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  1. #201
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    Quote Originally Posted by GrahamWallace View Post
    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?
    Other than the chair, the examples are all related to shaft torque and when I google torque reaction, most hits also refer to shafts. These are obvious examples of torque reaction.
    For the bike riding up the hill, you need to draw a FBD with all forces and calculate all moments. I still think that my FBD shows all forces and moments.

    If you turn your bike upside down and turn the cranks, the cranks turn the wheel. The force of your arm applies a torque to the hub of the wheel causing it to accelerate.
    What other forces are acting on the bike?

    As for the chair, I am flapping away furiously, and not getting much movement, but want to think a bit more about this one, and hopefully no one will walk into my office.

  2. #202
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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 would also rotate, unless you just happened to push with a force that intersected your COG.
    Newton's 3rd law stops at the equal and opposite reactions... what happens to each body after that is 2nd law stuff (F=ma, or in the case of rotation, τ=Iα)
    Quote Originally Posted by pvd
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  3. #203
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    Quote Originally Posted by smilinsteve View Post
    For the bike riding up the hill, you need to draw a FBD with all forces and calculate all moments. I still think that my FBD shows all forces and moments.
    I think the drive force needs to be shown at the contact patch. It does not act at the COG, and that may be the issue.
    Quote Originally Posted by smilinsteve View Post
    If you turn your bike upside down and turn the cranks, the cranks turn the wheel. The force of your arm applies a torque to the hub of the wheel causing it to accelerate.
    What other forces are acting on the bike?
    The inertia of the wheel pushes back against the torque of the driving force.
    Quote Originally Posted by smilinsteve View Post
    As for the chair, I am flapping away furiously, and not getting much movement, but want to think a bit more about this one, and hopefully no one will walk into my office.
    You will only get small, local rotation, because in that case, the only "outside" force acting is the friction in the bearings/rotating mechanism of the chair, which is small. Without outside force there can be no net movement. Do "The Twist" and your chair should move back and forth opposite your torso.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  4. #204
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    Quote Originally Posted by smilinsteve View Post
    ...As for the chair, I am flapping away furiously, and not getting much movement, but want to think a bit more about this one, and hopefully no one will walk into my office.
    Just think, if only Newton had an electric drill, all this would have been worked out ages ago...

    Bigwheel, I don't know why you seem so upset about the claim to be first with the large wheel offroad bike. It doesn't take anything away from the guys who popularised/commercialised it or indeed from the USA mtb industry without whom we wouldn't have the modern mtb.

    The likes of the British bike industry studiously ignored the fact that there were people who spent their time riding offroad, and instead of leading the way continued to produce nothing but roadbikes. The demand had existed since the dawn of the bicycle age, and they constantly remained blind to it.

    I have a collection of bike books and magazines starting from the 1870s, and one constant in them is articles on pass-storming as it was called then. So the demand was there for suitable tyres and frames, which is possibly a chicken and egg thing.

    And without the Hakka, there would have been no big wheel mtb, so we should also be thanking the Finns.
    As little bike as possible, as silent as possible.
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  5. #205
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    Quote Originally Posted by smilinsteve View Post
    Other than the chair, the examples are all related to shaft torque and when I google torque reaction, most hits also refer to shafts. These are obvious examples of torque reaction.

    Could shaft be the same as = Axle?


    Quote Originally Posted by smilinsteve View Post
    I still think that my FBD shows all forces and moments.
    The big omission is the rear wheel's coefficient of friction with the ground. If the rear wheel can't slip the CoG can move right to the front of the wheel-base without any problem.

    For a FBD It would probably be a good idea to place the CoG directly above the center of the wheelbase so that the weight is split between the wheels.

    Quote Originally Posted by smilinsteve View Post
    For the bike riding up the hill, you need to draw a FBD with all forces and calculate all moments. I still think that my FBD shows all forces and moments.
    The more I think of this the more I think it may be possible. It would take some work and there would be two versions. One for an accelerating CoG. And one for a constant velocity CoG. (Someone mentioned earlier that a CoG rising up an incline whilst being pulled backwards by gravity is accelerating? Surely not as this just requires the motive vector to be stronger than the rearward pull of Gravity.

    Quote Originally Posted by smilinsteve View Post
    If you turn your bike upside down and turn the cranks, the cranks turn the wheel. The force of your arm applies a torque to the hub of the wheel causing it to accelerate.
    What other forces are acting on the bike?
    There is a small torque reaction force created by the rotational inertia of the mass off the rotating wheel though this is much larger during acceleration and deceleration. for a big torque reaction the wheel needs to be experiencing drag. In the case of a helicopter the drag comes the air resistance of the rotor blades.

    Quote Originally Posted by smilinsteve View Post
    As for the chair, I am flapping away furiously, and not getting much movement, but want to think a bit more about this one, and hopefully no one will walk into my office.
    Well I'am sitting here in my swivel chair spinning happily. Good job I am not at work!
    Physics Swivel Chair Olympics vol 7 - YouTube

    If you take a top view helicopter with its rotors rotating clockwise and its tail rotor to the right. Is this not similar to a bicycle when viewed from the side with the rear wheel representing the main rotors, the tail representing the top tube and the rotor now pushing downwards? The main difference being that in the bicycle it is rear wheel drag not air resistance causing a torque reaction. And that the down force of the tail rotor is replaced by the weight of the CoG in the bike?
    Last edited by GrahamWallace; 10-02-2012 at 03:56 PM. Reason: clarification

  6. #206
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    Pretty long thread for just five guys talking to eachother. Interesting topic though. Love the Fox hunting outfits you British guys wear!

