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  1. #151
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    Here's a video of a Segway driving up and down a steep slope. Note the Segway is moving at a constant velocity and is not accelerating. However the rider can be seen to lean forwards markedly. Why does she need to do this and why does she not fall forward. Does it make sense that a faster rider or a shorter rider of the same weight would need to lean forwards even more?
    Steep segway climb - YouTube

    There is clearly some leverage involved in stopping the rider from falling forwards.. Could this leverage be categorized as the class three? And could the leverage result from the torque reaction to the motor/gearbox?
    I'm not so good at the numbers side of all this, I seem to 'see' more complex mechanics problems in my mind or feel it on the bike but struggle to work through the actual maths in detail. So I can't put the sums together here without a headache and a few hours, if at all, but I think yes, surely you lean forwards due to the torque reaction? Like countering a rearward thrust you feel under acceleration. Maybe I'm simplifying this due to not fully grasping the problem though.
    When climbing over 25-30% in a low gear, despite the force on the crank and your fwd COG, your gearing must be so low that you can wheelie out easily if you move weight back a little. The force into the crank is bodyweight times 'x' (x is your strength adding to your weight) but the gearing multiplies the torque more than your strength or body position range on the bike multiplies your weight? (--edit to clarify - I mean when it gets limitingly steep. At that point you either can't pedal as you're trying so hard to balance your weight, or can't prevent loop-out if you can pedal hard enough). Is that not a torque reaction in the same way as the segway, the segway just simplifies it?

    All I do know is that when I've 'sessioned' steep climbs with friends, what stops us is the front wheel lifting over a bump and upseting balance, looping out, or stalling against uneven ground.. or fitness eventually / rapidly! My weight is at that point, it'll always be somewhere between the axles depending on what the wheels are going over and technique and skill count for all (ie weight in right place at right time) and the variance in bikes much less. Having said that, I'm talking about fairly conventional bikes, from std 26",29" to a Jones at the most extreme example. There's plenty of times when a really high BB, short cranks and short wheelbase would help keep the power going, but that same set up wouldn't be so good in other situations.

    I guess what I'm thinking is that good technique is always needed and a bike can't do all things well. It has to be biased well toward a riding style, but always needs a lot of dynamic input - that input is the beauty of a bicycle as well as what complicates these physics questions! You can make it easier for that input to effect the bike but much depends on the rider.

    Velobike - try Goldtec in the Uk, maybe via Tazzy on STW. Oval rings at a lower cost than Rotor. Not the most durable ime so far, mainly due to uneven pressure on the teeth and burring at the larger raduis area, but not bad at all, I like them. Great on the SS.
    Last edited by james-o; 09-30-2012 at 03:46 AM.

  2. #152
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    Quote Originally Posted by meltingfeather View Post
    The dragster example has a couple of key differences: weight as a critical design driver being primary.
    The dragster example was not intended to illustrate how forces behave in a bicycle. Just an example of how torque reaction and third class levers are used on other machines.

  3. #153
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    Aren't we talking about a couple of inches here? It seems to be a moot point.
    No, YOU don't understand. You're making an ass of yourself for all of eternity.

  4. #154
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    Quote Originally Posted by wmac View Post
    Aren't we talking about a couple of inches here? It seems to be a moot point.
    Yes and no!
    When it comes to the ideal positioning of the riders Center of Gravity we are talking about only making marginal gains. Which is only in the, impress your friends with your skill territory. But if you compare the steepness of the slope the Segway is climbing, described as 45 degrees (100%) but looks more like 80%. We are in the region of twice the incline that you can ride on a mountain bike. So making a bike that could climb as well as a Segway, would be a big step forwards.

    Imagine being able to do this on a mountain bike:
    Segway Steep hill with wipeout - YouTube

    Notice that the crash at the end happens because the motors don't have enough torque to counter the forward lean.
    Last edited by GrahamWallace; 09-30-2012 at 05:20 AM.

  5. #155
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    Wow, I am surprised that Cloxxki and David Copperfield have not chimed in on this one.

    Your style of riding is far too regionalized. Those bikes would suck in the dez and just about everywhere were you need to make time between features on even terrain.

    If you so want recognition for inventing 29" wheels you should nominate Geoff to the MTBOF (mtnbikehalloffame.com), stuff the ballot box with your band of merrymen, and then bring a few bikes to Vegas for the induction next year.

    They nominated a cigarette smoking non bike riding guy this year by that method so you stand a chance of getting him in to the club but I would wager no chance on the trails. Not saying you couldn't ride them but you won't be able to hang.
    A bike by any other name is still a bike.

  6. #156
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    I am afraid that the style of voting for the MTBHOF is far too regionalized.

  7. #157
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    Quote Originally Posted by Bigwheel View Post
    ...Your style of riding is far too regionalized. Those bikes would suck in the dez and just about everywhere were you need to make time between features on even terrain.

    If you so want recognition for inventing 29" wheels you should nominate Geoff to the MTBOF (mtnbikehalloffame.com)....
    I very much doubt he needs to chase recognition. He already has that where it matters, except maybe in the small region called USA.

    As for the invention of big wheels, perhaps you could enlighten us as to who you believe had the first application of them to purpose built all terrain bicycles. (And the big wheeled fat tyred bikes of 100 years ago don't count because the geometry of those bikes was road oriented).
    As little bike as possible, as silent as possible.
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  8. #158
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    Segway video - it shows a guy leaning forward as he goes up the hill at constant speed. My understanding of the segway is that you signal it to move by leaning forward. Also, almost all the weight of the Segway is at the bottom, so the center of mass of the seqway plus rider is very low. He is leaning just barely forward, with center of mass still near the tire contact patch. The forward lean causes the Segway to tilt, but not enough to tip it forward. I don't thing there is any torque reaction involved in this.

    Leaning forward to me is similar to leaning forward on a skateboard. Going up hill, hitting a bump or decelleration causes a weight shift back, so you lean forward in anticipation of any deceleration.

    Conversely, when going downhill you lean back because a deceleration will cause a forward weight shift.

  9. #159
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    Dragster: I might be missing the whole concept of "torque reaction", but again I don't see it in this example.

    I don't think the front end of the dragster is long and weighted to counter a torque reaction. I think that front end lift comes from air lift and bumps in the road. In other words, on a perfectly smooth flat ideal track in a vacuum, the front end won't lift! (?)

