Lnewqban

1) The traction is so marginal that the front tire cannot force the bike to turn as easily as tires on asphalt can. Sometimes, the rider tries digging the front tire into the loose surface in order to gain a traction that depends more on surface material building up over the sides of the tire than on pure friction. He/she achieves that by transferring the weight forward, by moving the body forward in the saddle and by extending one leg forward. When the described above is not sufficient to turn the bike as quickly as the next racer can, he/she increases lean angle which makes the rear tire step out of line. That achieves two things: the torque on the rear tires pushes the front tire to stay more or less in track by sliding less out of the turn and the material building up on the out side of the tire helps improve its traction. 2) Making the most from the marginal available traction is the priority. Those are their racing lines. Outside-inside-outside lines are for reducing the length of the curve and increasing the radius when traction is plenty and surface is firm enough to grant a precise line.

In that hook is the main advantage of the quick-flick technique: a rider can achieve a few degrees of change of direction (horizontal) during the relatively safe transition from vertical to full lean angle. That lean angle will be less dramatic than the resulting lean angle (and cornering forces) of a lazy entering steering. In every turn, we must change the direction of the motorcycle. There is always an angle between in and out directions (45, 90, 120, 180, etc. horizontal degrees). The racer who can "rotate the nose" of the bike sweeping the full horizontal angle in less time, without crashing, has an advantage. An important limit to that rapid change of direction is available traction. According to Sir Issac Newton, any body in movement will follow a straight line, unless forced to change direction. Steering and available traction are all we have to force the bike to turn. The faster the turn, the stronger the cornering force (proportionally to the square of forward velocity). The tighter the turn, the stronger the contact patches need to grip the asphalt (inversely proportional to the radius of the circle described by the bike at each moment). The angle of lean at each moment is a very accurate reference for us to learn how intense is the cornering force that is trying to break that grip of the contact patches and to help the bike resume the straight trajectory (which is the natural thing, rather than turning). Since the quick-flick gains some bonus degrees of horizontal rotation for us and reduces the magnitude of the final lean angle some degrees (meaning less cornering forces), we can increase the speed around the corner in order to use that little reserve of traction. The quick steering uses the abundant traction of the vertical front tire and simultaneously rotates and flicks the bike certain amount of degrees. Regarding the line or trajectory, it means that we are transitioning from a straight line into a curve of constant radius as quickly as possible. A lazy entering steering is what we normally do in a car, because it takes some time to rotate the front wheels. What our car describes is closer to a parabola than to a semi-circle, it looks and feels like a decreasing radius turn. Please, see: https://en.m.wikipedia.org/wiki/Euler_spiral#Track_transition_curve https://en.m.wikipedia.org/wiki/Racing_line The lazy entering steering produces the same effect: less lean angle at the beginning, which trades off for a extreme lean angle (and cornering forces) around the apex (or tip of the parabola) where the radius of turn becomes very small. That extreme lean angle becomes your bottleneck, regarding speed and traction, even if you trail-brake all the way until there. Sooner or later you must rotate the nose of the bike around, quick-flick allows you to do it sooner (and safer) than later. Quick-flick goes very well with the late apex approach and allows a line that straightens the geometric curve very much. Using more width of the track when/where possible can increase your speed and improve your line of sight. The direction of the following turn is important when choosing a wide or narrow line out. Remember, on dry or wet pavement, the best and safest trajectory is that one that allows you to use the throttle golden rule. More discussion about that "hook" and quick-flick in wet conditions can be found here: http://forums.superbikeschool.com/topic/4101-can-quick-turn-be-overdone/

4. Your visor doesn't let you see as well. 5. The rubber of your tires is cooled down and the internal pressure decreases. 6. The feel of your brakes may change, as the temperature of discs and pads is never as high. 7. The feel of your hands and fingers is different under wet leather.

Carefully observe the hand and steering inputs of the rider in this vid, as well as how the rear tire reacts to those inputs (or lack of them). Keeping traction of front tire and torque flowing onto rear allows command of rear tire regarding returning to proper alignment. Just like needed for proper braking, the transfer of weight towards the rear should happen prior the contact patch receives the additional torque from the engine. The transfer takes some time and it can only be initiated by moderate throttle, which can be increased progressively as rear traction improves. That smooth initial throttle is hard to achieve in bikes with fuel injection and lacking traction control aid. https://m.youtube.com/watch?v=H93kPnDQEqA

Sorry to see that happening. It is hard to tell from that point of view and sound only. The engine can put a lot of torque on the rear wheel while in third gear. Could it be that inadvertently you applied excessive throttle, which made the tire break loose?