  7. #207
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    Quote Originally Posted by ghettocop View Post
    Pretty long thread for just five guys talking to eachother. Interesting topic though.
    If we can get past the question of does torque reaction exist? And is it relevant issue? It may get even more Interesting

    Quote Originally Posted by ghettocop View Post
    Love the Fox hunting outfits you British guys wear!
    Thanks! The real reason that our bikes have high handlebars is so we can hold our umbrellas when we ride in the rain Though they also make a good rest for the shotgun.
    Last edited by GrahamWallace; 10-03-2012 at 02:21 PM. Reason: Bad punctuation

  8. #208
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    Yes a long line of people who contributed. Some credited for their input, some not., And some claiming they got the whole Idea just by looking at the size of the rocks on the Pearl Pass.

  9. #209
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    Quote Originally Posted by GrahamWallace View Post
    The more I think of this the more I think it may be possible. It would take some work and there would be two versions. One for an accelerating CoG. And one for a constant velocity CoG.
    One version is fine. It is either a statics problem (forces and moments balance), or a dynamics problem (forces and moments are partially balanced by masses accelerating).

    Quote Originally Posted by GrahamWallace View Post
    (Someone mentioned earlier that a CoG rising up an incline whilst being pulled backwards by gravity is accelerating? Surely not as this just requires the motive vector to be stronger than the rearward pull of Gravity.
    I don't think this is referencing a comment I made, because I did not say this, but just to be sure, because I did make a statement about "net effect" of an incline, what I said was that the incline, which results in the weight vector of the COG pointing partially rearward (toward the pivot), has the same net effect on the force balance as combining a vertical weight vector with a horizontal force vector accelerating the mass-- a rearward-pointing vector at the COG, which will tip the bike, given the proper geometry and magnitudes.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  10. #210
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    Quote Originally Posted by meltingfeather View Post
    you would also rotate, unless you just happened to push with a force that intersected your COG.
    Newton's 3rd law stops at the equal and opposite reactions... what happens to each body after that is 2nd law stuff (F=ma, or in the case of rotation, τ=Iα)
    Yes! That's pretty much what I was getting at. A force creates a reaction that may or may not create a moment. If it acts through the COG, then there is no moment. Any moments in the bicycle free body diagram are caused by forces acting away from the COG. If there is any torque reaction to be considered, then the force and the point of application needs to be identified.

  11. #211
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    Quote Originally Posted by meltingfeather View Post
    I think the drive force needs to be shown at the contact patch. It does not act at the COG, and that may be the issue.
    That took some thought. I think you are right, but I have seen that it is typical convention to show forces acting at the COG. The driving force at the contact patch pushes the bike forward, which creates a counterclockwise moment at the COG. So, if you show the force at the COG, it is pointing backwards to create the counterclockwise moment.

  12. #212
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    Quote Originally Posted by woodhzak View Post
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    I can only hope I am making a bit more sense than woodhzak

  13. #213
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    Here's a discussion about a physics problem: Calculate the rate of acceleration to cause a motorcycle to wheelie. It's a forum, so you have to wade through it, but the bottom line is the wheelie is caused by the drive force creating a moment on the COG until it overcomes the downward force of weight on the front wheel.

    Motorcycle Wheelie (Angular Momentum)

  14. #214
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    Quote Originally Posted by smilinsteve View Post
    Here's a discussion about a physics problem: Calculate the rate of acceleration to cause a motorcycle to wheelie. It's a forum, so you have to wade through it, but the bottom line is the wheelie is caused by the drive force creating a moment on the COG until it overcomes the downward force of weight on the front wheel.

    Motorcycle Wheelie (Angular Momentum)
    Yes. The "torque reaction" Mr. Wallace speaks of is the appropriate component of the weight vector balancing against the rear wheel moment. Once the moment has overcome the weight distributed to the front wheel (by putting it on the rear wheel), additional moment causes the front wheel to lift.
    The bike being on an incline gets you part of the way there by distributing weight to the rear wheel as a result of the geometry.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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  15. #215
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    Wow. This thread was so interesting to begin with. Now it is mostly confusing.

    Back on the subject of bikes, I have another idea for Geoff and Graham to consider. Its called fat front or half fat. looking at the video of the riding in the stream, I noticed a lot swaying of handle bars. Its the same in the picture too. Being a fat bike rider myself, I can say that the fat tires hold a straighter line while riding over slippery rocks. With the availability of fat bike parts being abundant, it would be easy to convert a Cleland to fat front.

    Here is a thread with pics:
    Half the Fat?

    Just something to consider.

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    Quote Originally Posted by GrahamWallace View Post
    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.



    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.



    There may be an error in my reasoning,
    If there is, I am hoping that someone will spot it and point it out.
    In the process of responding to you, I've talked myself out of my own position. I now agree that the bike rotates about the rear axle.

    In the case where the COG is in front of the axle and behind the contact patch (assuming constant cadence and no wheel slip), the bike does rotate backwards about the rear axle; the rotation is due to the force applied tangentially to the wheel at the contact patch.

    I'll butt out now.

    sbitw

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    Quote Originally Posted by sagealmighty View Post
    Wow. This thread was so interesting to begin with. Now it is mostly confusing.

    Back on the subject of bikes, I have another idea for Geoff and Graham to consider. Its called fat front or half fat. looking at the video of the riding in the stream, I noticed a lot swaying of handle bars. Its the same in the picture too. Being a fat bike rider myself, I can say that the fat tires hold a straighter line while riding over slippery rocks. With the availability of fat bike parts being abundant, it would be easy to convert a Cleland to fat front.

    Here is a thread with pics:
    Half the Fat?

    Just something to consider.
    Yes, that's right. In the video I was using 2.4" Schwalbe Racing Ralphs as an experiment with lighter tyres. As you can see, the steering is made less controllable running them at the low pressures necessary for grip and shock absorbtion. This seems mainly to be due to the thin sidewalls of the Ralphs.
    I've now fitted 2.5" WTB Dissents again, heavier tyre with thicker sidewalls, much better.
    My next move, when I can afford it, is to fit 2.75" tyres which have very stiff sidewalls and will require little or no air inside.
    I'm reluctant to go down the fat bike route for the time being until I have had a chance to try one out. That course of design endeavour will also require a new frame and lots of other stuff, so no action until I have a lot more money to hand (probably never!).

