| Author | Message | ||
     Blake |
repeat... Here's an experiment that might teach you something. With your bike supported by a rear wheel stand, sit on it in normal riding position. Now, without changing position or forward lean or anything else, quickly pick your left hand up off the grip. What happens? The handlebars turn hard left. Why? Because you were pushing on the right grip. Case closed. | ||
| M1combat |
Would you care to state any of your scientific bodies that explain this any differently than I do? Einstein says that a body in straight line motion tends to stay that way. If we move the contact patch to the right, the bike rolls about it's roll center in an anticlockwise fashion (viewed from the rear)... leaning to the left. We then are in a left hand corner... Thus it is explainable w/o shadow of a doubt that we turn right first to go around a left hand turn. Go down a road about 35 mph. Give the bars a slight but strong jerk to the right... Through the seat, you will feel the top of the bike go to the left. You can push or pull, just notice that the seat goes the opposite direction  . | ||
| Blake |
Not sure the seat goes opposite the tires. Might want to rethink that. The term "roll center" describes the axis around which the bike seems to rotate absent any lateral translation. But there may exist significant lateral translation to consider as far as what the seat is doing relative to its original track going down the road. It would depend greatly on the dynamics of the turn. Are you confused yet? | ||
| Court |
Einstein says that a body in straight line motion tends to stay that way. Uh....that might have been Sir Issac Newton. | ||
| Xb9er |
repeat... Here's an experiment that might teach you something. With your bike supported by a rear wheel stand, sit on it in normal riding position. Now, without changing position or forward lean or anything else, quickly pick your left hand up off the grip. What happens? The handlebars turn hard left. Why? Because you were pushing on the right grip. Case closed. Case reopened. What is your definition of a "normal riding position"? Lean forward using your abdominal muscles to support your upper body with some help from the gas tank or air intake cover on XB's. If you feel the need, put your toes on the pegs and squeeze the bike between your knees for more support. Adjust your upper body so that your forearms are parallel to where horizontal would be (if the bike wasn't on the rear stand) and elbows shoulder width apart. The longer your arms, the less you have to lean your upper body forward. If my instructions were good enough, you should now be in a position where you can grasp the grips in a neutral position, where your hands/wrists aren't supporting the weight of your upper body. Your arms and hands can be completely relaxed and you can push, pull, wave, do whatever with your hands. Now, following Blake's experiment, "quickly pick your left hand up off the grip. What happens?" Absolutely nothing will happen to the handlebars. This position is what I strive for when riding because it is comfortable, relieves pressure from shoulders and wrists, eliminates numbness of fingers from high frequency vibrations of the bars, makes it easy to control the bike, and it gives me the feeling of "being one" with my XB9R. It does not yet come to me naturally. I have to make a conscious effort and any increase in my stress level may cause me to lift my upper body, straighten my arms, push forward on the grips, etc. Isn't this discussion fun??? Mike. | ||
| M1combat |
"Not sure the seat goes opposite the tires. Might want to rethink that. The term "roll center" describes the axis around which the bike seems to rotate absent any lateral translation. But there may exist significant lateral translation to consider as far as what the seat is doing relative to its original track going down the road. It would depend greatly on the dynamics of the turn. Are you confused yet?" I understand roll center... If you apply force to one end of an object, it will rotate around it's roll center. In our case it's real close to the combined CG. In our case it's below the seat. You move the tires to the right abruptly and the seat moves abruptly (albeit a good deal less) to the left. Try it... Jerk the bars a little to whichever direction you like (prepare to recover) and the seat will move the other direction. This may be more evident on a bike with a very low CG, but I think will hold true on just about any bike. As far as lateral translation... Understood. I'm not sure that if you lazily roll the bike into a corner that it would go opposite first, but when snapped into a corner, it will, or at least it will be much more apparent. So yes, it depends on the dynamics of a corner. For the most part through this thread I have been coming from the "spirited riding" corner , where you would do something more along the lines of dropping a bike in a corner quickly as opposed to a lazy roll... "Uh....that might have been Sir Issac Newton. " Uh... Yeah . Thank you for the correction . I don't know what made me think Einstein... | ||
