# Lnewqban

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2. ## wrong push on external handlebar

Gianco, why do you think that pushing on external handlebar while cornering is wrong? Some bikes are naturally under-steering, yours may have that tendency for the tires that it is wearing. That means that the front tire will try to under-steer by itself when leaned. By keeping pressure on the external handle, you are compensating for that tendency and keeping everything in balance. You know exactly how much pressure to keep by feeling the bike balanced while cornering (not falling into the turn or out of it). Whenever you are "too slow for that moment" or at the ideal cornering speed, the bike is leaning exactly what it needs to lean to keep lateral balance of forces for that particular speed/radius-of-turn combination. As soon as you released the external pressure that was necessary to compensate for the under-steering tendency of the bike, a small counter-steering happened by itself (the internal handle-grip moved forward some), which leaned the bike excessively for that speed and you immediately felt the bike was falling into the turn (the lateral balance of forces had been ruined). Remember, we never directly select the lean angle, we only choose speed and radius of turn; then, the bike leans as far as it needs in order to find the lean angle that balances all lateral forces. By hanging-off we reduce the lean angle of the chassis, but the dynamic lean angle of balance (of the combined center of mass) remains the same for same speed and trajectory of the curve/radius of line.
3. ## dynamic theory

You are correct, Gianco. It is about covering the course as quickly as possible, using street tires only. The riders need to go fast between cones (or pylons), braking-in and accelerating-out very hard as well; that is why they install bigger than normal rear sprockets. Around the cones the situation gets reversed and they need to go slow to rotate (change directions) as quickly as possible. They don't discuss cornering mph, but degrees of rotation per second. Because centrifugal effect depends on the square of velocity and on inverse of radius, at very low velocities the radius becomes much more important in that equation. If the rider reduces the radius to a minimum without quickly slowing down (as much as needed), the centrifugal effect will flip the bike out of the turn (bassically an out of control counter-steering). At full lock (no chance to steer), the balance is achieved by braking (more lean angle and tighter circle) or accelerating (less lean angle and wider circle). Of course, moving the upperbody in or out also changes lean angle and radius of turn (low speed = small gyroscopic effect), but main balance is carefully achieved by controlling a very accurate slow speed during a critical section of the circular trajectory. Either or not parts of the chassis drag over the pavement is a consequence of all the above: proficient Gymkhana riders don't need or purposely look for maximum lean angle. For more information about these techniques, please see: http://amgrass.com/forum/index.php https://www.youtube.com/watch?v=8ZFdxEWpefI
4. ## dynamic theory

The﻿ book that you have mentioned has the answer to your original question: "What makes the bike turn the same as it was leaned more without hanging off? It is exp﻿lained in Chapter 3: Less lean angle requires more effective steering angle in order to keep the same radius of turn (please, see figure 3.18 of page 3-13): "Increasing lean angle tends to increase the effective steering angle." It is a simple geometrical problem, there is no need to complicate it with camber thrust, slip angles, etc., because the magnitudes of the forces of cornering and the dynamic lean angle remain the same, either or not you hang-off. The chassis reduces its le﻿an angle when the rider hangs-off while cornering, which changes the relative geometry among the three planes: the ones containing the rear tire, the steered front tire and the curve (track surface). ﻿ You may want to do the following experiment: Fill up a wide recipient with water (the surface of the water will work like the plane of the curve). Make a central 10-degree bend in a small rectangular piece of cardboard (one side will work like the plane containing the rear tire and the other side like the plane of the front ti﻿re). Keeping the bent edge and both sides vertical, deep the piece of cardboard into the water. Looking from above, turn the cardboard just like a bike would lean over ﻿to﻿﻿ turn and note how the angle formed between both lines that intersect the surface of the water and each side of the cardboard g﻿ets bigger a﻿s the lean angle increases. That angle is the effective (or kinetic) steering angle, which would force the bike to turn tighter (﻿reduc﻿﻿e﻿﻿d﻿ radius of turn) if the rider would not compensate for this phenomena by steering a little less.﻿ If that experiment still does not convince you, we could use the following well stablished formula: Radius of turn = [Wheelbase x Cosine of chassis lean angle] / [Steer angle x Cosine of caster angle] As wheelbase gets a little bit smaller and caster angle remains constant, when the rider hangs off while cornering, the cosine of the chassis lean angle increases (example: cos 45=0.707 and cos 40=0.766).﻿ That change would increase the radius of turn some, making the bike run wide respect to the desired trajectory. In order to avoid that from happening, the rider must compensate by increasing the steer angle a little. Another﻿ geometrical way to analize that: Imagine a perfectly vertical line running underground by the center of the circular trajectory of the motorcycle. Disregarding slip and camber thrust, the extended axis of both wheels must intersect with that vertical line. As those wheels are leaned more, the point of intersection moves deeper into the ground, which reduces the angle formed between the e﻿xtended axis of both wheels. Hence, the steering angle must be reduced some in order for the bike to keep tracing the same circular trajectory. ﻿﻿ A leaned motorcycle will always have an effective steering angle that is smaller than the one for a 4-wheel vehicle describing the same curve. ﻿ The exercise of Motorcycle Gymkhana is a different solution to a problem that is different: make the tightest quick turn around a cone. The maximum speed at maximum lean angle will make you slower in this particular case, try that experiment as well. Since speed must be much smaller than during normal Superbike track cornering, the smallest radius of turn of the rear tire is the key to turn the bike 180 degrees as quickly as possible. For the same reason explained above, the Gymkhana rider wants the chassis to be as leaned as possible during the slowest section of the tight turn.﻿ At full stop lock of the steering, the radius of turn (and the circular trajectory of both tires) will be smaller as the chassis lean angle increases: there is a greater effective steering angle.﻿ Lock the steering of a bicycle at a pronounced angle and push it while at different sustained lean angles for each completed circle and you will see that the smallest circle corresponds with the biggest lean angle. For the above formula and description of angles, please see "Steering angle" here:﻿﻿﻿﻿﻿﻿﻿﻿﻿ https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics
5. ## dynamic theory