  18. #218
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    Quote Originally Posted by sagealmighty View Post
    Wow. This thread was so interesting to begin with. Now it is mostly confusing.

    > SNIP <

    Just something to consider.
    Yes, An interesting thread! I agree that it has become confusing to a bit but still interesting.
    If I may add and I will keep it simple....

    A static bike is one that has no motion or forces on it.... Once you start moving all thing change with many dynamic forces that come into play.
    Inclines, declines, obstacles, braking and pedaling all are dynamic forces, with gravity working all the time!
    Forward motion literaly starts the wheels turning. Once the wheels are rotating, gyroscopic action comes into play, using this gyro-force to your advantage can make the ride. We all started out with no intuition of how to ride a bike, usually we started with training wheels till we learn and feel comfortable with the "feel" of the dynamic bike.
    The old adage that you never forget how to ride a bike is true! but we learn more as we ride more.... for some it is a marvel how they can do these things, like Danny MacAskill! What he does is nothing short of amazing!
    I think it has a lot to do with your inner ear and it's balance system, with all these math formulas with this thread, it still comes down to skill, experience and good luck.... a flat going through a course is BAD luck!
    With the gyro-action of the bikes wheels and making use of this stabilizing force, a rider can maintain his course well using the rotating wheels to his advantage. Using the CG of the bike rider is mostly a sense of balance and becomes intuitive with practice and skill.
    Here is a link with better understanding of bike wheels in motion, gyros....

    Bicycle Wheel Gyro: Mechanics Science Project | Exploratorium Science Snacks
    Attached Images Attached Images  
    "I don't ride a bike, I'm the pilot!"

  19. #219
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    Quote Originally Posted by smilinsteve View Post
    Other than the chair, the examples are all related to shaft torque and when I google torque reaction, most hits also refer to shafts. These are obvious examples of torque reaction.
    For the bike riding up the hill, you need to draw a FBD with all forces and calculate all moments. I still think that my FBD shows all forces and moments.

    If you turn your bike upside down and turn the cranks, the cranks turn the wheel. The force of your arm applies a torque to the hub of the wheel causing it to accelerate.
    What other forces are acting on the bike?

    As for the chair, I am flapping away furiously, and not getting much movement, but want to think a bit more about this one, and hopefully no one will walk into my office.
    Lol!

    poikaa
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    Danny MacAskill video

    Just in case you have not seen Danny in action....

    Inspired Bicycles - Danny MacAskill April 2009 - YouTube

    How this applies to mountain biking? I suppose it does!

    poikaa
    "I don't ride a bike, I'm the pilot!"

  21. #221
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    If we can get past the question of does torque reaction exist? And is it relevant issue?
    q1 - I think yes, it's part of the forces you feel lifting the front as you pop a wheelie. Weight shift + torque reaction in balance - at that moment the lead foot pushes down, eight moves back and the acceleration / torque and rearward weight shift pop the front up. On a climb, your weight on the front wheel / COG overcomes the pop and you move forwards. thf Q2 - I think no, it's a smaller component in a larger force system if you climb in 'normal' balance.
    With COG at infinite height above but same position between the wheelbase, the bike wheelies again, I see the points made there. But If the COG is 'tied' to the bike, ie muscles acting in arms and legs, maybe not - muscle input mean the forces here are too complex for diagrams.

    At climbing gradient limits, torque resulting in wheelspin, or positioning on the bike compromising power output and/or balance is the issue. Or the wet/rocky/ etc terrain.
    It's all too variable and complex to model imo, but I appreciate the force diagram points as it's food for thought (and some confusion, followed by 'maybe I'll just go for a ride'!)

    Sorry If I'm simplifying. Just coming back to this after thinking about what limits climbing after a couple of rides on steeper hills. Also knowing that I'm less physicist and more ride-by-feel type )

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    Quote Originally Posted by smilinsteve View Post
    Here's a discussion about a physics problem: Calculate the rate of acceleration to cause a motorcycle to wheelie. It's a forum, so you have to wade through it, but the bottom line is the wheelie is caused by the drive force creating a moment on the COG until it overcomes the downward force of weight on the front wheel.

    Motorcycle Wheelie (Angular Momentum)
    Quote Originally Posted by meltingfeather View Post
    Yes. The "torque reaction" Mr. Wallace speaks of is the appropriate component of the weight vector balancing against the rear wheel moment. Once the moment has overcome the weight distributed to the front wheel (by putting it on the rear wheel), additional moment causes the front wheel to lift.
    The bike being on an incline gets you part of the way there by distributing weight to the rear wheel as a result of the geometry.
    Does this mean that at the point of front wheel lift, the rider moves his CoG further away from the rear axle, the liftoff would be prevented?

    And that this would happen even if the COG was only moved upwards?

    My thinking here is that a vertical movement of the CoG would reduce the effect of the rear wheel moment and so take the system out of equilibrium.

    (These are based on the precept that the rear wheel torque moment is constant so the motorbike is not accelerating).
    Last edited by GrahamWallace; 10-04-2012 at 03:15 PM. Reason: clarification

  23. #223
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    Quote Originally Posted by GrahamWallace View Post
    Does this mean that at the point of front wheel lift, the rider moves his CoG further away from the rear axle, the liftoff would be prevented?

    And that this would happen even if the COG was only moved upwards?

    My thinking here is that a vertical movement of the CoG would reduce the effect of the rear wheel moment and so take the system out of equilibrium.