| Biknut |
einstein can speak for himself. he posts on this sight all the time. | ||
| Henrik |
have an understanding of what my arms are doing with the handlebars. Good point, me too It helps to have an understanding of how a motorcycles geometry works, and I do have that. Well gosh darn, me too ... In addition to decent insight into MC geometry, I have no doubt my expertise in anatomy and biomechanics at least matches, heck, might even exceed yours  Henrik, I pretty much disagree with everything in your last post. So when you dispute what I describe about my body position (obvious in the picture) and what type of input I make/am able to make to the bars and how ... well, then that makes it impossible to discuss  Henrik | ||
| Henrik |
Putting forward names like [edit] Tony Foale to support your beliefs is one thing, but show me where they've conclusively proved the points we've talked over her Credentials; don't know if anyone took the time to look around Tony Foale's site. If so you may have stumbled upon this. During some 40 years of practical and theoretical experience with both racing cars and racing motorcycles, Mr. Foale has built several experimental motorcycles to research and identify the fundamentals of steering geometry, and have developed the mathematical models for motorcycle handling based on these experiments. He currently makes a living as a consultant specializing in MC chassis and suspension design, "with particular interests in the development of computer simulation models predicting motorcycle behaviour". In short he's the guy that developed the modern foundation for how bikes are built these days - handling wise. So while the articles on his site may not contain the references to his original work, his 1984 book “Motorcycle Handling & Chassis Design” does contain the details. I have no doubt, that he has "conclusively proven his point." I guess it's possible, that Tony Foale through the last 40 years has managed to "trick" all of the motorcycle industry - but I must say, I doubt it  Henrik | ||
| Steve_a |
To begin a left-hand turn quickly, the tires must track right initially. (It is possible to enter very slowly by just letting the bike slowly fall to the left.) This has been measured a long time ago. (I've been trying to find my copy of the 1973 paper by Watanabe, which had some beautiful graphs, but it's gone missing). The interesting thing in Watanabe's testing was that the more and the quicker the tires track opposite at turn initiation, the faster the rider went through a S-turn. It's also absolutely true that the front tire is turned to the left when you're traveling steady-state around a left corner. Counter-steering is about getting the bike to roll to the attitude you want for cornering (or not). Steady state, the front wheel is roughly perpendicular to a line drawn to the center of the corner, that is, turned in. Another way of saying this is that the axle points to the center of the corner. Here's a chart of the torques and turning movements for a righthand corner from Vittore Cossalter's "Motorcycle Dynamics" book. Cossalter is a professor of applied mechanics at the University of Padova, and his speciality is motorcycle dynamics. Padova is the only university that has a graduate program in motorcycle dynamics and engineering, and Cossalter has consulted with both the Ducati and Aprilia race teams. Note that the turn begins in the top graph with steering torque and angle to the left. The second and third graph show there's an initial left acceleration and even a leftward movement of the bike center of gravity before it begins to go right.  (Message edited by steve_a on October 26, 2004) (Message edited by steve_a on October 26, 2004) | ||
| Mr_grumpy |
Mrs Einstein was with her husband being shown round a spanking new very expensive observatory, She asked what it was all for, & was told that it was to work out how the universe is constructed. Her reply was "that's a lot of money, my Albert does it on the back of an envelope" Draw your own conclusions as to my point  | ||
| M1combat |
Great info Steve A... I'll trust you didn't doctor those graphs . | ||
| Blake |
