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  1. Today
  2. Can Weight Shift Theory be debunked?

    You are welcome, Jaybird What you have been analyzing and trying to understand is very complex dynamics, reason for which most riders don't even bother learning the "why" of these things. The books that explain the whole interconnection of steering, wheels, masses, forces, etc. in a motorcycle are very dense to read and difficult to comprehend. I believe that there is value in understanding the basics of the Physics behind riding a motorcycle in a proficient way. It is difficult to explain those principles to inexperienced riders without going too deep into the subject and causing confusion. Most mentoring/teaching is limited to "do this to achieve that and go practice it". The experienced rider has the advantage of having tested what works and what does not, of having felt those forces and the reactions of the machines during enough time to make sense of those principles. If serious about this, by persistent observation during thousand of miles, an educated rider becomes more aware and more sensitive about the dynamics of riding and develops a finer input of all the controls and sense of balance. The Physics then becomes less abstract and more in harmony with our senses and minds. In order to function as a motorcycle rather than as a bag of potatoes, all the forces and moments acting over a motorcycle in different directions must be in balance. If our control inputs or road conditions break that balance, a brief transition period follows, during which the machine does its magic to self-adjust to a new state of balance. If that state is not physically achievable, a fall will follow. Counter-steering is a clear example of that: the rider intentionally steers the bike out of balance (out of its rectilinear path), inducing many reactive forces, movements and moments for a very brief period of time, forcing the machine into a new state of balance (onto a curvilinear path). If the machine continues on in one of the two states of balance, the rider is doing nothing or too little to modify those, like it happens in the No BS bike demonstration. If the machine is upset by incorrect control inputs from the rider, like closing the throttle during a big rear tire slide, the machine can go from stable cornering balance to unstable transition to out of balance (highside fall) really quick. The speed of the motorcycle is very influential about the steering, gyroscopic reactive forces, rolling and balance, reason for which counter-steering is so powerful in a superbike at high speeds, but almost negligible for a trial bike at walking speeds. http://www.dynamotion.it/eng/dinamoto/8_on-line_papers/effetto giroscopico/Effettigiroscopici_eng.html
  3. Yesterday
  4. How Much Weight On The Seat?

    Makes it difficult for the front tire to follow the contour of the road.
  5. Can Weight Shift Theory be debunked?

    Thanks @Hotfoot and @Lnewqban for allowing me to work through this. I realized after re-reading this and a few other threads, thinking and letting it all sink in that I had been conflating separate movements of the bike. So I'll wrap it up thusly and perhaps bring this thread to a close. I've been thinking about this new chapter (I could almost swear it wasn't in my book before- LoL) and it seems that there's a jewel in there about the bike steering about the rear wheel (once leaned over). I realized that I'd been conflating the concept of a longitudinal rolling motion (leaning) the bike and the result of changing the bikes directional vector (turning). We can do all types of things to try to get the bike to follow a corner, but ultimately it's the result of the smaller circular circumference of the rear tire that makes the nose of the bike point in the direction with the lean, just like a coin standing on it's edge rolling in a circle. If this is true, the act of leaning and turning are 2 separate behaviors and are about different planes of motion. The leaning would be a roll about the longitudinal axis and turning would be a lateral movement or yawing motion about what is often referred to as Z- Axis. But these are still 2 separate changes of state of motion. I apologize if I caused anyone distress (other than myself). Eventually...I suppose, I'll figure the Motorcycle Theory of Everything (MToE).
  6. Can Weight Shift Theory be debunked?

    That helps a lot, yes.
  7. Last week
  8. Experiments with Shifting Gears and Turn Radius

    Clicked on the Stoner book and tried to find it in print version. Not available until Nov 2018!!!!
  9. Can Weight Shift Theory be debunked?