    (These are based on the precept that the rear wheel torque moment is constant so the motorbike is not accelerating).
    No and no.
    The moment is countering the weight vector, specifically the component of the weight vector that is perpendicular to the moment arm (wheel radius), which does not change when the COG moves upward on level ground. It shrinks as the COG moves "upward" on a bike on an incline.
    If the COG moves forward then the moment arm increases.
    (ignore the sub D in the second force equation)
    Attached Thumbnails Attached Thumbnails Cleland: The original big wheeled off-road bicycle?-fbd-tip.jpg  

    Last edited by meltingfeather; 10-04-2012 at 08:53 PM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Just thinking about climbing a slope:
    Assuming the bicycle remains perfectly vertical, the fulcrum about which the bicycle is rotating is the rear wheel axle. Even if a wheelie does not occur, the pressure applied to the front wheel by way of rider weight transfer, is counteracting the tendency for the front wheel to lift, so there is always a potential wheelie.
    However, the bicycle does not always remain perfectly vertical, so the rider is simultaniously still conteracting the tendancy for the bicycle to fall sideways. The fulcrum for this conteraction is the contact patch of the rear wheel.
    Therefore, one must consider whether both these counteractions can be separated, or if one contributes to the other, if they interact or if in reality they can never be separated.
    Last edited by GeoffApps; 10-05-2012 at 02:14 AM. Reason: clarification

  25. #225
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    Quote Originally Posted by GrahamWallace View Post
    Does this mean that at the point of front wheel lift, the rider moves his CoG further away from the rear axle, the liftoff would be prevented?

    And that this would happen even if the COG was only moved upwards?

    My thinking here is that a vertical movement of the CoG would reduce the effect of the rear wheel moment and so take the system out of equilibrium.

    (These are based on the precept that the rear wheel torque moment is constant so the motorbike is not accelerating).
    I think a key factor missing from this perspective is the freedom of the pivot to move.
    As we have acknowledged, with the COG at infinity, the COG does not move, yet the bike tips because there is relative rotation of COG about the axle (due to movement of the pivot, not the COG).
    As the COG moves away from the axle and experiences less acceleration due to the torque reaction, the acceleration of the pivot point out from under the COG increases.
    The relative motion is what's missing from the explanations I'm seeing about smaller forces (and therefore smaller acceleration) at the COG.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    I think it would be a good time for me to try and summarize my current understanding of the factors that limit the incline that a mountain bike can climb. I hope that this will help to clarify any confusion caused by the earlier debate.

    This account is only possible because of the many earlier contributions to this discussion. Not just the contributions that have withstood detailed scrutiny, but all of the ideas that made us think hard and led us towards a greater understanding.


    KEY FACTORS INVOLVED: These factors can combine to cause front wheel liftoff. Alternately pushing too abruptly on the pedals, can cause the rear wheel to lose traction and so spin out.

    Load Transfer due to increased incline
    As the hill gets steeper load is transferred from the front to rear wheel. If the weight transfers behind rear wheel ground contact point, then even a stationary bike will flip over backwards.

    Load Transfer due to the rider moving their body-weight Moving the riders body-weight forward can compensate for Load Transfer due to increased incline. Move it too far forward and the rear wheel may loose traction and so spin out.

    The Load Transfer caused by rear wheel Torque Reaction forces( This can happen both when the bike is accelerating or climbing at a constant speed)
    According to Newton's Third Law of Motion every force has an equal and opposite reaction. This means that as a rear bicycle wheel rotates clockwise, the same torque force tries to rotate the bicycle and rider in an anti-clockwise direction. Normally the weight of the rider, pulled downwards by gravity will prevent this from happening. But if the low gear torque is powerful enough the front wheel can lift off the ground. especially when combined with the force of the Load Transfer due to acceleration of the high Center of Gravity.

    Load Transfer due to acceleration
    If a cyclist tries to accelerate in order to get to the top of a hill an additional load is transferred from the front to rear wheel that can cause the front wheel to lift off the ground. This effect is made worse because acceleration will also increase the torque being transmitted to the rear wheel and therefore the upwards front wheel reaction to it.
    Weight transfer - Wikipedia, the free encyclopedia

    The acceleration during a pedal stroke and the deceleration in-between strokes.
    If the slope is steep enough the acceleration during the pedal stroke, combined with the rear wheel torque reaction, can lift the front wheel off the ground. Motorbikes or electric bicycles with there smooth, non-pulsed, power sources do not suffer from this effect and so given enough torque will be able to climb steeper slopes than pedal cycles.

    Steep segway climb - YouTube

    A Segway is able to climb very steep slopes because is is not affected by:

    Load Transfer due to increased incline

    Load Transfer due to acceleration
    (This is because acceleration is proceeded by the rider leaning forward)

    The acceleration during a pedal stroke and the deceleration in-between strokes.

    A Segway is effected by torque reaction but this is countered by the forward lean of the rider. If the rider stops leaning forward the Segway will stop. If the rider leans to fall forward the Segway will accelerate in order to compensate.
    Last edited by GrahamWallace; 10-15-2012 at 02:55 PM. Reason: clarification

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    Quote Originally Posted by GrahamWallace View Post
    If we can get past the question of does torque reaction exist? And is it relevant issue? It may get even more Interesting
    Quote Originally Posted by james-o View Post
    q1 - I think yes, it's part of the forces you feel lifting the front as you pop a wheelie. Weight shift + torque reaction in balance - at that moment the lead foot pushes down, eight moves back and the acceleration / torque and rearward weight shift pop the front up. On a climb, your weight on the front wheel / COG overcomes the pop and you move forwards.
    I agree with that analysis

    Quote Originally Posted by james-o View Post
    Q2 - I think no, it's a smaller component in a larger force system if you climb in 'normal' balance.
    I also agree that torque reaction is a lesser issue than the acceleration and resultant weight shift caused by each pedal stroke.

    Quote Originally Posted by james-o View Post
    With COG at infinite height above but same position between the wheelbase, the bike wheelies again, I see the points made there. But If the COG is 'tied' to the bike, ie muscles acting in arms and legs, maybe not - muscle input mean the forces here are too complex for diagrams.
    Sometimes insight can be gained by considering the extreme limits of a problem, even if these are unachievable in reality. In this case the inertia and infinite leverage of an infinitely high CoG, attached via a rigid second class lever would prevent the bike from moving at all. And this ultimate example of an inverted pendulum would take an infinite amount of time to unbalance. let alone to fall down.