Because it is very complicated, the subject of friction between rolling rubber and pavement has been and will be debatable. It goes beyond the simple empirical determination of a coefficient between two sliding surfaces. Rubber is a material which properties change a lot under mechanical and thermal stresses. It acts like a viscous-elastic material and it suffers from elastic hysteresis. When the same area of rubber hits and partially slides over pavement, internal chock waves develop and the original softness of the rubber has less time to recover. It has been demonstrated that for stationary surfaces and for light pressures in the contact area between a tire and a road, the rubber will only make contact with about 5% of the road surface. As the contact pressure increases, the rubber gets squeezed into many of the smaller-sized cavities. The coefficient of friction is not constant for different conditions. Many universities have studies and papers explaining this. If interested, you can research "elastoplastic contact between randomly rough surfaces". https://en.wikipedia.org/wiki/Viscoelasticity https://en.wikipedia.org/wiki/Hysteresis#Elastic_hysteresis Nevertheless, let's assume that friction and area are more or less independent in this case. The useful range of traction of any tire depends on the pressure/temperature/stress over the contact patch. If that is true, then the rider needs to unload the front tire some, and overload the rear tire some, in proportion to the differences in the areas of both contact patches. If the rubber compound and manufacturer of both tires are the same, he/she wants to achieve the same pressure/temperature/stress on both contact patches while cornering. The whole idea of proper throttle control to achieve a proper weight distribution while cornering is based on that concept. "To determine an ideal scene for traction, machine-wise, we start by simply measuring the contact patches of the tires to discover what the basic distribution of loads should be while cornering. Roughly speaking, those measurements show that 40 percent of the total load should be up front, 60 percent at the rear.......... At the point where the correct transfer of weight is achieved by the rider (10 to 20 percent rearward) by using the throttle, any big changes in that weight distribution reduce available traction." - ATOTW-2

I believe that your above assumptions are correct, playersnoopy. While following any circular trajectory, what the rider feels on his body (against seat, tank, pegs and grips) is a force that is greater than his natural weight, which is nothing more than the vertical force resulting from the action of gravity (1 g) over his body mass. That additional force comes from the vectorial combination of natural acceleration (gravity) (Fg=mg) and centripetal acceleration (Fc=mV^2/r) over his/her body mass. The direction of that resultant force (Fr=square root[Fg^2+Fc^2])is more or less aligned with the lean angle because the contact patches are the only point of support and the bike must be in dynamic balance.Regarding maximum attainable tire's grip (to resist centripetal-induced-force), it should be proportional to the weight of the bike plus rider before they start moving and proportional also to the tires' contact patches. That weight is the mass of both combined with the vertical g, which oscillates around the magnitude of the natural gravity (g=32.2 ft/sec^2) while the bike rolls over the irregularities of the pavement. After a crest G<g (the bike+rider are moving down and weight less = less friction or traction on the contact patch to fight the lateral G). After a valley G>g (the bike+rider are moving up and weight more = more friction or traction on the contact patch).Some tires have a bigger contact patch as they lean. After several laps of a fast race, the rubber on the sides starts deteriorating, which may cancel the gain in area of the contact patch. I believe that the posts of this old thread will result interesting to you: http://forums.superbikeschool.com/index.php?/topic/3331-have-you-ever-slid-the-front-without/

I fully agree with you, faffi. Reason may be that it is easier to mimic performance riders "looks" than mastering other things that are less evident. Knee down seems to be the highest goal for many riders. Whoever feels the need to hang-off while street riding is speeding big time. What a pass at 11:15 of that vid! On his own words (copied from http://www.mikethebike.com/quotes.htm): The former editor of a magazine asked him: "What do you do to the others in order to beat them apart from outride them?" His response was: "Look at all of them on the front grid before the start. You can see it in their eyes. If they think they can beat you, smile, give a nod and a wink. It works every time. Then you go out and show them what you meant." Sadly, he died 35 years ago.