    (The force of the engine is acting through the rear axle, which is higher than the front axle).
    Last edited by smilinsteve; 09-30-2012 at 12:11 PM.

  10. #160
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    Torque reaction - Torque reaction is the rotational equivalent of Newton's equal and opposite force reaction. Some good examples of this are a helicopter, where rotation of the blades tends to cause an opposite rotation of the helicopter body. Or a pneumatic nut driver, that causes a torque reaction that twists the tool in the operators hand.
    I don't see any torque reaction in the bike climbing a hill.

  11. #161
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    Quote Originally Posted by james-o View Post
    When climbing over 25-30% in a low gear, despite the force on the crank and your fwd COG, your gearing must be so low that you can wheelie out easily if you move weight back a little. The force into the crank is bodyweight times 'x' (x is your strength adding to your weight) but the gearing multiplies the torque more than your strength or body position range on the bike multiplies your weight? (--edit to clarify - I mean when it gets limitingly steep. At that point you either can't pedal as you're trying so hard to balance your weight, or can't prevent loop-out if you can pedal hard enough). Is that not a torque reaction in the same way as the segway, the segway just simplifies it?
    I still do not see any torque reaction coming into play in the bicycle hill climb. As the grade gets steeper, center of gravity moves back. The front wheel has less weight on it. That makes it more likely to lift if you pull on the handlebars, or hit a bump with the front tire.

  12. #162
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    Quote Originally Posted by smilinsteve View Post
    Segway video - it shows a guy leaning forward as he goes up the hill at constant speed. My understanding of the segway is that you signal it to move by leaning forward. Also, almost all the weight of the Segway is at the bottom, so the center of mass of the seqway plus rider is very low. He is leaning just barely forward, with center of mass still near the tire contact patch. The forward lean causes the Segway to tilt, but not enough to tip it forward. I don't thing there is any torque reaction involved in this.

    Leaning forward to me is similar to leaning forward on a skateboard. Going up hill, hitting a bump or decelleration causes a weight shift back, so you lean forward in anticipation of any deceleration.

    Conversely, when going downhill you lean back because a deceleration will cause a forward weight shift.
    Segway weight 83lbs

    Segway weight capacity: 260 pound (118 kg) rider and cargo.


    That would put the COG of rider and Segway around the top of the riders legs.

    HowStuffWorks "Segway: Car Replacement?"

  13. #163
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    Quote Originally Posted by smilinsteve View Post
    Dragster:
    I don't think the front end of the dragster is long and weighted to counter a torque reaction. I think that front end lift comes from air lift and bumps in the road. In other words, on a perfectly smooth flat ideal track in a vacuum, the front end won't lift! (?)
    Would then not the simple solution be to fit a short front end and suspension?

    Quote Originally Posted by smilinsteve View Post
    (The force of the engine is acting through the rear axle, which is higher than the front axle).
    The key distance is to have the COG at the same height as the rear axle as this would cancel out the tendency of the inertia focused at the COG to lift the front. But even then a mechanism is still required to cancel the torque reaction.

  14. #164
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    Quote Originally Posted by smilinsteve View Post
    Torque reaction - Torque reaction is the rotational equivalent of Newton's equal and opposite force reaction. Some good examples of this are a helicopter, where rotation of the blades tends to cause an opposite rotation of the helicopter body. Or a pneumatic nut driver, that causes a torque reaction that twists the tool in the operators hand.
    That's correct.

    Quote Originally Posted by smilinsteve View Post
    I don't see any torque reaction in the bike climbing a hill.
    Newton's Third Law: "To every action there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions".

    This also applies to rotational leverage forces known as torque, where a clockwise torque will always produce an "equal and opposite" anti-clockwise reaction.

    If the rear wheel has torque, there must be an equal and opposite force transmitted to the rest of the bike. However, the exact magnitude of this force will depend on the distance away from the axle that you measure it.
    Last edited by GrahamWallace; 09-30-2012 at 01:02 PM.

  15. #165
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    smilinsteve + Graham - is a torque reaction part of how we start a wheelie? Partly deliberate weight shift, partly using a low-ish gear to initiate that weight shift from the torque at the rear wheel. And popping wheelies is one thing that stops us climbing steep hills seated - mix of COG change due to the hill and the gearing producing more torque.
    And the dragster has a long wheelbase partly to help it steer straight, I thought. They have wheelie-bars to help against the torque reaction. I'm not sure why they don't have more downforce up front via aerofoils, probably since teh torque is highest when speed is lowest. But I'm a bit lost as to the original point of all this anyway )

    If you make a great hill-climber for 40% + grades you probably have a bike that won't ride well on other trails. I saw a bike with a 20" wheel once in an off-road hill-climb event .. kept the COG in the right place as well as good pedalling position - a rubbish all-round MTB though! The bush-whacking do-all in a trials-style ethic of a Cleland is great, but I think it'd need to do so without comproming flow at higher speeds too much to gain popularity. Niche appeal is no bad thing, but marginalisation is a shame.

    Velobike, I think those old roadsters aren't that far off the geometry of a Jones in some areas, and closer again to many really early MTBs? Exact numbers are different but the basis is similar, long rake forks, slack angles, long wheelbases and grips close to in-line with the steerer etc. I rode a early 1900s roadster once, very briefly, but it felt pretty good. I think people pointing out that no-one really 'invented' 700c off-road bikes have a valid point, they evolved slowly. To me, the early days of the Tour de France was the starting point of off-road riding - big mountains, dirt and mud roads, solo riders vs the terrain - the TDR isn't much different now. Culturaly it took the Marin Co downhillers to grab popular attention,and also for road riding to be something established that there could be an alternative to. Sometimes things have to settle in one area for some people to see a real difference in something new, or react against it and forge ahead in a different direction. But some rider/designers were pretty influencial between the 'birth of MTB' and now, and would have been more so if things like tyres that need a lot of £ to make hadn't influenced MTB direction. I'm just waffling now, no real point to make, just my thoughts on why these bikes and Geoff's ideas are recognised.

    I remember seeing a Highpath MTB in a magazine in the 80s and thinking the go-anywhere ideas in its design were exciting. No less so than the clunkers from Marin Co, just a different appeal.
    Last edited by james-o; 09-30-2012 at 01:19 PM. Reason: typos as ever..