    Quote Originally Posted by james-o View Post
    At climbing gradient limits, torque resulting in wheelspin, or positioning on the bike compromising power output and/or balance is the issue. Or the wet/rocky/ etc terrain.
    It's all too variable and complex to model imo, but I appreciate the force diagram points as it's food for thought (and some confusion, followed by 'maybe I'll just go for a ride'!)
    True, but some times the theoretical modeling of a problem can lead to insights that can then be applied to real situations.

    I will be using the understanding gained from this discussion to further improve the climbing ability of Cleland bikes.

    The maximum slope that a current mountain bike can climb is just above 20 degrees, but a Segway can climb a 40 degree slope. Why can't a bicycle not do the same? This question has been answered here in theoretical terms but can the problem be resolved in reality. I believe that it can!
    Last edited by GrahamWallace; 10-07-2012 at 02:00 PM. Reason: Typos

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    It turns out that with the use of certain search terms like: motorbike "Load Transfer" and "motorbike squat" that there is a fair amount of information on the internet relating rear wheel torque reaction. Though almost always in relation to the effects on motorbike suspension.

    I also found this Wikipedia Talk page relating to bicycles where the learned Wikipedians also get confused.
    Talk:Bicycle suspension - Wikipedia, the free encyclopedia

    This is not the first time,that the notion that torque reaction forces are distinct from load transfer forces, has been considered in the design of a Cleland style bike. I designed this energy efficient rear suspension system in 1992.
    Cleland: The original big wheeled off-road bicycle?-suspension1992.jpg
    The rear swing arm is pointed up towards the CoG in order to neutralize the load transfer forces, whilst the torque reaction is used to counter rear wheel squat . The system was intended to have pre-loaded springs (no-sag), to eliminated vertical bobbing of the CoG.

    The gearing is in-between the twin seat tubes and the chain to the rear wheel runs inside the rear sub-frame tubing.
    Last edited by GrahamWallace; 10-07-2012 at 02:58 PM. Reason: clarification

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    Though I never built this high pivot point suspension system. But I did describe the concept in detail to a British engineer called David Wrath-Sharman whose company, Highpath Engineering, manufactured Cleland style bikes. In 2004 he made this bike called the TopTrail, that he, and car suspension designer Adrian Griffiths had enginnered.

    Name:  2004 TopTrail.jpg
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    This is a classic piece of Cleland lineage' blue skies thinking. A first class example of "first principle engineering" in which Citroen style interconnected hydro-pneumatic suspension, is adapted for use on bicycles.

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    On very rough ground, a Cleland the rider will stands bolt upright "on the pegs", whilst the front and rear wheels rock seesaw like beneath his feet. On this bike, despite the pitching of the wheels and frame the handlebars and saddle remain amazingly still. This allows the rider can remain seated and pedaling un-interupted whilst the suspension does all the work.

    High_Performance_Bike_with_Interconnected_Suspensi on.mpg - YouTube

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    Last edited by GrahamWallace; 10-09-2012 at 04:07 PM. Reason: Typos

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    Quote Originally Posted by GrahamWallace View Post
    Though I never built this high pivot point suspension system. But I did describe the concept in detail to a British engineer called David Wrath-Sharman whose company, Highpath Engineering, manufactured Cleland style bikes. In 2004 he made this bike called the TopTrail, that he, and car suspension designer Adrian Griffiths had enginnered.

    Name:  2004 TopTrail.jpg
Views: 4146
Size:  50.6 KB

    This is a classic piece of Cleland lineage' blue skies thinking. A first class example of "first principle engineering" in which Citroen style interconnected hydro-pneumatic suspension, is adapted for use on bicycles.

    Name:  5143a046b0b895845e5e5d9071faa2d2_full.jpg
Views: 2952
Size:  38.7 KB

    On very rough ground, a Cleland the rider will stands bolt upright "on the pegs", whilst the front and rear wheels rock seesaw like beneath his feet. On this bike, despite the pitching of the wheels and frame the handlebars and saddle remain amazingly still. This allows the rider can remain seated and pedaling un-interupted whilst the suspension does all the work.

    High_Performance_Bike_with_Interconnected_Suspensi on.mpg - YouTube

    Name:  2975f4dde1007255ad0bb1f966e85fbc_full.jpg
Views: 1407
Size:  24.1 KB
    Very intriguing design.
    I'm interested in how the "high anti-squat" is achieved. Since the chain and therefore chain tension (the mechanism for every other anti-squat design I'm aware of) are routed very close to the pivot point, the effect of chain tension is neutralized. In fact, with the pivot point below the chain tension vector, it appears on the surface that the design would be pro-squat. What prevents chain tension from pulling upward on the axle? The "high anti-squat angle" is cited, but without the chain tension effect I'm at a loss for how it is realized.
    Enlightenment...?
    On a related note, the explanation will probably illuminate how severe pedal feedback associated with high anti-squat is avoided on rough terrain during "uninterrupted pedaling," but I'm not seeing it at the moment.
    Last edited by meltingfeather; 10-09-2012 at 08:41 PM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Quote Originally Posted by meltingfeather View Post
    Very intriguing design.
    I'm interested in how the "high anti-squat" is achieved. Since the chain and therefore chain tension (the mechanism for every other anti-squat design I'm aware of) are routed very close to the pivot point, the effect of chain tension is neutralized. In fact, with the pivot point below the chain tension vector, it appears on the surface that the design would be pro-squat. What prevents chain tension from pulling upward on the axle? The "high anti-squat angle" is cited, but without the chain tension effect I'm at a loss for how it is realized.
    Enlightenment...?
    On a related note, the explanation will probably illuminate how severe pedal feedback associated with high anti-squat is avoided on rough terrain during "uninterrupted pedaling," but I'm not seeing it at the moment.
    The reason that I posted images of these high pivot point bikes is that the main anti-squat mechanism is the rear wheel torque reaction.

