Jump to content

Lnewqban

Members
  • Content count

    262
  • Joined

  • Last visited

  • Days Won

    5

Lnewqban last won the day on July 13

Lnewqban had the most liked content!

Community Reputation

12 Good

About Lnewqban

Profile Information

  • Gender
    Male

Previous Fields

  • Have you attended a California Superbike School school?
    No
  1. Wet Vs Dry riding

    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.
  2. What happened- My Highside Crash

    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
  3. What happened- My Highside Crash

    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?
  4. Lowering the body

    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
  5. Lowering the body

    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/
  6. Against the flow

    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.
  7. Against the flow

    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/
  8. Lowering the body

    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.
  9. Lowering the body

    . 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.
  10. Lowering the body

    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.
  11. Lowering the body

    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:
  12. Seems you do not need wide radials

    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.
  13. Seems you do not need wide radials

    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.
  14. Seems you do not need wide radials

    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?
  15. Over 1m views- what caused this crash?

    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.
×