  16. #166
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    Quote Originally Posted by james-o View Post
    And popping wheelies is one thing that stops us climbing steep hills seated - mix of COG change due to the hill and the gearing producing more torque.
    Yes, that's why it's pointless to fit a 15 tooth grannyring. The torque produced would either spin out the back wheel or tip you over backwards.

    Quote Originally Posted by james-o View Post
    I thought. They have wheelie-bars to help against the torque reaction. I'm not sure why they don't have more downforce up front via aerofoils, probably since teh torque is highest when speed is lowest.
    Long nose dragsters don't need wheelie-bars, as there is no need to have two mechanisms that do similar things. Modern dragsters do have aerofoils, though unlike torque reaction arms they only create downforce when the dragster is moving fast.

    Quote Originally Posted by james-o View Post
    But I'm a bit lost as to the original point of all this anyway )
    This all started when I suggested that moving the COG further away from the rear axle would reduce the torque reaction and so reduce front wheel lift.

    As moving the COG forwards would also reduce the weight on the rear wheel, it might to be more useful to move the COG upwards. And that this might explain why Clelands ridden out of the saddle climb so well.

  17. #167
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    Quote Originally Posted by james-o View Post
    ...If you make a great hill-climber for 40% + grades you probably have a bike that won't ride well on other trails...

    The bush-whacking do-all in a trials-style ethic of a Cleland is great, but I think it'd need to do so without comproming flow at higher speeds too much to gain popularity. Niche appeal is no bad thing, but marginalisation is a shame...
    I share that reservation, but I won't know for sure until I've tried a bike like that. Hill climbing is quite a specialised niche but there are quite a few people who really enjoy it. For example, I place a bike's climbing ability above its descending ability. Tests I have done to improve my lap times showed me that setting the bike up for climbing could save me 3 minutes in a lap, but only cost 1 minute on the descent (obviously that's very subjective and on one course, but it did work for me). The Cleland style bike is just as much a horse for its course as a downhill bike is for its. Maybe we need an uphill riding greasy hill championship



    Quote Originally Posted by james-o View Post
    ...Velobike, I think those old roadsters aren't that far off the geometry of a Jones in some areas, and closer again to many really early MTBs?...
    All the old roadsters I have ridden are great on the road, but truly horrible on technical terrain, but naturally I haven't ridden everything. The problem with the old roadsters mainly lies in the front fork rather than the frame geometry, so it's fixable.

    Here's some vintage pics of bikes with big wheels:

    A design for the future, P437 Cycling 1931

    [IMG]



    Racing and record breakers:


    Coolgardie 1896


    Francis Birtles, Warren & Robert Lennie, at Eucla WA, 1907. Lennies attempting Perth-Sydney record

    (The last 2 pictures are from the 1980 book,"The Bicycle and the Bush" by Jim Fitzpatrick, which is basically about the use of the bicycle in Australia from the 1880s to early 1900s)
    As little bike as possible, as silent as possible.
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  18. #168
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    Quote Originally Posted by GrahamWallace View Post
    Segway weight 83lbs

    Segway weight capacity: 260 pound (118 kg) rider and cargo.


    That would put the COG of rider and Segway around the top of the riders legs.

    HowStuffWorks "Segway: Car Replacement?"
    Ok and I think the top of the riders legs are pretty much over the tire contact patch.

  19. #169
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    Quote Originally Posted by Bigwheel View Post
    Wow, I am surprised that Cloxxki and David Copperfield have not chimed in on this one.

    .
    Yes it would be fun to hear from other physics nerds

  20. #170
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    Quote Originally Posted by GrahamWallace View Post
    Would then not the simple solution be to fit a short front end and suspension?
    Well, there have been short dragsters. I tried to find more info on the length of dragsters but admit I'm not really clear on the reason for the length, but I think it has to do with lateral stability. Since they don't have to corner, there is no limiting length in that respect. Shorter dragsters could have the same downward force on the front (more of the engine weight with less moment arm).



    The key distance is to have the COG at the same height as the rear axle as this would cancel out the tendency of the inertia focused at the COG to lift the front. But even then a mechanism is still required to cancel the torque reaction.
    You may be right about the force needing to be at the cog to avoid any moment, but if it was, then surely there would be no need to cancel a torque reaction since a force at the COG could cause no rotation at the COG?

  21. #171
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    Quote Originally Posted by Velobike View Post
    I very much doubt he needs to chase recognition. He already has that where it matters, except maybe in the small region called USA.

    Then why are you guys always coming here to toot you horn? If the us is such a small region then what does it matter what we think?

    As for the invention of big wheels, perhaps you could enlighten us as to who you believe had the first application of them to purpose built all terrain bicycles. (And the big wheeled fat tyred bikes of 100 years ago don't count because the geometry of those bikes was road oriented).
    To me there was not a true fat tire available for 700c rims until the advent of the "tire" in 1999. Until the you were doing your wandering about on 28" wheels which is not a bad thing, just not what developed in to the real thing.

    As I keep trying to point out mtb's are more than about plonking around in the glen. They are an efficient tool that should be able to handle a variety of terrain. Your bikes don't strike me as such but I am glad you all are having fun with them.
    A bike by any other name is still a bike.

  22. #172
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    Quote Originally Posted by GrahamWallace View Post
    That's correct.



    Newton's Third Law: "To every action there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions".

    This also applies to rotational leverage forces known as torque, where a clockwise torque will always produce an "equal and opposite" anti-clockwise reaction.

    If the rear wheel has torque, there must be an equal and opposite force transmitted to the rest of the bike. However, the exact magnitude of this force will depend on the distance away from the axle that you measure it.
    I don't get why you are splitting the force out of the torque or what the justification for doing so. Equal and opposite means the torque reaction is the same as the applied torque... whether it is made of a small force and a large arm or vice versa is inconsequential (unless you are building a dragster and the combination of short and heavier is a detriment to acceleration, among other things).
    Again, in your own example of COG at infinity the bike tips immediately upon input and you acknowledge this. How is that not a direct contradiction to your argument?
    It started for me when you said that raising COG equalizes weight distribution between the wheels, something I still dispute and which is very easily proven false.
    I don't think we're going to get anywhere, but it's been a pleasure.
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    Time to stop believing the hype and start doing some science.
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  23. #173
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    Quote Originally Posted by Bigwheel View Post
    To me there was not a true fat tire available for 700c rims until the advent of the "tire" in 1999. Until the you were doing your wandering about on 28" wheels which is not a bad thing, just not what developed in to the real thing.