    With effective leverage only basically parallel with the road and feet in an awkward (forward) position, this guy can describe to you pretty readily what makes his bike change direction This guy however, with his bodyweight over the steering stem may have a different perspective on what makes the bike change direction When I was at the school last year, Dylan explained in a way that I thought was brilliant (for me at least) what Keith actually described but didn't use the same words in TOTW. Keith used the word "countersteer" and then described the action of the front wheel tracking the trajectory of the turn. Dylan used the words, "countersteer" and "prosteer" in the same sentence and I had an "Aha! moment". A read through some writings dismisses as negligible any effect of bodyweight on the influence of steering. I posit that there are too many riders doing things with their weight on the bike to dismiss it and I think some of the absolutism may be obscuring the effects we have on the ability to steer a motorcycle through different intentional means. The reason I started this thread was because I didn't want to muddy another thread where I saw glimpses of the poster perhaps getting some traction in this vein until the thread got derailed and rather than reopen a can of worms, I settled on a cleaner path. As anecdotal proof of combined effort, (that's often cited) Dani Pedrosa is known for using the Hook Turn technique at corner entry and throughout the remainder of the turn. He uses it in combination with his steering input to get the desired result. Being a school, I understand (and support) clearly the many reasons why it would be desirable to teach and emphasize countersteering then (relaxing input and) prosteering (by the bike's geometry) as a primary means of control. I hope that my intentions are now made clear.
  10. Can Weight Shift Theory be debunked?

    Talking about chairs, it has occurred to me that we can discuss the actions of monkeys (passengers) in sidecars races. By moving around for each corner, they do what you describe about your folding chair: they relocate the total or combined center of gravity as far from the motorcycle or as close to the rear tire as possible. Rather than trying to make the motorcycle and sidecar roll, they compensate the natural rollover tendency during fast cornering as much as possible. That rollover tendency is induced by the combination of centrifugal effect and height of the center of gravity respect to the road. A regular sidecar could be comparable to the situation that you have pictured above: a motorcycle with a dramatic asymmetrical weight to its side. Would the bike yield to the induced roll? Let's say that thanks to the third wheel, that weigth does not roll the bike over and instead keeps it vertical. If we weld the steering to the frame keeping the steering bar perpendicular to the bike and then make the bike and sidecar gain speed on a straight trajectory, the contraption will describe a straight line. As the bike happily cruises along, if we suddenly remove the sidecar wheel, even with the stability induced by the two remaining main gyroscopes of the contraption, that asymetrical mass or weight will be able to roll the bike until the sidecar axis hits the ground (the lateral balance will be lost). The bike, even while leaned over, will try to keep going along the straight line (assuming no dragging forces from that dragging axis) because the steering has not changed. Riding with a Motorcycle Sidecar: http://www.steves-workshop.co.uk/vehicles/bmw/sidecar/riding/sidecarriding.html Yes, a substantial weigth with some lateral leverage is able to roll a motorcycle in movement or tip the stationary chair of your example over. Nevertheless, without the complicity of the steering capability, the bike will not turn, even if leaned over. The following video shows that the steering capability of a motorcycle, with or without a sidecar, has a powerful influence regarding directing it onto either a straight or a circular trajectory in a precise and controlled manner ....... and what it seems more important: combined with speed and rider's skill, it is able to lift that asymetrical weight and keep it balanced at will, even on a left turn, in which the centrifugal effect tries to take the chair down. The maneuver is known as "flying the chair". https://www.youtube.com/watch?v=k6ZSSPY32Jk
  11. Can Weight Shift Theory be debunked?

    Nice post, Lnewqban. Jaybird, what is it that you are trying to fix or figure out? We know from riding our no BS bike at the school that you can get a bike to drift to one side by hanging weight off to one side - as Lnewqban addresses quite well above. But we also know that it is slow and imprecise, and anyone who has ridden the no BS bike recognizes immediately that they are not in control of the motorcycle when their hands are on the fixed bars. Given a slow enough speed and enough time and space to accomplish it, you can get the bike to turn, but it is hardly effective enough to get one around a racetrack or avoid an obstacle. You can see a clear demonstration of this in the Twist II DVD, you can see the effects of weight shift, how the the bike reacts and how the bars react. I'm not quite clear whether you are trying to address hanging weight off to the inside, or talking about weighting one peg without moving the Center of Mass, the effects are different. More importantly, what challenge are you facing in your riding that has you asking about this? (Or is it all just an academic dicussion ? )
  12. Help - How to learn/start using knee sliders??