Your language is good enough for us to communicate about dynamic of motorcycles, my English is not much better. According to Newton, everything that has some speed wants to move on a straight line by itself and must be forced to turn. The forces of steering (wheels pointing in different directions) and friction between tires and pavement are the only things that force a car, truck or a motorcycle to turn, not the lean of the bike. A motorcycle can be leaned and still move on a straight trajectory if both tires are kept perfectly aligned forward. We only lean the bike to create a balance of forces between gravity and centrifugal effect and that balance is kept during the turn regardless of how much the rider hangs off. The more you lean a bike, the less misalignment both tires must have to keep the same circular trajectory and the front contact patch moves away from the rear one, which means less steering is needed (although the difference may not be noticeable). One of the reasons is that the distance at which the axis lines of both tires intersect each other must increase as the bike is leaned in order to keep the same horizontal radius of the curve. Please, take a look at these schematics and text in Italian: http://www.dynamotion.it/eng/dinamoto/8_on-line_papers/Pneumatici/Pneumatici_ita.htm
6. ## Throttle with brakes on

The main advantage I see is pre-loading the rear sprocket, chain and rear suspension while the chassis is still pitching nose down due to deceleration. The rear suspension remains more or less extended during the transition, rather than returning to normal after prior getting extended again under power. The top leg of the chain is slacking while braking and the transition to power always has a shaking effect, plus some dead rotation of the sprocket (if some play exists between the rear sprocket and rubber connectors to the wheel). That transition used to be less abrupt for carburated bikes than it is for the ones equipped with fuel injection (there is a time lapse after control input). For street riding, it is safe to use the rear brake for that purpose, rather than simultaneously manipulating the throttle and front brake controls in a fine manner.

8. ## How do you know you lean to the max?

Approximately 1.96 g. That magnitude would be approximately the result of multiplying the standard acceleration due to gravity (32.2 feet/second square) by the tangent of 63 degrees (1.96). That means that, depending on specific front-rear weight distribution, each contact patch would be feeling a lateral force (trying to make it slide over) which magnitude would be a little less than the combined static weight of bike, fluids and rider. That makes that rubber compund a fantastic sticky and resilient material. The IMU (Intertial Measurement Unit) in the MotoGP bike is made up of gyroscopes and accelerometers (usually a 6-axis system) that gather information on the bike’s chassis attitude. Because the previous research we did here (above picture), we can assume that with proper hang-off of the rider, the tire-width offset is compensated in such a way that the chassis lean angle is pretty close to the theorical dynamic lean angle (line of combined CG to centers of contact patches respect to vertical). The concept that I would like to present to new riders is that the magnitude of lean angle always follows the magnitude of those lateral forces, which we create by selecting the speed of cornering for a particular curve. In other words, although we surely can improve the chassis lean angle by hanging-off, we can't directly manipulate or choose the theorical dynamic lean angle of the bike, which is a natural balancing reaction (the CG-frame-tires aligns with the new resultant leaned force of cornering) and only depends on the square of the speed and on the radius of the trajectory we choose.
9. ## How do you know you lean to the max?