    As I keep trying to point out mtb's are more than about plonking around in the glen. They are an efficient tool that should be able to handle a variety of terrain. Your bikes don't strike me as such but I am glad you all are having fun with them.
    I think I get what you're saying, if your mtb riding is centred around fast descents then you're right. I don't know about Graham but my riding is on all sorts of terrain, not just "plonking around the glen". Frequently I'll ride 20 or so miles just to get to the trail, come out somewhere on the other side of a mountain and then ride home. Often there will be stretches with no actual trail, just sheep pads or deer tracks, or a scramble over some scree carrying the bike.

    For your interest, the 28" wheels with a 2" tyre are the same size as a 29er with a 2.35", but most mountain riding in the UK prior to the mtb era was done on 27" rims, often fitted with 1*1/2" tyres. If you're interested in knowing more about traditional UK offroad riding, look at the the Rough Stuff Fellowship which has been going since 1955.
    As little bike as possible, as silent as possible.
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  24. #174
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    Graham,
    I'm starting to see some of what I had missed earlier. I think the term "torque reaction" was throwing me off, but if a force acts away from the center of gravity, it creates a moment.
    In my drawing, the front wheel is just starting to lift, so it has a normal force of zero. The rear tire contact patch is the fulcrum around which the COG is rotating.
    B is the vertical distance from the COg to the fulcrum and A is the horizontal distance to the fulcrum.
    F is the forward driving force from the tire/ground force, which we can say is acting at the COG.
    Mg is gravitation force acting on the center of mass, which I have broken into Mgx and Mgy (rather than throwing around sines and cosines )


    The sum of moments around the tire contact patch are zero at the time right before front tire lift, so
    M clockwise = M counterclockwise

    The clockwise moment is:

    Mgy (A)

    The counterclockwise moment is the sum of the moment caused by the drive force and that of gravity pulling the weight at the COG backward:

    Mgx (B) + F(B)

    The point of all this is to see what happens if you move the COG upward. distance A stays the same and distance B becomes greater at COG 2. So the counterclockwise moment becomes greater, and the wheel is more likely to lift.

    The only way to counter that lift from the higher COG is to also move it forward, so that the clockwise moment again balances the counterclockwise moment.
    Attached Thumbnails Attached Thumbnails Cleland: The original big wheeled off-road bicycle?-bicycle-free-body-diagram.jpg  

    Attached Files Attached Files

  25. #175
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    Quote Originally Posted by Bigwheel View Post
    To me there was not a true fat tire available for 700c rims until the advent of the "tire" in 1999. Until the you were doing your wandering about on 28" wheels which is not a bad thing, just not what developed in to the real thing.
    1999 WTB Nanoraptor dimensions: Otherwise known as "the tire"

    700x52c (marked size)
    A 700c rim diameter is 622mm add 52mm x 2 for the additional diameter of the tire to get an overall diameter of 726mm or 28.5826771653852 inches.

    So it appears that the worlds first 29er tire only measures 29inches when rounded up to the next integer.

    In Comparison:
    Nokia Hakkapeliitta snow tire dimensions
    (The tire used by Geoff Apps on his 1981 700c rimmed Cleland)

    700x47c (marked size)
    A 700c rim diameter is 622mm add 47mm x 2 for the additional diameter of the tire to get an overall diameter of 716mm or 28.188976377983202 inches.

    That makes the Nokia 10mm or 1.4% smaller in diameter

    A crucial difference?

    From the Cleland viewpoint it means 5mm more mud clearance.
    Last edited by GrahamWallace; 10-01-2012 at 10:21 AM. Reason: Typos

  26. #176
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    Great stuff. Thanks for that bit of history.
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    Quote Originally Posted by smilinsteve View Post
    Graham,
    I'm starting to see some of what I had missed earlier. I think the term "torque reaction" was throwing me off, but if a force acts away from the center of gravity, it creates a moment.
    Hi Steve, I like the drawing, it will definitely help to clarify the nature of the problem. I would have gone onto your technique of taking the sum of the moments acting on the CoG but thought is important to define the nature of torque reactions first. An alternate way of analysing the problem is by working out the sum of the vertical vector components and the horizontal vector components.

    The force that acts on the bike below the center of gravity does indeed create a moment but only when drive forces try to accelerate the CoG. These are what I call inertia forces/reaction forces but I believe that they are more commonly called weight transfer or load transfer forces.
    Weight transfer - Wikipedia, the free encyclopedia

    Weight transfer forces are similar but distinct from torque reaction forces in that they are only present in cases of acceleration or deceleration. Therefore, they do not apply to a Segway when it is climbing at a constant velocity. Torque reaction however, occurs whenever torque is present. For instance if you clamped the rear wheel of an electric bicycle to the floor and then started the motor in a low gear the front wheel would lift into the air even if the bicycle does not move forwards.



    Quote Originally Posted by smilinsteve View Post
    In my drawing, the front wheel is just starting to lift, so it has a normal force of zero. The rear tire contact patch is the fulcrum around which the COG is rotating.
    B is the vertical distance from the COg to the fulcrum and A is the horizontal distance to the fulcrum.
    F is the forward driving force from the tire/ground force, which we can say is acting at the COG.
    Mg is gravitation force acting on the center of mass, which I have broken into Mgx and Mgy (rather than throwing around sines and cosines )


    The sum of moments around the tire contact patch are zero at the time right before front tire lift, so
    M clockwise = M counterclockwise

    The clockwise moment is:

    Mgy (A)

    The counterclockwise moment is the sum of the moment caused by the drive force and that of gravity pulling the weight at the COG backward:

    Mgx (B) + F(B)

    The point of all this is to see what happens if you move the COG upward. distance A stays the same and distance B becomes greater at COG 2. So the counterclockwise moment becomes greater, and the wheel is more likely to lift.

    The only way to counter that lift from the higher COG is to also move it forward, so that the clockwise moment again balances the counterclockwise moment.