    Some other tricks... rain sliders are thicker and touch down sooner, and there are also leather sliders that make a less startling noise when they scrape.
  13. Experiments with Shifting Gears and Turn Radius

    https://motomatters.com/interview/2012/04/12/casey_stoner_explains_how_to_slide_a_mot.html Casey Stoner Explains How To Slide a MotoGP Bike: "It's something that only works in certain corners in this type of racing, it doesn't work in all the corners. When it does work, sometimes it can be a bit scary; you can go into the corner, and if you make a small mistake when you are sliding, the finish of it can be a catastrophe. When your heart beats really hard is when you slide when you don't really want to,"....... "There's different techniques to different corners and when they should be used, depending on grip levels, and a lot of different things. Unfortunately, most of the time these days, sliding is not the fastest way, there's only some corners where it can still work." About teaching a 5-year child how to shift gears, I recommend you this reading: https://books.google.com/books/about/Casey_Stoner_Pushing_the_Limits.html?id=npA1AgAAQBAJ
  14. Development

    @faffi- Did you find what you were looking for?
  15. Help - How to learn/start using knee sliders??

    You are correct. Expectations dispel surprises!
  16. Can Weight Shift Theory be debunked?

    Grab a folding chair and sit backwards so you have somewhere to put your feet. The mass of the system equals yourself and the chair. Scoot over far enough and the chair tips. I’m willing to ponder that a motorcycle behaves similarly, even with those black gyroscopes spinning.
  17. Help - How to learn/start using knee sliders??

    Interesting point! Cheers! One of the reasons that I didn't want to use my knee as a lean angle gauge is that when your knee touches down, it doesn't mean that you can't lean any more. I prefer to spend my attention on feeling traction at the tyres and use that as my gauge. But I guess I'll just have to make an effort to try and stop pulling my leg in towards the bike... if you expect your knee to touch down, that means it can't surprise you, right?!?
  18. Mid-Corner Countersteering

    This point caught my attention... how many people actually use the rear brake to tighten their line?? No one. Rear brake does not tighten line, if it seems that way it's because there is always additional rider input beyond simple rear brake actuation - such as body position change, handle bar input etc. So don't worry, you're not doing anything wrong and you're not missing out on anything. On the point of not having confidence in the front tyre - if you look at any mid-corner crash that doesn't involve throttle, there is almost always brake involved. Therefore if you remove the use of brakes, you remove a big portion of any chance of error. Taking it a step further - do you know how quickly you can steer the bike (given dry & smooth track, warm tyres, etc.)? You can steer it as fast as you want and the front won't give out/fold/slide. What will happen is that the rear will slide when you start to get to that limit. So if you're steering as fast as you can and there's no hint of the rear sliding, you are safe. Actually I think Keith Code has said that he's tried to crash a bike by using a "too fast" steering rate and he couldn't do it. So that should give you some confidence! Taking that and applying it to a double apex/hairpin type situation, if you remove the main danger (brakes), and you know that you can use as quick a steering rate as you want it opens up a whole world of possibilities. You can carry more speed into the turn, stay out wide and basically ignore the first "apex", it will set you up for a good exit. At least that's my approach now and it's helped a lot! I was in the habit of treating these types of turns as 2 separate turns with additional steering input in the middle, now it's so much easier when you can ride it as a single turn with one smooth steering input. If there is slightly more distance between the "2 apexes" it might mean that you need to tighten your line, but this is more of a continued steering input, definitely no brake or throttle in the middle. For this approach to really work it does mean that you need to carry a lot of speed into the turn, possibly a lot more than you're used to, but just remember that the very act of turning will reduce your speed and tighten your line, and you also have the option to tighten your line with line with continuous steering input as well as technique such as hook turn - when you put all of that together you can really start riding some much smoother and easier lines.
  19. Help - How to learn/start using knee sliders??