    By placing the pivot in a "sweet spot" under the CoG the torque reaction vector at the pivot can be contained. Placing the rear swing arm pivot and the center of the top chain cog was a mistake I made on my 1992 design. Consider a situation where the rider pedals hard whilst the rear brake is applied. The top jockey-wheel over which the chain is routed is prevented from rotating by the chain and the rear swing arm then acts as a first class lever with the load at the rear axle, the fulcrum at the swing-arm pivot and the input at the point where the chain rests on the jockey-wheel. This would cause the rear to squat and would also do so in other situations that create high levels of rear wheel drag like hill climbing and high acceleration. The arrangement on the TopTrail simply stops a lever being created by placing the input and fulcrum at the same place.

    The TopTrail is amazing in that it works at all. A high center of gravity bicycle with interconnected suspension where the front wheel rising causes the back to fall, should in fact, ride like a rocking-horse. The successful use of anti-dive and anti-squat systems to stabilize everything is quite remarkable.

    Many people say that this design is too complicated to build and must be heavy. But the use of carbon fiber reinforced molded sections would both reduce weight and the complexity of the space-frame.

    I did go on to build full suspension Clelands using Renault Sport's NRS system. But these behave exactly like rigid bikes until they hit a bump. The TopTrail however is much smother as it isolates the rider from not only bumps, but the pitching of the bike.

    The Toptrail Interconnected Suspension Bicycle Project

    Cleland NRS:
    [Cleland NRS 2010 | Flickr - Photo Sharing!
    Last edited by GrahamWallace; 10-10-2012 at 09:38 AM. Reason: clarification

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    Quote Originally Posted by GrahamWallace View Post
    The reason that I posted images of these high pivot point bikes is that the main anti-squat mechanism is the rear wheel torque reaction.
    To me the use of "torque reaction" is confusing and I don't yet understand how it is accurate, if it is.
    A drive force at the rear axle would cause the suspension to rise by virtue of the pivot placement. I don't see the role of "torque reaction." Even if there was no torque applied and someone were to push at the axle from behind by way of some type of yoke, the anti-squat would still occur.

    Quote Originally Posted by GrahamWallace View Post
    The TopTrail is amazing in that it works at all. A high center of gravity bicycle with interconnected suspension where the front wheel rising causes the back to fall, should in fact, ride like a rocking-horse. The successful use of anti-dive and anti-squat systems to stabilize everything is quite remarkable.
    It's certainly interesting, and takes some pretty involved mental modelling to understand. I'd love to ride one.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Quote Originally Posted by meltingfeather View Post
    To me the use of "torque reaction" is confusing and I don't yet understand how it is accurate, if it is.
    The torque reaction is proportional to the torque applied at the rear wheel whilst chain tension is dependent on the combination of cogs being used.

    Quote Originally Posted by meltingfeather View Post
    A drive force at the rear axle would cause the suspension to rise by virtue of the pivot placement. I don't see the role of "torque reaction." Even if there was no torque applied and someone were to push at the axle from behind by way of some type of yoke, the anti-squat would still occur.
    The clever bit is that the "Torque Reaction" force is being balanced against the "Load Transfer force with the weight/inertia of the rider pinning everything down. The "Torque Reaction" is trying to lift the CoG whilst the "load Transfer" forces are trying to move the CoG downwards. For this to happen the position of the rear swing-arm pivot is crucial and this was what I meant by "sweet-spot". In reality you are still left with a vertical component that when combined with the upward force of the springs will cause the CoG to lift vertically. This can be countered by damping or pre-loading the springs.

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    You should try climbing a steep hill on a modern mountain bike. Fat knobby tires, tubeless. Dual suspension, with at least 5 inches( 125 mm) of travel. Low gearing, important as to keep even steady pedaling. Most importantly, the rider. I've seen riders climb more than 20 degrees. He was on a single speed pugsly. Mind over matter. All this theory stuff is interesting but somewhat not the most important. I go on many group mt bike rides. Why on a steep section do only 3 out of 10 make it up ? Skill, technique and strength are some of the factors you are overlooking.

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    Quote Originally Posted by leeboh View Post
    You should try climbing a steep hill on a modern mountain bike. Fat knobby tires, tubeless. Dual suspension, with at least 5 inches( 125 mm) of travel. Low gearing, important as to keep even steady pedaling. Most importantly, the rider. I've seen riders climb more than 20 degrees. He was on a single speed pugsly. Mind over matter. All this theory stuff is interesting but somewhat not the most important. I go on many group mt bike rides. Why on a steep section do only 3 out of 10 make it up ? Skill, technique and strength are some of the factors you are overlooking.
    You are right about the rider skill aspect and the fact that I enjoy hill climbing is probably a factor in being good at it. The problem that the physics are complicated enough without factoring in the subtleties of riders skill. I do ride up very steep hills on my relatively modern Giant NRS Carbon full suspension bike which is pretty good despite a tendency to steer where it wants to and not necessarily where I want it to go. But it is still not as capable and assured as my un-sprung 1983 Cleland.

    The use of elliptical gearing improves the climbing limits of modern bikes as it allows for a slower cadence and reduces suspension bobbing. It also improves rear rear wheel traction and reduces the probability of front wheel lift.

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    Impressive. Looks like a modern Dursley-Pedersen!

    The 3 bike comparo on a rough track on the Toptrail site was interesting. While it's not what I'd call a rough track, it was enough to show a considerable difference. To my mind the relative silence of the Toptrail suspension would almost be worth it on its own. What I saw there overcomes most of the reasons for my dislike of suspension.
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    Quote Originally Posted by Velobike View Post
    Impressive. Looks like a modern Dursley-Pedersen!
    But in the Victorian era groundbreaking bicycle designs got manufactured. Today the British cycle industry is content to churn out the same old designs whilst proclaiming minor improvements as major developments.