    One issue we need to agree on before we proceed, is the location of the fulcrum that the bike rotates around when the front wheel lifts off the ground. You have Identified it as the rear tire contact patch but may I suggest that it is in fact the rear axle. The reason being is that front lifts off the ground the rear tire does not rotate backwards but caries on moving forward. Wheel axles have a unique property in that unless they fall sideways they cannot be forced nearer to the ground. Also a tire surface rotating makes for a complicated form of fulcrum.

  28. #178
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    Quote Originally Posted by GrahamWallace View Post


    One issue we need to agree on before we proceed, is the location of the fulcrum that the bike rotates around when the front wheel lifts off the ground. You have Identified it as the rear tire contact patch but may I suggest that it is in fact the rear axle. The reason being is that front lifts off the ground the rear tire does not rotate backwards but caries on moving forward. Wheel axles have a unique property in that unless they fall sideways they cannot be forced nearer to the ground. Also a tire surface rotating makes for a complicated form of fulcrum.
    Yes I was pondering that very point. I have seen the analysis done both ways, and I'm not sure which is more correct. I can see the argument for using the rear axle rather than the tire contact patch as the fulcrum. Doing it this way, I don't think anything changes in the analysis I posted. Distance B becomes shorter (by the radius of the wheel), and distance A stays the same.

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    Quote Originally Posted by meltingfeather View Post
    I don't get why you are splitting the force out of the torque or what the justification for doing so. Equal and opposite means the torque reaction is the same as the applied torque...
    If the torque is say coming from a motor that is driving a wheel. And the casing of the motor is anchored to a lever, then the measurement of the torque reaction will depend on where along the lever you measure it. Only if you measure it at a point along the lever which is equal to the radius of the wheel will it be of the same magnitude.

    [QUOTE=meltingfeather;9737919
    Again, in your own example of COG at infinity the bike tips immediately upon input and you acknowledge this. How is that not a direct contradiction to your argument?
    [/QUOTE]
    I did indeed acknowledge that the inertia of the CoG at infinity would cause the bike to tip.
    (See Weight transfer - Wikipedia, the free encyclopedia for the reason why?)
    But in theory if the CoG was neither accelerating nor decelerating but traveling at a constant velocity there would be no force present to tip it. Of course traveling at a constant velocity on a bicycle up a steep hill is impossible, because of the pulsed nature of the drivetrain.


    [QUOTE=meltingfeather;9737919
    It started for me when you said that raising COG equalizes weight distribution between the wheels, something I still dispute and which is very easily proven false.
    I don't think we're going to get anywhere, but it's been a pleasure. [/QUOTE]

    For my part I am gaining insights and understanding that I would have not without having this discussion.

    Namely that what I refer to as CoG inertia more commonly known to motorsport enthusiasts as "axle weight-shift" is not the same phenomenon to torque reaction.

    On a bicycle weight shift is only caused by acceleration and deceleration.
    "So you can avoid the issues it creates by keeping your speed steady".

    Torque reaction is created whenever there is torque present in a system.
    It is unavoidable even in constant velocity situations.

    Therefore an electric powered mountain bike should be able to climb steeper slopes because of its smooth power delivery and ability to travel with constant velocity.
    Moving the center of mass upwards on such a machine would reduce the upwards leverage of the torque reaction trying to lift the front wheel, without raking any weight off the rear wheel.

    The next question is could a pedaled bicycle be made that had a torque delivery as smooth as an electric motor? Because if it could be made, such a bike should be able to climb slopes as steep as the Segway.

  30. #180
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    Quote Originally Posted by GrahamWallace View Post
    ...
    One issue we need to agree on before we proceed, is the location of the fulcrum that the bike rotates around when the front wheel lifts off the ground. You have Identified it as the rear tire contact patch but may I suggest that it is in fact the rear axle. The reason being is that front lifts off the ground the rear tire does not rotate backwards but caries on moving forward. Wheel axles have a unique property in that unless they fall sideways they cannot be forced nearer to the ground. Also a tire surface rotating makes for a complicated form of fulcrum.
    If I could butt in here with two questions...

    What happens when your COG falls in front of the rear axle, but behind the tyre contact patch?

    Assuming a constant pedaling speed, what happens to the forward velocity of the rear wheel once the bike starts rotating backwards?

    I believe that, in a simple model, the fulcrum is the tyre contact patch.
    Last edited by sbitw; 10-01-2012 at 11:34 PM. Reason: Clarification

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    Quote Originally Posted by GrahamWallace View Post
    If the torque is say coming from a motor that is driving a wheel. And the casing of the motor is anchored to a lever, then the measurement of the torque reaction will depend on where along the lever you measure it. Only if you measure it at a point along the lever which is equal to the radius of the wheel will it be of the same magnitude.
    I get more of what you're saying after thinking about it a bit more.
    However, you are saying "equal and opposite" and then turning around and saying the torque reaction depends on distance from the pivot. It does not. Equal and opposite is valid, the mechanism by which the force component of the torque reaction is reduced is the lengthening of the lever arm, which multiplies the force from a torque perspective. Since the mass stays the same in this case, I can see what you are talking about, but think the effect is negligible. You have been talking about torque reactions at constant velocity, which requires only enough torque to counter drag. Weight shift, especially on grade and with a pulsed drive, I think is much more of a driver, and raising the COG is detrimental in that case.
    Quote Originally Posted by GrahamWallace View Post
    For my part I am gaining insights and understanding that I would have not without having this discussion.
    Me too. I thought we had reached an impasse, which I didn't understand, since you seem to be a logical and educated fellow, so I gave it a bit more thought and I think I was looking past torque reactions to what I think is more of an effect.

    Quote Originally Posted by GrahamWallace View Post
    Namely that what I refer to as CoG inertia more commonly known to motorsport enthusiasts as "axle weight-shift" is not the same phenomenon to torque reaction.
    I get it now.

    Quote Originally Posted by GrahamWallace View Post
    On a bicycle weight shift is only caused by acceleration and deceleration.
    "So you can avoid the issues it creates by keeping your speed steady".
    It is also caused by grade. Changing the angle of incline of the bike has the same effect as summing the vertical weight vector with the horizontal one that results from acceleration on level ground.

    Quote Originally Posted by GrahamWallace View Post
    Torque reaction is created whenever there is torque present in a system.
    It is unavoidable even in constant velocity situations.
    I agree.