I believe that correct steering and hanging off are not related at all. It is more possible to introduce incorrect steering and throttle inputs while hanging the body off if not properly locked to the tank, seat and pegs. Going back to your first post: In the last century, we used to race without hanging off and that worked. I don't know about old bikes and riders being as fast as equivalent machines and racers of nowadays; it would be an interesting thing to watch if old conditions could be reproduced. How some things evolved: Engines went from light and explosive (2-stroke) to heavy and docile (4-stroke). Tires went from rigid/marginal grip (bias-ply) to pliable/super-grip (radial). Those two factors widen the profile of the tires, resulting in increased lean angles of the chassis for similar speeds and curves. At the same time, better surface of tracks and softer rubber compounds increased possible maximum grip, traction or coefficient of friction. Those two factors permitted harder cornering (more speed and tighter radius of turn), which resulted in extreme lean angles of the chassis of the bike (around 60 degrees). Bottom line: racing bikes can now lean beyond the dimensional limits of dragging parts. Hence, there is some room to increase speed around a turn if the chassis could be pushed away from the racer and a few degrees upright. Why to hang off for less dramatic and extreme corners if chassis parts are not dragging yet? Better suspension, which translates into more consistent traction, is the answer. The imperfections of the track induce vertical movements of the bike, but the strokes of the suspension are diagonal while the chassis is leaned (there is a useful stroke and a wasted one) and the combined forces of gravity and circular trajectory (some call it centrifugal, some centripetal, some g-forces) increase the load on the springs (as much as double the normal weight of bike and rider at 45-degree lean). Regarding the historical styles of hanging off: http://forums.superbikeschool.com/index.php?/topic/1362-knuckle-to-knee—dragging/

According to the headlines of this forum, we discuss "Anything that advances a rider's understanding of riding." As the background of all posters is not the same, we should try discussing complicated subjects in the most simple and yet understandable way. You are correct about the illusory nature of centrifugal force, as well as about the departure from the pureness of the academic discipline. Nevertheless, in my humble opinion, it is a simple shortcut to give the idea of the experienced tendency of the mass of bike and rider to resist the curvilinear movement of cornering. I believe that your explanation of the cornering force and having less friction when leaned is contradictory and inaccurate, as the cornering rider feels more than his/her static weight. Copied from: http://forums.superbikeschool.com/index.php?/topic/3723-the-1g-club/ "The barrier then is both physical sensation and visual orientation and I believe there is a make/break point in it. That point is 45 degrees of lean. At 45, the forces are a bit out of the ordinary. Along with the normal 1g down we now have a 1g lateral load as well. As a result the bike and our bodies experience an increase in weight. That’s not native to us and acts as a distraction and as a barrier." - Keith Code (2013) As you seem to be serious about the Physics of motorcycling and able to understand complicate explanations, I highly recommend you these two books: "Motorcycle Handling and Chassis Design: the art and science" by Tony Foale. "Motorcycle Dynamics (Second Edition)" by Vittore Cossalter.

. Imagine this diagram to represent the forces on the tires when cornering (weight and centrifugal), then rotating the picture 45 degrees counterclockwise. For Physics, the position of the bike (leaned or vertical) does not matter, only the magnitude and direction of the forces. It is just like the bike is straight up. Now, the rider weights one peg (standing directly above it). How the bike will react to keep the balance? It will lean away from the loaded peg, as much as needed to vertically align the compound CG (bike's and rider's) with the tires. It will do that with the help of the hands of the rider, who will instinctively hang from the bar (no steering perhaps) to keep balance.

That is an interesting question! You cannot do both things at once, just like you cannot stand on one foot while your CG if way off the vertical line going through your foot. You create pressure between tank and outside peg in order to have good traction in your outside foot, in order to lock your thigh over the seat in order to hang off the inside. Most of your weight is actually supported by your thigh and some by the inside foot, but again, the bike does not care about the way your weight is transferred to the contact patches of the tires. The important thing to note here is that, having only two wheels, the bike-rider assembly is always balanced (except when counter-steering), as much when leaned as when straight up. Balanced meaning that there are no forces acting to flip the bike out of that state of balance. When going on a straight line, the bike is balanced in a vertical position (when looking at it from the front) because gravity is pulling straight down and the CG and the points of contact of the tires must be vertically aligned. When going around a turn, the bike is balanced in diagonal position (leaned) because the resultant force of gravity plus centrifugal acceleration is pulling in a diagonal direction and harder than gravity alone. Because of that, you can experiment about alternating pressure on pegs and hanging off while the bike follows a straight line and you will have similar conditions than when cornering. Observe the reactions of the bike and the involuntary steering inputs (pressure of your hands on the bar) as you do so.