    No “advice” but here’s a little story from my experience: First time my knee came down was on a relatively tight and track- ViR Patriot about 2007. It was my last session of the day and I’d been talking with the guy pitted next to me and we thought that the track might have been too slow to get knee down. So we dismissed the notion. I was doing well, hitting my marks and in T3 (after the eases) I felt something brush my thigh. About a half lap, I realized it was the ground. I decided I’d better stick my knee out instead of tucking into the bodywork. Next lap on T3 I felt it graze the slider and I realized that just a bit more speed and it would probably happen. Grazed the slider again on next lap but again added more speed and it came solidly down. I began to look for and expect it on subsequent laps and began to understand why people refer to it as a lean angle gauge. It also became a point of timing for me that I could roll on the gas.
  20. Can Weight Shift Theory be debunked?

    Unless you have a fixed fulcrum to exert leverage against, you move the bike away from you (roll it a little) as you move your body off in the opposite direction. The total center of gravity (yours plus bike's) remains along the vertical line that crosses the imaginary horizontal line that connects both contact patches. If the steering is kept perfectly fixed and aligned with the contact patches, the bike does not have a reason to turn. If instead the steering is free to adjust by itself, the geometry of the front tire and angle of suspension, combined with the total weight and gyroscopic reaction (please, refer to your video and see that a left roll of the bike induces a left steering) , will slowly turn the steering towards the side upon which the bike has rolled (only if steering angles, tire's profile and pressure are neutrally set, so there are no over or under-steering tendencies). That slight counter-steering will induce a balancing slow roll towards the side upon which the rider is hanging off and the bike will commence a turn. That is the same self-balancing principle that allows a rider-less bike keep going for a while while speed is relatively high. That is a very different situation than exerting "a force (weight) at a lever point away from the center of rotation". We are starting from an out-of-balance situation. In that case, the bike will be forced to roll due to the moment created by the total center of gravity being initially far away from the line that connects both contact patches. Either or not the self-balancing capability of the steering will be strong and fast enough to compensate for that initial lack of balance depends on several factors, such as magnitude of off-set weight, weight's lever, mass of front tire and linear speed of the bike.
  21. Experiments with Shifting Gears and Turn Radius

    Perhaps we should have been discussing this instead. Only corollary that I could think of would be Garry McCoy’s sliding style of cornering, where he’d light up the rear, swinging the thing around the steering head. Caught a lot of flak until he won a GP race like that AND it was found that the tire was no worse for wear as only the top surface was heating up.
  22. Experiments with Shifting Gears and Turn Radius

    Thank you. No problems here.
  23. Experiments with Shifting Gears and Turn Radius

    I perceived that you felt a need to clarify for my sake- that I missed something in translation. Did I misunderstand that you thought I misunderstood? (LoL)
  24. Experiments with Shifting Gears and Turn Radius