    Quote Originally Posted by GrahamWallace View Post
    Therefore an electric powered mountain bike should be able to climb steeper slopes because of its smooth power delivery and ability to travel with constant velocity.
    Moving the center of mass upwards on such a machine would reduce the upwards leverage of the torque reaction trying to lift the front wheel, without raking any weight off the rear wheel.
    This is impossible. The sum of the ground reactions at the two contact patches must equal the mass of the bike+rider.
    Like a weight distributing trailer hitch, the introduction of the moment causes a skew in the distribution, but not a difference in the sum of the ground reactions.
    Quote Originally Posted by GrahamWallace View Post
    The next question is could a pedaled bicycle be made that had a torque delivery as smooth as an electric motor? Because if it could be made, such a bike should be able to climb slopes as steep as the Segway.
    Sure... pedal it with a robot.
    Last edited by meltingfeather; 10-01-2012 at 10:00 PM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  32. #182
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    Wow the numbers and calculations in this thread are too much. You can spin it any way you want but the modern 700c Mt. Bike was based on the advent of the "tire". It created a market for high volume, low pressure tires that has gained an enormous following, won World Cups and Olympic Gold Medals as well as use on thousands of bikes that just plain old people ride in all sorts of ways and places all over the world. Not just some boggy glen in the British Isles.

    Here is a photo of a bike with Hakkapaleta's on it:

    Cleland: The original big wheeled off-road bicycle?-image.jpg


    While it may be close to the same height it lacks the volume and that folks is what made me subscribe back in 99'.

    For some reason my iPad won't allow me to post multiple pics as I was going to insert one of a "tire" for reference but just go look at what you have on your bike. Not a huge difference but big enough to make a difference.

    I would venture to say that the new Knard tire is an equal step above and I can't wait to give them a go. Life is incremental and that is what keeps it interesting. Innovation is key, not mucking about trying to figure out which came first, the chicken or the egg.
    A bike by any other name is still a bike.

  33. #183
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    Cleland: The original big wheeled off-road bicycle?-image.jpg
    A bike by any other name is still a bike.

  34. #184
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    Quote Originally Posted by sbitw View Post
    If I could butt in here with two questions...

    What happens when your COG falls in front of the rear axle, but behind the tyre contact patch?
    Hi sbitw,

    That's an interesting question. In my logic it depends where you believe the fulcrum is. If it is the axle then the CoG is still creating a small downwards moment of rotation even though it is directly above the contact point. If the contact point is the fulcrum then there will be no moment of rotation so the front wheel must lift. This will happen even when the bike is moving forward at a constant speed and there is no forces pushing the CoG backwards as the torque reaction alone will lift the front wheel. The front wheel accelerates as it lifts, the energy required for this is stolen from the torque of the rear wheel. But not enough energy will be required to stop the rear wheel from rotating forwards. If pedaling continues then the bike will continue to accelerate in its rotation around the axle but with gravity now assisting the back flip where earlier on it was resisting it.

    For the rear contact patch to be acting as the fulcrum the wheel would have to rotate backwards whilst its brake was applied.

    Quote Originally Posted by sbitw View Post
    Assuming a constant pedaling speed, what happens to the forward velocity of the rear wheel once the bike starts rotating backwards?
    The torque of the rear will be split between moving the bike forward and lifting the front end so the rear wheel must lose some forwards velocity.

    Quote Originally Posted by sbitw View Post
    I believe that, in a simple model, the fulcrum is the tyre contact patch.
    There may be an error in my reasoning,
    If there is, I am hoping that someone will spot it and point it out.

  35. #185
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    Quote Originally Posted by Bigwheel View Post
    Click image for larger version. 

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    Tucson Mountain Park?

  36. #186
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    Quote Originally Posted by GrahamWallace View Post
    1999 WTB Nanoraptor dimensions: Otherwise known as "the tire"

    700x52c (marked size)
    A 700c rim diameter is 622mm add 52mm x 2 for the additional diameter of the tire to get an overall diameter of 726mm or 28.5826771653852 inches.

    So it appears that the worlds first 29er tire only measures 29inches when rounded up to the next integer.

    In Comparison:
    Nokia Hakkapeliitta snow tire dimensions
    (The tire used by Geoff Apps on his 1981 700c rimmed Cleland)

    700x47c (marked size)
    A 700c rim diameter is 622mm add 47mm x 2 for the additional diameter of the tire to get an overall diameter of 716mm or 28.188976377983202 inches.

    That makes the Nokia 10mm or 1.4% smaller in diameter

    A crucial difference?

    From the Cleland viewpoint it means 5mm more mud clearance.

    Quote Originally Posted by Bigwheel View Post
    WYou can spin it any way you want but the modern 700c Mt. Bike was based on the advent of the "tire". It created a market for high volume, low pressure tires that has gained an enormous following, won World Cups and Olympic Gold Medals as well as use on thousands of bikes that just plain old people ride in all sorts of ways and places all over the world. Not just some boggy glen in the British Isles.
    But there were a string of events that led to the "tire",
    Cleland: The original big wheeled off-road bicycle?-hakkapeliitta014.jpg

    Quote Originally Posted by Bigwheel View Post
    While it may be close to the same height it lacks the volume and that folks is what made me subscribe back in 99'.
    I agree.

    Quote Originally Posted by Bigwheel View Post
    For some reason my iPad won't allow me to post multiple pics as I was going to insert one of a "tire" for reference but just go look at what you have on your bike. Not a huge difference but big enough to make a difference.
    The picture you show is not a 700x47c Nokia Hakkaoeliitta. Here is picture of one like those Geoff Apps exported to the US in the 1980's:
    Cleland: The original big wheeled off-road bicycle?-1981-cleland-aventura-700c-x-47-hakkapelliita-tires-finland.jpg
    And Here is a picture of a 1988 Bruce Gordon 700c "Rock N Road" tire. The tire that inspired Wes Williams, who with Garry Fisher commissioned the Nano-raptor. Notice that the tread pattern was copied from the Hakkapeliitta.
    Cleland: The original big wheeled off-road bicycle?-1988-bruce-gordon-rock-n-road-tire.jpg

  37. #187
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    Quote Originally Posted by GrahamWallace View Post
    The force that acts on the bike below the center of gravity does indeed create a moment but only when drive forces try to accelerate the CoG. These are what I call inertia forces/reaction forces but I believe that they are more commonly called weight transfer or load transfer forces.
    Weight transfer - Wikipedia, the free encyclopedia
    I think the torque reaction you keep talking about is the moment caused by the force pushing the bike forward. At constant velocity, this force is balanced with gravity and friction holding it back. Balanced forces, no net moment. When accelerating this force is larger than the counteracting forces. This creates a total moment about the COG. I don't think there is any other torque.