What is important is the location of your center of gravity respect to the bike. That center of gravity is located more or less close to your bellybutton and it is a theoretical point at which the addition of the weights of each part of your body can be considered concentrated at for any Physics calculation. Same applies to the center of gravity of the bike alone, including all the fluids, which is located more or less by the valves. Once your body is connected to the bike, regardless of the point(s) of contact, both CG's add up and relocate to a point between both individual GC's. For the bike to turn in a balanced manner (leaned over), that combined CG must be aligned with a line between both contact patches. Hanging off is moving the rider's CG towards the inside of the corner, which pushes the bike's CG towards the outside of the corner, achieving less lean angle for the chassis. More discussion on the subject:

The winning bike in the video is a modified monster Autorace machine; the oval track is Kawaguchi, Japan. Check this out: http://www.kawaguchiauto.jp/en/howto/performance This is the tire's profile of a Dunlop KR-73 installed in this bike: little resistance to rolling straight up and added surface when leaned over.

Those are two very good reasons! Bigger profile has more wall surface to transfer the heat into the surrounding air, bigger mass of contained air (harder to heat up and higher cushion capability), more rubber to wear within the contact patch and less pressure of contact (weight / area), which leads to lower temperature of the rubber. It is not only the power and torque during hard acceleration, but how frequently the rear tire is close to support the full weight of bike plus rider (close to wheelie). Not all is good regarding wider tires, since there is more unsprung weight, higher rotational inertia and bigger lean angles of the chassis. There are many reasons for the differences among those three types of bikes: it would be interesting repeating that race for a supermoto track and for a supersport track. Irregularities and traction of each surface, as well as layout of each track, make a big difference in machine design and performance riding.

As it is evident in this vid, it just can: it is possible if it is physically happening. All the contact patches of all the bikes were loaded by similar lateral forces, regardless lean angle, leaning of the rider, type or width of tires. Those lateral forces that tried to skid the tires only depend on the speed of the bikes and the radius of the turns, which were more or less similar for all those bikes. The forces that resist that skid depend solely on friction between rubber and track's surface. Why do you believe are the reasons for the particular conditions of that track (oval, flat, big-constant radius turns) favoring the specific type of bike that arrived first?

I would say do not. The general rule of throttle induces stability in pitch (remember the three axis of rotation crossing at the CG?), but this problem is in yaw. Comparing to aviation, this problem is very similar in nature to flutter of control surfaces: a rapidly oscillating mass fed by the energy of movement. Engineers design and test machines to operate at regimes far from resonance, in "normal" circumstances. As profile and softness of tires and rigidity of frames and telescopic forks have improved during the years, the problem is less common. Those are only two of the many factors at play, it still can happen to any normally stable motorcycle when some of the remaining factors get aligned in the wrong direction. Example: Worn bearings of swing-arm + tire hitting stone or road groove + specific speed of the bike. Copied from Chapter 11: "The less of a "whipping back and forth" mass you become, the quicker the bike will stabilize." You can read more about steering shaking, dampers, and wobbles in Chapter 8.

Many years ago, I had a motorcycle that loved doing that. I tried all possible tricks to stop the oscillation before becoming uncontrollable, being the most effective leaning the upper-body forward and clutching in. Braking was bad and accelerating was scary, although more effective: the problems are 1) the calipers/pistons are affected by the front shaking (to the point of reducing front brake power) and 2) to keep fine throttle input under those conditions. The causes are many, as well as the differences among bikes, but one good thing is not to remove the hands off the handlebar, especially while coasting or decelerating, with cross-wind or bad road surfaces or while carrying a heavy/bulky tail luggage. Bonus for your natural curiosity: https://en.wikipedia.org/wiki/Speed_wobble