Donald (M1), Please rethink your assumptions. As the center of mass (CM) moves closer to the road the bike becomes more difficult to get leaned. Imagine the extreme, the CM coincident with the road surface. Lateral force generated by turning the wheel would then have zero lean inducing effect. Please also consider the anti-lean effect of the gyroscopic action of the wheels and engine. At elevated speeds it becomes more and more difficult to get a bike to lean quickly into a turn. The lazy roll will tend to move the seat opposite to the turn of the wheel, but as much due to gravity as anything. Consider a bike not moving at all. Stand it up and let go. It will rotate, but not about its roll center. The theory that there exists one specific roll center axis about which a motorcycle will always appear to rotate when leaned is fallacious, gravitational force and gyroscopic effects render it so. | ||
| M1combat |
"The theory that there exists one specific roll center axis about which a motorcycle will always appear to rotate when leaned is fallacious, gravitational force and gyroscopic effects render it so." Understood... The lower the CM (sorry for using CG before ) the smaller the lever that the tire patch's input would have on the mass. The CM would act "like" an unfixed fulcrum yes? I understand that (or I think I do ) the upper portion of the bike isn't "fixed" to anything whereas the lower portion is "fixed" to the ground via the tires so the bias would be that the lower portion would move more when the CM is at 1/2 the height of the bike... The roll center would generally be above the CM, but is probably dependent upon how much force is being applied at the tire patch. We have a certain amount of lateral force acting at the tire patch, but we only have inertia up top. I guess my point was that the roll center of the bike will be above the CM and below the top of the bike . I didn't attemp to fix the roll center to a location, but just say that it will roll about it's roll center. The location of which is dependent upon many factors. In any case, it seems to be that with my XB when I give the bars a good jolt to the right, the seat pulls my posterior to the left abruptly, but less distance than the tires moved to the right, indicating that the bike is indeed rolling about an axis that is above the pavement and below the seat. I didn't intend to say that the roll center is fixed, it migrates, just like it does with a car. The proper term being "Roll Center Migration". With a car, it tends to migrate left and right, whereas on a bike, I believe it migrates up and down. Please correct me if I'm wrong . P.S. Does a bike have anything comparable to the FVIC or SVIC on a car? I would imagine that if it does, it would be the relationship of the swingarm angle to the rake angle and the length of the swingarm, and the arc the axle travels through. Just curious... Also... When making decisions about geometry... Would you use the swingarm pivot point and the axle to determine the angle, or would you draw a line perpendicular to that angle from the axle to the edge of the tire and use the angle from that point to the swingarm pivot point? Just curious... | ||
| Biknut |
dou, my heads starting to spin? | ||
| Mr_grumpy |
If you take a longditudinal line from the flange sprocket to the fetlockstrongler valve & bisect it with a line between the front spindle & rear widget you will have a point exactly at the equilibrial centre, depending on mass of rider & riding position. If you then take into account tyre pressure & suspension preload, you must then add the weight of what you had for dinner & multiply by the sponge coefficient. To find the ideal turning point you must start from a perfect scenario, then adjust using visual & physical inputs utilising all sensory receptors. The lean angle calculation must be made by starting from a basic, that is upright, angle of 90° and subtracting the fat angle. To be strictly accurate the speed must be exactly registered & adjusted for pie. The pie must be well cooked & served with mash, peas, & gravy. Doing this repeatedly will expand your roll centre, thus providing an expanded rider/machine interface. Hope this clears up any confusion. | ||
| Rocketman |
Blake, yaw torque has by far the greatest effect on a motorcycles steering. Your last post is misleading in this respect, as you continue to harp on incorrectly about CM, and the gyroscopic effect being somewhat overriding when it is not. The lateral displacement of the CM (oh we've got to go all technical now with abbreviations??) will cause big differences in steering but will not make it any harder to get leaned in. The above graphs posted by an authority on the matter show no more than the result of initiating counter steer to the handlebars. That is NOT the purpose of this conversation! I too am well aware of the teachings at the University of Padova, and I would be mindful not to misrepresent them. Rocket | ||