    Weight transfer forces are similar but distinct from torque reaction forces in that they are only present in cases of acceleration or deceleration. Therefore, they do not apply to a Segway when it is climbing at a constant velocity. Torque reaction however, occurs whenever torque is present. For instance if you clamped the rear wheel of an electric bicycle to the floor and then started the motor in a low gear the front wheel would lift into the air even if the bicycle does not move forwards.
    I can't picture the configuration of your electric bike, but if I clamp the rear wheel of a regular bike and step on the crank, the front end will not rise.

    Why does the bike have to be electric, and how does that change things? If an electric motor shaft is attached directly to the bottom bracket spindle, motor torque is converted to chain tension. Chain tension is converted to force on the rear cog. Since the wheel is clamped, there is no motion. No torque can be transmitted from the wheel to frame because the wheel is attached to the frame only by the axle with ball bearings. Only linear force can transfer from wheel to frame. You can't transfer a torque through a pivot point.

    When I went to school, the free body diagram would identify all forces and moments in the system. This torque reaction you are talking about seems to be something not identified in the drawing I made? Then where does it come from, where is it applied, and where is the force that generates it?
    Last edited by smilinsteve; 10-02-2012 at 12:38 PM.

  38. #188
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    Quote Originally Posted by Originally Posted by GrahamWallace
    Torque reaction is created whenever there is torque present in a system.
    It is unavoidable even in constant velocity situations.
    Quote Originally Posted by Meltingfeather
    I agree.

    I disagree. Is this the heart of the matter here?

    Newtons third law does not state that every torque creates an equal and opposite torque.

    Torque is just a force that creates rotational motion. That force could have a reaction that creates no rotational motion.

    Example:

    Force from your leg > torque at bottom bracket > Tension on chain > torque at wheel hub > force from tire on ground > equal and opposite reaction is linear force on wheel axle pushing bike forward.

    See how forces convert to torques which convert back to linear force?
    Forces have reactions. Forces can cause torque, or not. Torque can be converted to linear force with no equal and opposite torque.

    Example 2:

    Take your bike as above. Pin one end of the chain to your chainring. The other end of the chain is not attached to your wheel, but to the center of a wooden box sitting on the road.
    Push down on the crank;

    Force from leg > torque on bottom bracket > tension in chain > Linear motion of box.

    Example 3

    Same as example 2 but chain is attached to the top of a tall skinny box with high coefficient of friction between the box and the ground;

    Force from leg > torque on BB > tension on chain > torque on box, causing it to fall over.

    The difference between example 2 and 3 is whether or not the force from the chain acts through the COG. In example 3 it doesn't, and creates a torque.


    I guess what I'm getting at here Graham, is that if there is a "torque reaction" at the center of gravity of the rider, then it is caused by some force acting a distance away from the COG.

    I see the torque from pedaling creating a ground force below the COG that creates a moment about it.
    You seem to think there is another source for torque around the COG, but I don't see it.

  39. #189
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    Quote Originally Posted by smilinsteve View Post
    I think the torque reaction you keep talking about is the moment caused by the force pushing the bike forward. At constant velocity, this force is balanced with gravity and friction holding it back. Balanced forces, no net moment. When accelerating this force is larger than the counteracting forces. This creates a total moment about the COG. I don't think there is any other torque.

    Anything that rotates clockwise will create an anti-clockwise reaction. If you sit in a revolving chair, hold your arms outwards and then move them quickly clockwise, your body and the chair will rotate anti-clockwise as a reaction to the torque generated by the moving arms. Likewise if a bicycle wheel rotates clockwise there will be an anti-clockwise reaction in the frame.

    Quote Originally Posted by smilinsteve View Post
    I can't picture the configuration of your electric bike, but if I clamp the rear wheel of a regular bike and step on the crank, the front end will not rise.
    It may if you put it in a low gear, and definitely would if you placed the bike on a steep incline.

    Quote Originally Posted by smilinsteve View Post
    Why does the bike have to be electric, and how does that change things? If an electric motor shaft is attached directly to the bottom bracket spindle, motor torque is converted to chain tension. Chain tension is converted to force on the rear cog. Since the wheel is clamped, there is no motion. No torque can be transmitted from the wheel to frame because the wheel is attached to the frame only by the axle with ball bearings. Only linear force can transfer from wheel to frame. You can't transfer a torque through a pivot point.
    There is also an axle and ball bearing connection between a revolving chair and its base but it can still be made to rotate without you touching anything around you.

    Quote Originally Posted by smilinsteve View Post
    When I went to school, the free body diagram would identify all forces and moments in the system. This torque reaction you are talking about seems to be something not identified in the drawing I made? Then where does it come from, where is it applied, and where is the force that generates it?
    1/ It comes from the rear wheel torque.
    2/ It is applied to anything that stops it from moving freely.
    3/ My legs and feet and then the mechanical advantage is increased via low gearing.

  40. #190
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    Quote Originally Posted by smilinsteve View Post
    I disagree. Is this the heart of the matter here?
    I'm not sure.
    Quote Originally Posted by smilinsteve View Post
    Newtons third law does not state that every torque creates an equal and opposite torque.
    But they do. This is the basis for the sum of moments analytical tool in statics.

    Quote Originally Posted by smilinsteve View Post
    Torque is just a force that creates rotational motion. That force could have a reaction that creates no rotational motion.
    I do not believe it can.

    Quote Originally Posted by smilinsteve View Post
    Example:

    Force from your leg > torque at bottom bracket > Tension on chain > torque at wheel hub > force from tire on ground > equal and opposite reaction is linear force on wheel axle pushing bike forward.

    See how forces convert to torques which convert back to linear force?
    Forces have reactions. Forces can cause torque, or not. Torque can be converted to linear force with no equal and opposite torque.
    You took one force and translated it through at least four different bodies to arrive at your conclusion, which I'd say is a little larger in scope than what Newton intended.
    The reactions are between the individual bodies, not translated through a machine. The equal and opposite force from tire on ground is ground on tire. Likewise for every piece in your example.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  41. #191
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    I will try and explain torque reaction a different way.