Note that his left hand (and possibly the right one) was not on the handlebar at the very beginning of the vid. That allowed the steering to initiate a small oscillation, perhaps induced by the air turbulence of the truck and/or some wheel's unbalance and/or worn steering head's bearings. The tail luggage had the bigger lever to influence the steering and you can see how loose it becomes by the end of the fall. Note that his knees were not hugging the tank; hence, the loose masses of rider and luggage created a tip-of-a-whip effect, extending the oscillation's amplitude. The oscillations of the steering and bike increased because resonance: https://en.wikipedia.org/wiki/Resonance Skin and pavement don't mix

Are you fully conscious of your thought process and the conflicts that it brings while learning to corner? How difficult it is for you to keep a tranquil mind, eager to learn, free from old concepts, feelings and old fears? When you come to this school, you have been riding for a while. During that time, you have been accumulating experiences, techniques, advice (good and bad). Then, you are certain that you understand many things related to riding, speed, control and so on. You have developed a psychological comfort zone within which you ride. The school presents new things for you to learn now. Your experiences belong to the many days of riding, to the past. Do you see the conflict? Do you see the importance of reducing thought as much as possible, being thought that constant chatting, comparing, resisting, fearing, past memories, which can only slow your learning process down?

Gripping rubber.

The problem is that we are comparing things that are very different in nature: Steering geometry modification and throttle control. Steering geometry modification: Motorcycle steering has some built-in dynamic stability, just like the front wheels of a shopping cart. The front wheel steers around an axis that is always ahead of its point of contact with the pavement (distance that is named trail), which naturally straightens the steering up to follow a straight line, especially when the tire is disturbed by a road bump. Bigger trail makes the bike harder to deviate from a straight line, especially at high speeds, and vice-versa. Riders who prefer a lighter-quicker steering modify the geometry of the suspension in order to reduce that trail distance, while sacrificing some natural stability. When doing so by reducing the caster or rake angle in a few degrees, there is slight re-distribution of the weight over the tires, which is very small (about 5% of the total weight moves towards the front suspension for a reduction of rake angle of 3 degrees). Throttle control: By opening your throttle more or less, you have the dynamic ability of loading the front suspension and the smaller front contact patch with any weight magnitude between 0% and 50% of the total weight of the bike and rider, which makes a big difference respect to the fixed weight transfer discussed above (5%). Even more, by accelerating and braking hard you are simultaneously modifying the pitch attitude of the frame and that rake angle, and consequently making the steering heavier (accelerating: tail down-nose up) or lighter (barking: nose down-tail up). When you are turning at a fast rate and with a lot of lean angle, what of the two following extreme situations will keep your tires farther from a possible slide and crash: on the front brake or on the gas? And why? Chapter #3 explains the link between throttle control, suspension and traction. The rules of throttle control not only put the proper percentage of weight on the front tire, but put the front suspension to work in the more beneficial range and keep the pitch and height of the chassis as it should for stability and ground clearance.

If the engine does not stall, its torque tries to move the machine along the only degree of freedom that it has in that situation: vertically up. As both suspensions gives some, the frame goes high a little under torque and it goes down back to original repose height when the torque ceases. I like discussing this with you, Jay, as well as posting in a simple manner about things that are complicated, with the hope that it will help other riders that will read this thread in the future. Do you agree or disagree with the ideas of our previous posts? Doesn't the concept of some time needed for the transfer of weight to be complete for full braking capability work for your original post?

There is no more weight transfer once the bike does a wheelie or a stoppie: it is 100% of the total weight on the tire in contact with the surface; no more, no less. The wheelie and the stoppie are beyond the transient state of initiating braking that we are discussing. That is the state during which the bike pivots around its center of mass or axis of pitch (just like a seesaw or teeter-totter), progressively pressing more on the front suspension and front tire (which is the reason for which the nose dives and the tail rises up simultaneously). This link explains it better than I could: https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics#Braking_according_to_ground_conditions Again, with good rubber and on dry track, you can get away with suddenly stabbing the brake lever: the weight transfer will happen during the time dictated by the rotational inertia, but it will not make a difference, the contact patch will fiercely grip. Doing the same on public dirty greasy roads, right after start raining, will lock the tire and you will go down very quickly, unless you are quicker releasing that pressure on the lever: that is the whole point behind bikes equipped with ABS brakes. With no ABS brakes, you may be surprised of how hard you can brake in those conditions if you apply increasing pressure on the front brake lever in proportion to the rate of weight transfer.