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Lnewqban

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Lnewqban last won the day on April 1

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  1. 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
  2. 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
  3. 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
  4. 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.
  5. It could be off some degree. As far as I understand it, the lean angle shown in the display of a MotoGP is calculated based on the rate of leaning over speed from a vertical, using radial acceleration data supplied by the IMU. Because the inertial reference of the bike changes when cornering, there is no way for the blind (it has no horizon visual reference) IMU to directly "feel" and measure lean angle. Any blindfolded passenger of that bike would be lost about angle as well, his/her only clue about the intensity of cornering and resulting lean would be the sensation of increased body weight. The only accurate way to calculate the lateral acceleration and resulting force is by accurately knowing both speed and radius of the trajectory. I understand that chassis lean angle is the most evident clue that we normally have to guess how much stress we are putting on the contact patches, but the above graphic of lateral g-acceleration versus angle of lean shows us that strees-angle relation is not linear. What amazed me about this remarkable article written by Keith ten years ago was the fact he exposed (opening my eyes to this phenomena) about the needed finesse required when approaching maximum lean angle due to the rapid increase on dynamic forces, loads and stresses: "The barriers then are both physical sensation and visual orientation, and I believe there is a make-or-break point. That point is 45 degrees of lean. At 45 degrees, the forces are a bit out of the ordinary. Along with the normal 1g down, we now also have a 1g lateral load. As a result, the bike and our bodies experience an increase in weight. That's not native to us, and acts as both a distraction and a barrier. Once we become comfortable with 45 degrees and attempt to go beyond that, the process begins to reverse. Immediately we have more lateral load than vertical load, and things begin to heat up. Riders apparently have difficulty organizing this. Suddenly, we are thrust into a sideways world where the forces escalate rapidly. While it takes 45 degrees to achieve 1g lateral, it takes only 15 degrees more to experience nearly double that (depending on rider position and tire size)." https://www.motorcyclistonline.com/leaning-bike-code-break
  6. 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.
  7. 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.
  8. While riding on the mountains you should not be pushing your tires to the limit; that just means excess of danger with little reward or improvement of skills. Please, note that I mention the limit of physical pavement-rubber traction and not lean angle of the chassis. Lean angle is a natural consequence of the centripetal forces of turning and it mainly depends on the square of the speed of the bike and on the inverse of the radius of the turn: meaning in simpler terms that double the entry speed (but same radius) puts four times more lateral stress on the contact patches of the tires and that half the radius of turn (but same speed) puts double stress on those patches. The manufacturer of your sport bike tries to provide a lean clearance that matches the maximum traction capability of your tires in good pavement conditions. The resulting angle of lean must be there to compensate for those cornering lateral forces in such a way that the bike keeps its lateral balance (not crashing over towards the outside of the turn). What is happening at the same time? Both tires "feel" an increased weight of your body and the bike, as much as double (2g) around 60-degree lean; hence their sections become less pliable and have to work harder to keep grip. The suspension is now compressed by the added weight and its work to follow the surface and keep the rubber in contact with it is more difficult because the direction of the strokes is inclined while the irregularities of the track keep pushing it vertically. All the above works as described if, and only if, you have the luxury of clean dry pavement. Otherwise, your tires will have less capacity to resist the action of those lateral forces (assuming good conditions of tires, inflation and suspension, as well as good riding techniques and per-tire-weight distribution). How much less traction will you have? That is something impossible to predict on public roads, where you could suddenly find spills of oil, Diesel, anti-freezing coolant, or sand or street markings or steel manholes or animal carcasses. If you ride on the edge of available traction, you will not have available traction to use in the event of an emergency or evasive maneuver, like braking or swerving. You always choose entry speed to negotiate certain radius of a fixed corner, lean angle follows that decision adjusting itself to keep balance, and both tires and suspensions are loaded with extra forces, which should never grow beyond the limits of traction for the specific conditions of the road. Please, read some more about this: https://www.motorcyclistonline.com/riding-tips-traction-science-tires-keith-code-break https://www.motorcyclistonline.com/blogs/tread-envy-code-break https://www.motorcyclistonline.com/blogs/dragging-your-knees-code-break https://www.motorcyclistonline.com/leaning-bike-code-break http://forums.superbikeschool.com/topic/3331-have-you-ever-slid-the-front-without/
  9. 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?
  10. About your #2 question: Your priority for street riding should be safety, which has more to do with high alertness, with good judgement of entry speed, with understanding of traffic situations and with proficient visual skills. Your body position should be such that it serves as a good base for those things, it should be comfortable, it should keep you in total control of the machine. The extreme body positions that you see in track practices and races are not really necessary if you ride within or not much above legal speed limits. The lean angles and cornering forces on your tires should be moderate, so you will always have a safety margin or reserve to use in unexpected road hazards or traffic emergencies. You can experiment with leaning only your torso and head into the turn or even hang off your hips some, finding your most comfortable and safe body position. I would avoid dragging knees on public streets, but would know how to increase leaning angle and assertively swerve as emergency maneuvers.
  11. 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.
  12. 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/
  13. 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).
  14. 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.
  15. It could be that you are not following two fundamental rules of cornering: 1) Looking deep into the turn: You can only know that your trajectory is one foot off if you are looking close in front of your bike. 2) One steering for the whole turn: You may be adjusting your steering along the turn in order to achieve your goal trajectory. Think of the unintended consequences that you are creating if you are doing so, like diversion of attention, disorientation, over-stressing the front tire, etc. The way I visualize cornering trajectory: to me it is like shooting a ball into the basketball hood from a distance, you feel the cross-wind, you estimate the distance and the angle, you gut-calculate the whole flight of the ball and then you impart your best directed push hoping for the best. Sometimes you miss for little and sometimes you nail it. The hard mental, visual and calculation work in cornering happens prior the turn-in point, which is equivalent to the moment of actually pushing the ball. Let the bike "fly" describing that natural arc, free of unnecessary minute steering inputs and lean angle adjustments. Missing an apex for 12 inches may add a few feet to the corner's total trajectory, which is not a big difference for a bike that moves 88 feet per second (60 mph). Distracting your attention from proper throttle control and from reference points and from spatial location may slow your bike much more.
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