That is accurate, the frames (and suspensions) of motorcycles with tires of wide section will lean a few degrees more than the theorical lean angle shown in the graphic, which is the angle formed between a vertical line (the direction of gravity) and another line connecting the contact patches and the combined center of gravity of bike plus rider (please see first attached diagram of gravity and lateral forces). Hanging off reduces that difference, even eliminating it, as we discussed on these old threads: http://forums.superbikeschool.com/topic/3324-hanging-off-mathematically-quantified/?page=2 http://forums.superbikeschool.com/topic/3661-body-position-and-cog/ Note that in the case shown in that third picture-diagram of forces (Stoner's), the combined CG is relocated sideways enough to exactly compensate for the off-center relocation of the contact patch, reducing the actual lean angle of the suspensions and frame and increasing angular clearance.
10. ## How do you know you lean to the max?

I advise against that idea: friction would be the only thing preventing the bar from rotating around the fork's tube. It may be sufficient for normal riding, but it may suddenly rotate for high steering forces or head shakes or tank slappers. I would try finding the ideal position for the bars and still using a key to fix that position, perhaps drilling on the tripple or fabricating an offset kind of bridge that connects both original holes (clamp and tripple). Is the ideal position as shown in your picture?

13. ## timing of steering input and chassis attitude

I believe that the only reason for steering to be less accurate is a survival reaction of one hand fighting the other. That does not mean that we should reduce or eliminate the steering torque produced by one of the hands, but that we should observe that potential SR. Your bike my have a under-steering tendency, due to geometry or tires or tire's pressure. I would experiment with lowering the front end some and/or raising the rear end, in order to reduce the trail of the steering some. That would reduce the tendency of the steering to remain on a straight trajectory.
14. ## timing of steering input and chassis attitude

Basically, the same two processes happen simultaneously, only that in a shorter period of time than for a lazy turn. The front suspension and tire are loaded because deceleration, then that load caused by deceleration gradually yields as the load caused by the circular trajectory of quick-flick and tracing the curve rapidly increases (up to lower or similar value). You can find additional discussion about the quick-flick technique here: http://forums.superbikeschool.com/topic/4101-can-quick-turn-be-overdone/
15. ## Twitchy Throttle Response Hindering My Roll-On and My Confidence

If your in-line four is carbureted and your V-tween is fuel injected, you should feel the difference. Besides the above recommendations, you could remove any current rotational slack between rear wheel and sprocket. If everything fails, I would experiment by carefully using a little bit of clutch or rear brake simultaneously at the begining of rolling the throttle on (not by the book or desirable, but better that upsetting the chassis).
16. ## Consistent vs Accurate Lines

Excellent post, Hotfoot. ? It very well explains the "throttle should be open as soon as possible" line in the book. Prior reaching maximum lean or slidding state, the bike is always following the trajectory that the rider commands it to follow via steering and throttle. Good visual skills help me with the spatial awareness regarding where the bike is located at any time in a succession of turns and helps me decide about the proper moments to brake, accelerate and turn in.

18. ## Running off the road

Welcome, Don! Very true, as soon as we are not 100% mentally riding ahead of the bike, the perception (false or true) of excessive speed and lack of time and available space overwhelms our fears of not surviving the situation. "A superior pilot uses his superior judgement to avoid situations which require the use of his superior skills" - Frank Borman
19. ## 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
20. ## 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 weight 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 asymmetrical 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 weight 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 asymmetrical 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
21. ## 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
22. ## 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.
23. ## 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.
24. ## Can Weight Shift Theory be debunked?

In order to communicate with the same terms, are you refering to the rolling motion of the motorcycle? Is your question limited to the reactions of the bike and steering and trajectory following a lateral weight shift of the rider? Sorry, I couldn't clearly understand your question.
25. ## Experiments with Shifting Gears and Turn Radius

Because all the gears and sprockets that link the crankshaft with the rear wheel act like a lever: the rotational speed of the rear wheel gets reduced while its applicable torque increases. For the same degree of openning of the throtle, resisting load and rpm's, the engine generates certain amount of torque or rotational force. We have to work around that more or less constant amount of torque, playing with the gears, just like it happens with a bicycle. For a greater resistive load (going uphill, for example), we have to sacrifice rotational speed of the rear wheel in order to have greater torque there; hence, we switch to lower gears. One trick for riding in the rain is to corner using a taller than normal gear, which "weakens" the available torque of the rear wheel, which creates an extra safety margin regarding any mistake with excessive throttle that could overwhelm the marginal available traction. https://www.youtube.com/watch?v=3Tc3VIDQvh0
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