    The TopTrail is unique in being a collaboration between top automotive suspension designer Adrian Griffiths, and the ingenious British mountain bike pioneer/engineer, David Wrath-Sharman. David who was pictured at the very beginning of this thread riding a Cleland certainly knows how to ride off-road. So despite the lack of challenging riding shown on the TopTrail website, this bike is bound to be a highly capable machine.

    I wonder how many "industry" bicycle designers would understand this design?
    And I severely doubt that any could be this inventive and creative.

    Will the TopTrail or an updated version ever be manufactured?

    I very much doubt it.

  38. #238
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    Quote Originally Posted by meltingfeather View Post
    To me the use of "torque reaction" is confusing and I don't yet understand how it is accurate, if it is.
    Amen brutha.

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    Quote Originally Posted by GrahamWallace View Post
    I think it would be a good time for me to try and summarize my current understanding of the factors that limit the incline that a mountain bike can climb. I hope that this will help to clarify any confusion caused by the earlier debate.
    Most of your summary is ok. I'm not going to go through it. It seems however that you have not progressed at all in your thinking about torque reactions, so I will quit trying, but to respond to this:


    Front wheel lifting caused by rear wheel torque ( This can happen both when the bike is accelerating or climbing at a constant speed)
    According to Newton's Third Law of Motion every force has an equal and opposite reaction. This means that as a rear bicycle wheel rotates clockwise, the same force tries to rotate the bicycle and ride anti-clockwise.
    NO.

    You posted somewhere earlier that you could push on a rear wheel and make the front end of a bike lift off the ground. Well, post the youtube video showing this. I'm not going to argue, just make it happen.
    When you understand that this is impossible, you wil have a better understanding of the foces on the bicycle, and you will have to revise your "torque reaction" theory.

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    SmilinSteve, I had to dig this up. Have you ever learnt how to wheelie? Dropped the clutch on a motorcycle with a heavy throttle? Stood on the pedals on a steep incline taking off with a rear loaded bicycle?

    I can show you a video with a rear hub motor electric assist bicycle doing the "torque reaction" wheelie at the twist of a throttle (pushing the rear wheel forward) and makes the front end lift off the ground (aka a wheelie). Heck even the opening scene of On Any Sunday by Bruce Brown, THE motorcycle documentary, demonstrates this. Youtube it

    It seemed so obvious and well demonstrated in practice, I couldn't see the confusion and assertive "NO" and impossibility.

    I'm amused at the death of a great thread that for your 7,533 posts, Graham only had 171 posts, and had joined the year prior to you. Perhaps being ridiculed and challenged to prove some simple physics isn't how he likes to spend his spare time. Just a theory, maybe you could prove it to me

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    Torque reaction in bicycles explained

    Whilst contributing to this thread it occurred to me that torque reaction forces in bicycle drive chains could theoretically be used to smooth out the substantial fluctuations in power caused by the ever changing angle between the foot and the cranks. I also thought that by fully explaining the mechanism that causes torque reaction in bicycles, I would maybe help others to reach the same conclusion. And so chose not to explain the phenomenon of "Torque Reaction" beyond the basic principles.

    Now, having long since fully explored the real world applications of torque reaction in bicycles and discovered nothing worth patenting, I'm am now happy to explain in more detail. And maybe even post a video showing the phenomenon, if that proves helpful.

    First of all we have to realize that there are two separate forces involved in creating a bicycle or motorbike wheelie. Three if you also include pulling up on the handlebars.

    The usual explanation for motorbike wheelies is called load transfer.
    Weight transfer - Wikipedia, the free encyclopedia

    Load Transfer or Weight Transfer
    Because the drive forces acting at the rear tyre contact patch are lower down than the vehicles "Centre of Mass" (CoM), the front of the vehicle will try lift upwards during acceleration due to the upward direction of the propelling force. So effectively the load transfers from the front to the rear wheel until there is no longer any load on the front wheel and it lifts off the ground.

    Torque Reaction
    Torque reaction is easily confused with "Load Transfer" but the mechanism is totally different. Torque Reaction is an inherent property of a chain drive mechanism and but unlike "Load Transfer" it does not require acceleration or even any forward movement of the bicycle.

    Explanation
    The bicycle drive-chain mechanism consists of two inputs the pedals, the mechanism itself, and the output at the rear wheel. However if you constrain the output by say bolting the rear wheel to the ground, where will the power go? It does in fact turn out to have another means of escape because if the tension in the chain cannot rotate the rear wheel relative to the bicycle, given enough force it will rotate the bicycle relative to the wheel. So an attempted, say clockwise, rotation of the rear wheel instead results in an anti-clockwise rotation of the bicycle and rider around that wheel.

    So a wheelie is usually caused by varying combinations of "Load Shift", through acceleration, and "Torque Reaction" resulting from the rear wheel resisting rotation. However, a steep hill start where the front wheel lifts without the bicycle an rider even moving forward is entirely due to Torque Reaction.
    Last edited by GrahamWallace; 05-25-2015 at 03:57 PM. Reason: claricication

  42. #242
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    Quote Originally Posted by GrahamWallace View Post
    Whilst contributing to this thread it occurred to me that torque reaction forces in bicycle drive chains could theoretically be used to smooth out the substantial fluctuations in power caused by the ever changing angle between the foot and the cranks. I also thought that by fully explaining the mechanism that causes torque reaction in bicycles, I would maybe help others to reach the same conclusion. And so chose not to explain the phenomenon of "Torque Reaction" beyond the basic principles.

    Now, having long since fully explored the real world applications of torque reaction in bicycles and discovered nothing worth patenting, I'm am now happy to explain in more detail. And maybe even post a video showing the phenomenon, if that proves helpful.

    First of all we have to realize that there are two separate forces involved in creating a bicycle or motorbike wheelie. Three if you also include pulling up on the handlebars.

    The usual explanation for motorbike wheelies is called load transfer.
    Weight transfer - Wikipedia, the free encyclopedia

    Load Transfer or Weight Transfer
    Because the drive forces acting at the rear tyre contact patch are lower down than the vehicles "Centre of Mass" (CoM), the front of the vehicle will try lift upwards during acceleration due to the upward direction of the propelling force. So effectively the load transfers from the front to the rear wheel until there is no longer any load on the front wheel and it lifts off the ground.