    If you constrain a large force it will try and find anyway it can to break free.

    If you constrain the torque force in a rear wheel by giving it a large amount of resistance from the ground, then it will look for other places to escape. It could break the chain for instance, or it could cause the front wheel to lift off the ground. And the bicycle doesn't even need to move for this to happen.

    Newtons third Law refers to forces. All forces.

    They can be restrained and not visible like the tension in a chain.
    The same is true for reaction forces. But sometimes they find ways to unexpectedly break free.

    If torque reaction does not exist why invent "Torque Reaction Arms" ?
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    BMF Torque Wrench Co. - Model SD Wrenches
    Last edited by GrahamWallace; 10-02-2012 at 01:36 PM. Reason: Typos & add picture

  42. #192
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    Quote Originally Posted by meltingfeather
    You took one force and translated it through at least four different bodies to arrive at your conclusion, which I'd say is a little larger in scope than what Newton intended.
    The reactions are between the individual bodies, not translated through a machine. The equal and opposite force from tire on ground is ground on tire. Likewise for every piece in your example.
    Well, I'm thinking the action reaction pairs newton talked about are forces. Forces can create torque or not. So in my example, how would you break down the action reaction pairs?

    Force on pedal creates an opposite force from pedal to foot!
    In this case, it doesn't matter if that force from foot to pedal creates a torque or doesn't, but it does.

    In my example of the chain attached to the top of the box, the reaction to the force on the box by the chain is the force on the chain by the box. the chain creates a moment that topples the box, but what is the "torque reaction?" there doesn't need to be an equal and opposite torque, only an equal and opposite force.

  43. #193
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    Originally Posted by smilinsteve
    Newtons third law does not state that every torque creates an equal and opposite torque.
    Quote Originally Posted by meltingfeather
    But they do. This is the basis for the sum of moments analytical tool in statics.
    In statics, if a body isn't rotating, you know there is no net moment on it.

    But what does that have to do with bodys that are rotating? If I am in outer space and push on one end of an asteroid floting freely, the equal and opposite reaction to my push on the asteroid is a force against my hand. So I move backwards, and the asteroid starts rotating. So my push created a torque, but the equal and opposite reaction was a linear force against me causing me to move, not rotate.

  44. #194
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    This is going to be my last post to you Graham but let me say this. Stick to the things you know about what led Geoff to using 700c "off trail" and don't pretend to know what led Wes to his part in the "tire" or Gary Fisher either because you obviously don't.

    And btw, that pic of the tacoed wheel in your reply to my last post was probably not the best way to illustrate your point.
    A bike by any other name is still a bike.

  45. #195
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    Quote Originally Posted by smilinsteve View Post
    In statics, if a body isn't rotating, you know there is no net moment on it.

    But what does that have to do with bodys that are rotating? If I am in outer space and push on one end of an asteroid floting freely, the equal and opposite reaction to my push on the asteroid is a force against my hand. So I move backwards, and the asteroid starts rotating. So my push created a torque, but the equal and opposite reaction was a linear force against me causing me to move, not rotate.
    You could also push the asteroid in away that makes you rotate.It depends on where in your body the push originates relative to your center of mass.

  46. #196
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    There is also an axle and ball bearing connection between a revolving chair and its base but it can still be made to rotate without you touching anything around you
    In your swivel chair example the chair is analagous to the wheel and the base of the chair is analagous to the frame. You can spin that chair all you want, but you aren't going to transmit any torque to the base.

    It may if you put it in a low gear, and definitely would if you placed the bike on a steep incline.
    Your bike with the clamped wheel is an easy experiment to do at home, so lets do that and see what happens. I am sure you can not lift the front end of the bike. Draw a free body diagram and show the force that lifts the bike. ?
    If the rear wheel is clamped, say by a rear disc brake, the force on the crank creates internal forces in the frame transmitted from crank to chain to axle, and from brake rotor to caliper to frame, etc. There is no force between the bike and ground.
    Internal forces can not cause motion. Its like trying to grab the arms of your chair and lifting yourself off the ground while you are sitting it

  47. #197
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    If torque reaction does not exist why invent "Torque Reaction Arms" ?
    I already mentioned nut drivers as one example of a torque reaction. I don't see the analogy to a rider pedaling uphill.

    Again, a free body diagram, like I posted, is the way you analyse the forces and moments in a system.
    The way to do this problem is to evaluate the moments at the point of tire lift. I already showed the effect of moving the COG upward.

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    Quote Originally Posted by Bigwheel View Post
    This is going to be my last post to you Graham but let me say this. Stick to the things you know about what led Geoff to using 700c "off trail" and don't pretend to know what led Wes to his part in the "tire" or Gary Fisher either because you obviously don't.
    But I would like to know where I have gone wrong?

    Quote Originally Posted by Bigwheel View Post
    And btw, that pic of the tacoed wheel in your reply to my last post was probably not the best way to illustrate your point.
    Is a prototype that is 30years before its time not allowed a few teething troubles?

    Here is an independent view of 29er history:
    Guitar Ted Productions: The Beginnings Of The Modern 29"er: A History
    Last edited by GrahamWallace; 10-02-2012 at 03:58 PM. Reason: To add a link

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    Quote Originally Posted by GrahamWallace View Post
    You could also push the asteroid in away that makes you rotate.It depends on where in your body the push originates relative to your center of mass.
    Agreed, but I am trying to disprove what you said, that any system with a torque must have a torque reaction.

  50. #200
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    Quote Originally Posted by smilinsteve View Post
    Agreed, but I am trying to disprove what you said, that any system with a torque must have a torque reaction.
    And you have, and are right in pointing out that a force can be turned into a torque and a torque into a force.

    Now you need to find a stationary swivel chair, lift your feet off the floor, introduce some torque by waving your arms and legs and see if the chair rotates.

    Or failing that explain why a hovering helicopter needs a tail rotor?

    Or failing that research the difference between a torque reaction arm and a nut driver.

    Or drill a hole in a wall and see if the electric drill tries to rotate the opposite way to the bit.

    If Newton had meant that only a linear force has an equal and opposite reaction. Would not he have said so?

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