    Absolutely! That is the whole reason for the need of selective gears: to keep the engine rotating within the range of rpm's that produces usable torque (and work) for a wider range of rpm's of the rear wheel (which translates into forward speed of the motorcycle). Except during the brief periods of coasting and engine breaking, the work of the engine pulls the motorcycle forward against the resisting forces of inertia (during acceleration) aerodynamic drag (at relatively high speeds) and (when climbing a hill) gravity. The only thing that dramatically changes the torque (and work) that the engine can deliver is the "twist of the throttle": more entering fuel and air means more powerful internal combustion, which means more internal heat and delivered torque (and work). That is true for certain range of engine's rpm and until we reach the point of full open throttle (maximum intensity of combustion and delivered torque), which is what dyno charts show. The work developed by the rear tire is always the product of its rotational speed (rpm's) times the torque it is able to deliver, which is exactly the same value as the product of its linear speed (forward speed of the bike) times the rearward force exerted over the pavement. The value of the work developed by the engine is always a little higher than the previous one, as some energy (in the form of transferred forces down the gears and chain and sprockets) is lost in the links between the crankshaft and rear tire. When the bike is moving at sustained 60 mph on a horizontal road, the position of the throttle is fixed, allowing intake of the exact amount of fuel and air that keeps two forces in balance: pushing forward force and resisting rearward force. If the bike starts climbing a hill and the throttle remains fixed (work delivered by the engine remains the same), the force resisting the rotation of the rear wheel increases due to the addition of the gravity effect. As no additional work from the engine is available, the other factor of the formula (torque X rpm) must decrease, resulting in a new state of balance at lower rpm's. The natural reaction to that is the slowing down of the rotational speed of the rear tire and forward speed of the motorcycle and reduction in rpm's of the engine. We can only allow certain amout of that reduction of the rpm's of the engine before the engine becomes real weak. If we wish keeping the same on-flat-road during the climb, we need to open the thottle up (more work delivered by the engine translates into resuming speed). If the steepness of the hill is excessive to achieve a new state of balance, even at full open throttle (no additional available work), we need to sacrifice bike speed in order to increase force on the rear contact patch via dowshifting. Returning to your original question: When the bike is moving at sustained speed on a horizontal road, the two forces are in balance: pushing forward force and resisting rearward force. If you open the throttle up some (more delivered work), the bike will accelerate due to additional torque reaching the rear tire, until reaching a new rpm X torque balance. If you open the throttle up a lot, the bike will do a wheelie due to excessive acceleration and abundant traction. If traction is not that abundant, then the additional available work must go to break the grip between the contact patch and the surface, spinning the rear wheel.
  25. We Got An HP4 Race!

    WOW!! Very nice!
  26. Experiments with Shifting Gears and Turn Radius

    Wouldn’t the changes in leverage be experienced at the power plant end of the system? If traveling at any given speed in the 1st gear does the road, tire, wheel, sprocket, chain or countershaft know the difference between doing the same speed in 4th gear? I haven’t seen enough to be convinced that those forces are different, save for the power pulses (maybe); the same amount of WORK is being performed despite the advantages of leverage.
  27. I just did a track day, and during the day I got to thinking that I really need to start using my knee sliders and get comfortable using them. After a lot of big improvements in quick succession (suspension upgrades that gave much better feel & improved confidence, started using tyre warmers so I gun it into the first corner and don't waste time) I've found myself getting surprised the few times a knee slider touches down. Sometimes it's just because my inside leg bounces and the slider almost "slaps" the track over a bumpy section, other times it's just that I'm carrying that much lean angle. I've never focussed on getting my knee down, I've spent all my time working on other areas of my riding which is finally all coming together and paying off big time! Speed is not a problem, today was the first time I rode in the fastest group and I probably should have been there for a little while. I am probably the only person in the group that doesn't get knee down. But my riding style means that I don't have such an exaggerated "leg out" body position, in fact usually I pull my leg in towards the bike. So I'm never expecting it when the slider touches down and it has been catching me off guard, sometimes I actually check up and roll off the throttle slightly, which then puts me off and I loose the rhythm for the rest of the lap and a bit. So the question is - how do I go about getting used to using the knee sliders? Just keep doing what I'm doing... and try to get used to the feeling when it happens? It feels like I'm backwards with all this - usually people put all their effort into getting knee down to look cool, then focus on actually developing good riding technique - I went straight to the technique, "cool factor" be damned. Haha Has anyone else found themselves in this situation - being fast, but totally unfamiliar with getting your knee down?? Cheers for any ideas or suggestions!
  28. Can Weight Shift Theory be debunked?

    Yes. Hang off to one side and the bike rolls (per your diagram above).
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