    Torque Reaction
    Torque reaction is easily confused with "Load Transfer" but the mechanism is totally different. Torque Reaction is an inherent property of a chain drive mechanism and but unlike "Load Transfer" it does not require acceleration or even any forward movement of the bicycle.

    Explanation
    The bicycle drive-chain mechanism consists of two inputs the pedals, the mechanism itself, and the output at the rear wheel. However if you constrain the output by say bolting the rear wheel to the ground, where will the power go? It does in fact turn out to have another means of escape because if the tension in the chain cannot rotate the rear wheel relative to the bicycle, given enough force it will rotate the bicycle relative to the wheel. So an attempted, say clockwise, rotation of the rear wheel instead results in an anti-clockwise rotation of the bicycle and rider around that wheel.

    So a wheelie is usually caused by varying combinations of "Load Shift", through acceleration, and "Torque Reaction" resulting from the rear wheel resisting rotation. However, a steep hill start where the front wheel lifts without the bicycle an rider even moving forward is entirely due to Torque Reaction.
    Well this is a blast from the past. Graham, unfortunately you offer nothing new since your 2012 posts and you are still wrong. I'll say the same thing I said in 2012 also. Post a YouTube video and show that you can fix a rear wheel to the ground, push on the crank and make the front end lift. It will never happen. It's impossible. Instead of 3 years of confusion, you could have done a 15 minute experiment to help you find the truth in this.

    The only points of attachment between the drive train and frame are at the bottom bracket and the rear dropout. Both these are attached by bearings so no torque can be transferred to the frame. Zero.

  43. #243
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    Quote Originally Posted by deepfraught View Post
    SmilinSteve, I had to dig this up. Have you ever learnt how to wheelie? Dropped the clutch on a motorcycle with a heavy throttle? Stood on the pedals on a steep incline taking off with a rear loaded bicycle?

    I can show you a video with a rear hub motor electric assist bicycle doing the "torque reaction" wheelie at the twist of a throttle (pushing the rear wheel forward) and makes the front end lift off the ground (aka a wheelie). Heck even the opening scene of On Any Sunday by Bruce Brown, THE motorcycle documentary, demonstrates this. Youtube it

    It seemed so obvious and well demonstrated in practice, I couldn't see the confusion and assertive "NO" and impossibility.

    I'm amused at the death of a great thread that for your 7,533 posts, Graham only had 171 posts, and had joined the year prior to you. Perhaps being ridiculed and challenged to prove some simple physics isn't how he likes to spend his spare time. Just a theory, maybe you could prove it to me
    rotation occurs at the rear axle. When you hit the gas on a motorcycle, there is a forward force below the axle at the contact patch and a rearward force caused by the acceleration of the center of gravity above the axle. This force couple causes the rotation. Note these forces are horizontal. There is no torque reaction.

    Glad you are amused and impressed with my post count. I'm just talking physics, and will be happy to add a few more posts to my count if you need more help.

  44. #244
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    Quote Originally Posted by smilinsteve View Post
    ...I'm just talking physics, and will be happy to add a few more posts to my count if you need more help.
    I'm interested in getting bikes working better, so I'm keen to see more practical experimenters like Graham publishing their efforts rather than see them getting discouraged by theoreticial purists - "That may work in practice, but it doesn't work in my theory, so it can't be true"

    With your advanced knowledge of physics, perhaps you could tell us about what you have done to make bikes better?
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    Cleland: The original big wheeled off-road bicycle?

    deleted due to theory fail.
    Last edited by meltingfeather; 06-04-2015 at 08:35 AM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Edit: original post deleted. It's pointless.

    I'd sooner see folk like Graham who build stuff posting than listen to lectures on theoretical semantics.
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  47. #247
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    Quote Originally Posted by Velobike View Post
    I'm interested in getting bikes working better, so I'm keen to see more practical experimenters like Graham publishing their efforts rather than see them getting discouraged by theoreticial purists - "That may work in practice, but it doesn't work in my theory, so it can't be true"

    With your advanced knowledge of physics, perhaps you could tell us about what you have done to make bikes better?
    I appreciate Graham's designs and thoughts, and have been enlightened by him to a certain extent in this thread (from what I recall, I haven't gone back and reread the whole thing). The whole concept of high center of gravity and upside down pendulums, for example, was new to me and an interesting concept.
    Discussions about physics however, are discussions about physics. I know some people are bored or uninterested or have a revulsion for the science being discussed. You don't have to like it, or to read it. What I have done to make bikes better is a non sequitur.

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    Quote Originally Posted by GrahamWallace View Post
    I get it.
    I was wrong... hitch in my thinking.
    My apologies... keep at it, Graham!
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
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    Cool-blue Rhythm

    Quote Originally Posted by meltingfeather View Post
    I get it.
    I was wrong... hitch in my thinking.
    My apologies... keep at it, Graham!
    It is interesting to note that your and Steve's questioning of my thinking has helped me to gain a deeper understanding of why it happens.

    It's remarkable to think, that after over a hundred years of the bicycle evolution, there are still things to discover that haven't yet been included in the bicycle science' books. Though I can't be the only person designing suspension systems for bicycles, to notice this weird property of the bicycle drive chain mechanism.

    It's a shame that my attempts to find a useful application for this property were unsuccessful. Perhaps someone else may also like to try?

    I am currently exploring what will hopefully turn out to be more fruitful lines of research, which I unfortunately can't talk about freely at present. And though It is relatively easy to redesign the bicycle, it is extremely difficult to make one that performs better than the best earlier designs. That said, I don't believe that the bicycle designs we currently have are optimal for all riding conditions.

    Best Regards,
    Graham
    Last edited by GrahamWallace; 06-04-2015 at 11:45 AM. Reason: clarity

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