| Reepicheep |
If the gyroscopic force does not become a huge factor at speeds, how come my bike falls over when it stops, but stays upright when I am moving? How come I can whip the right to left full lean to full lean transitions easily at 15mph on a battletrax course, but have to really wrench the bars to get even half lean and shoot across a couple lanes on the interstate at 70 mph? | ||
| Newfie_buell |
Because the gyroscopic effect is greater at higher speeds. If not the bike would flop over. Nothing worse than a floppy bike!!!! | ||
| Mr_grumpy |
Yeah, my wife hates a floppy ride too, | ||
| Rocketman |
If the gyroscopic force does not become a huge factor at speeds, how come my bike falls over when it stops, but stays upright when I am moving? The gyroscopic forces caused by the spinning action of the wheels has virtually nothing to do with keeping the bike upright in forward motion. If they did, you'd probably never get a solid wheeled Fat Boy to turn. Try balancing your bike off the ground midships on something like an upright tyre, or two, placed in line with the bikes own wheels. I assure you if you spin both bike wheels as fast as you please your bike will fall over. Better still, put your bike on rollers and run it up as fast as you like. Without a rider present it will fall over. How come I can whip the right to left full lean to full lean transitions easily at 15mph on a battletrax course, but have to really wrench the bars to get even half lean and shoot across a couple lanes on the interstate at 70 mph? Speed, time and distance! Please, no more stupid questions otherwise we'll need a proper expert Bill. Rocket (Message edited by rocketman on October 27, 2004) | ||
| Buells Rule! (Dyna in disguise) |
The gyroscopic forces caused by the spinning action of the wheels has virtually nothing to do with keeping the bike upright in forward motion. If they did, you'd probably never get a solid wheeled Fat Boy to turn. Incorrect. | ||
| Reepicheep |
There are no stupid questions Rocket, just stupid people So, if I took the back wheel off your Duc, put a solid bar about two feet long through the axle, and spun the tire up to roughly 70mph... how fast do you think you could rotate said wheel 90 degrees? How much power do you suppose you would be imparting to make that happen? This is the force you are dismissing as insignificant. I won't say it is the primary factor determining motorcycle dynamics, but I also won't dismiss it as insignificant at speed. I have never, and will never, profess to be an expert in the matter. If gyroscopic forces are not significant, then given equal forces applied to the bars, the *time* required to transition from full right lean to full left lean should get shorter, or at least remain unchanged, as I go faster, right? Is that what you experience? | ||
| Crusty |
This poor horse died weeks ago. Why keep beating it? | ||
| Biknut |
if you consider the angle of the dangle, and then factor in the heat of the meat minus the square of the hair, you're probably fixin to fall down anyway. | ||
| M1combat |
Because it's a very good topic Crusty... It has good potential. | ||
| Buells Rule! (Dyna in disguise) |
Potential yes..but like the political & war threads it doesnt appear that some folks views are being changed at all. Thats fine, if folks want to continue to think like prehistoric cavemen & refuse to evolve with the times, who cares? I do believe at 1 time a lot of people thought the world was flat & they could prove it...now we know it was Rockets ancient relatives who believed that silly notion. | ||
| Crusty |
There are still a lot of people who believe the earth is flat. I just found the website of the International Flat Earth Society. All I can say is holy ••••! There's no accounting for what some people will believe. | ||
| Buells Rule! (Dyna in disguise) |
Rockets name wasnt on the list was it?? | ||
| Rocketman |
Bill, of course it will be hard to turn a wheel spinning at 70 mph in my arms with a 2ft bar shoved through its middle. What happens when one applies forward motion to that same spinning wheel? Hey, like magic it gets easier to turn. So, did the bike running on the rollers with no rider to balance it, stay upright? Nope, it fell over. Dyna, your R1 sums up your tastes perfectly. I mean, how could one learn anything from riding such a machine? You know they softened out the R1 for 04, for wussies like you. Stick around and you might learn something, but somehow I doubt it. Rocket |
