
    > I thin you should do some calculations on how much lateral force you can put on the wheel
    > that way.

    If I push on the end of the handlebar towards the contact patch with an impulsive load of X, then
    the reaction at the ground is roughly X vertically and X/4 laterally (30cm half-width of bar, at
    1.2m height). If I pull up on the other bar at the same time, the angle of the net reaction force is
    even wider. Of course there is also a net reaction on the rider too, but the change in his momentum
    depends on the duration for which the force is applied, as well as its magnitude.

    > Besides, it should be apparent that if there is a side load, it must cause lean in the plane of
    > the bicycle. Pushing down on a pedal while pulling up on the bars is a closed loop and does not
    > involve the wheels.

    Again you seem to be talking about steady(ish) loads applied for some time. I'm talking about the
    impulsive forces which are certainly much greater, but are of course only applied very briefly.
    Bottoming out a suspension fork requires typically double the rider's weight on the fork alone, and
    pinch flats imply an even greater force. Rim dings and bent handlebars presumably require even
    greater forces since these events are rarer, but they still do happen. Surely these forces are
    _predominantly_ in the plane of the bicycle, but I see no justification for the assertion that the
    net effect of these forces necessarily lies within the spoke bracing angle. If you like, perhaps you
    can consider them to be a succession of sharp steering corrections where the bicycle is not leant in
    plane with the rider. This seems to me to be pretty much what happens on some bumpy descents.

    James
     
  20. Jobst Brandt

    Jobst Brandt Guest

    James Annan writes:

    >>> The handlebars provide a handy lever for applying torques, and for that matter the pedals are
    >>> (mumble) distance from the bike centerline.

    >> I thin you should do some calculations on how much lateral force you can put on the wheel
    >> that way.

    > If I push on the end of the handlebar towards the contact patch with an impulsive load of X, then
    > the reaction at the ground is roughly X vertically and X/4 laterally (30cm half-width of bar, at
    > 1.2m height). If I pull up on the other bar at the same time, the angle of the net reaction force
    > is even wider. Of course there is also a net reaction on the rider too, but the change in his
    > momentum depends on the duration for which the force is applied, as well as its magnitude.

    Hold it! Let's make a free body diagram and see where the loads arise. You cannot unilaterally push
    down on one bar-end unless you unload another area or lean off the bicycle to that side. I don't
    dispute that off center loads occur, only that they are not what you propose and are insignificant
    in magnitude.

    >> Besides, it should be apparent that if there is a side load, it must cause lean in the plane of
    >> the bicycle. Pushing down on a pedal while pulling up on the bars is a closed loop and does not
    >> involve the wheels.

    > Again you seem to be talking about steady(ish) loads applied for some time. I'm talking about the
    > impulsive forces which are certainly much greater, but are of course only applied very briefly.
    > Bottoming out a suspension fork requires typically double the rider's weight on the fork alone,
    > and pinch flats imply an even greater force. Rim dings and bent handlebars presumably require even
    > greater forces since these events are rarer, but they still do happen. Surely these forces are
    > _predominantly_ in the plane of the bicycle, but I see no justification for the assertion that the
    > net effect of these forces necessarily lies within the spoke bracing angle.

    I didn't say necessarily but only that they do so. That is why hubs are as wide as they are. This
    width takes care of the 99.9th percentile of occurrences.

    > If you like, perhaps you can consider them to be a succession of sharp steering corrections where
    > the bicycle is not leant in plane with the rider. This seems to me to be pretty much what happens
    > on some bumpy descents.

    No, not unless you are purposely trying to skid the wheel sideways. That is the way most non-crash
    wheel collapses are achieved. Skid on dirt, turn the wheel crosswise and hit an obstacle. It
    behooves the rough terrain rider to get good at not doing this. My MTB is my road bicycle is my
    touring bicycle and it goes everywhere. Collapsing wheels is not one of my worries and hasn't been
    over many years.

    Jobst Brandt [email protected] Palo Alto CA
     
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