| Author | Message | ||
     Dynarider |
Speaking of tankslappers. How is a high-speed tankslapper possible if steering is sooo hard at high speed? ================================================== I know it cant be because the front end is too light or any of that bullshit. I experienced my 1 & only major tank slapper 3 months ago on my Dyna. Coming out of a slight curve, hit some tar snakes & the front end washed out a bit, saved it but as soon as the front regained traction it went into a violent slapper & I fought it & almost won, but in the end myself & the wife both ended up getting spit off at about 50mph. Tank slappers=very scary shit | ||
| Blake |
James, Thanks for voicing your concurrence. Jim, "So I guess Tony rewrote his book to be in agreement with what you say, and he is now as right as you are. Glad we got that cleared up. " Jim, I don't imagine that Mr. Foale wrote his new book in order to agree with me or my views. I am encouraged that in his new book Mr. Foale corrects prior egregiously erroneous assertions that were extended as scientific fact. Thanks for reposting the links. I'm not big on email lists. Too much email, usually. I prefer the web page forums. ![:]](http://www.badweatherbikers.com/buell/clipart/proud.gif) I think I will go ahead and send Mr. Foale an email expressing my views on the presentation of his "gyro only" simulation results. "There is no such thing as centrifugal force." That may mislead those unfamiliar with the concept. The link you post (outstanding site btw  ) covers the concept quite well in physical terms. In semi-plane English, centrifugal force is an "apparent" or "perceived" force resulting from an acceleration of an accepted frame of reference, specifically it is the force perceived as one orbits or circles and where the acceleration is the centripetal acceleration, the progenitor of the real force that acts to maintain a circular path of travel. For example, when we ride in a car and travel in a circle we perceive that we are being pushed outwardly away from the center of the circle, where actually we and the car are being pushed inwards in order to maintain its circular path of travel. We dub that perceived force the "centrifugal" force. It is just like if we were sitting in the bed of a pickup truck when the driver accelerates aggressively from a stop; we might perceive that there is a significant force pushing us rearwards towards the tailgate. In fact the only "real" force is the acceleration force that is pushing forwards to speed up the truck and the people riding in it. If the tailgate were lowered and the bed covered with ice, we would simply slide out the back of the truck. We would not accelerate; we would not even move; absolutely no force acted upon us. It is only because our minds accept the truck as a frame of reference that we perceive ourselves being forced out the back when in fact it was the truck that was forced forward. Centrifugal force is kinda like an imaginary friend; it exists within the context of certain frames of reference when we perceive it to exist; we just know that it isn't real. I hope that makes some sense. | ||
| M2me |
Oh my God! I'm having flashbacks to my high school physics class! Did I really trigger all this with an offhand remark about hanging off the high side in a slow speed turn? But seriously, it has been very interesting reading so far. This has been a very educational and, at times, entertaining thread. Hey, anybody wanna go smoke a doobie? Oops, sorry I thought I was still back in my high school physics class.  | ||
| Richieg150 |
Ya,what he said!LOL | ||
| Blake |
Greg, Glad you are still here. It is unfortunate however that your contributions have drifted more towards heckling than meaningful debate. I guess that was premature, you have posed an excellent question... "How is a high-speed tankslapper possible if steering is sooo hard at high speed?" Firstly, ever try to stop a high speed tank slapper. It is pretty much impossible without a functioning steering damper. Why? A tank slapper is the manifestation of an undamped run-away harmonic oscillation. Do you understand the incredible power of undamped structural/mechanical harmonics? The gyro effect plays a significant role along with the steering geometry, inertial properties of the front wheel, loading of the tire, as well as the stiffness of the tire, wheel, and its supporting structure (forks and steering head). As I've said before with respect to steering, the gyroscopic effects are secondary to the effects of the steering geometry and the related interaction of the front tire with asphalt. You should understand that what is difficult for a man to move quickly is no big deal to a run away harmonic oscillation and that the leverage and forces that can be exerted by a 550 lb mass moving at high speed are far and away in excess of any meager forces a rider might impart to the handlebars. Do you agree? Actually, your question further solidifies the truth about the role of gyroscopic precession in the control of motorcycles. Consider the following and tell me where I'm wrong. If gyroscopic precession were, as you contend, the primary mechanism responsible for causing a motorcycle to lean and change course, then a tank slapper could never happen at high speed. If gyroscopic precession were so significant on our motorcycles, as you seem to believe, then every time the front wheel oscillated from one side to the other, through a considerable angle, the bike would be violently tossed over from one side to the other. We both know that doesn't happen. Why? Because gyroscopic precession of a motorcycle's wheels is in no significant measure capable of forcing a motorcycle into quickly leaning over and/or changing course. Next question please.  | ||
| Aesquire |
Dyna, The reason the 10 speed bicycle rides well hands off is steering geometry. Rake and trail affect stability more than gyro force on a light wheeled bike. I have a steep (74deg head angle) race bicycle that does not do at all well hands off, while my mountain bike (72deg) cruises around fine H.O. I've had light & heavy wheels on both bikes, and gyro forces ARE a factor, heavy wheels are more stabilizing, and do increase steering effort. If you measure the geometry of Motorcycle, scooter, 10 speed, etc. you will see the compromises made in each to balance stability vs. handling. Itty bitty wheels are easily upset by road irregularities (see Razor scooter injury web sites lol) due to angle of attack on obstacle AND have less gyro stabilizing force. | ||
| S320002 |
Blake, 'Simple physics is just that. It is full of frictionless bearings, volumeless masses and formulas which ignore higher order effects.' "A gyroscope is a pretty basic mechanism, a spinning disk; gyroscopic dynamics are perfectly understood." But the dynamics of motorcycle steering is neither basic nor easily understood. "The physical relationships describing the behavior of a spinning gyro are infinitely simpler than those needed to describe the flight of a bumble bee." Ah, but the physics of motorcycle steering is much more complex than the behavior of a spinning gyro. Just as the flight of a bumble bee is much more than the flapping of wings. "(Blake, you left out the word Simple. An effort to discredit or misdirect?) Physics is full of formulas which ignore higher order effects? Please name two." If you go back to the Physics Site YOU recomended: 1. The mass of pulleys. 2. The friction of bearings. While I think this is a very good site to help someone understand basic physics, it certainly falls short of making one a mechanical engineer. "Formulas do not ignore higher order effects; people do." A fact which you have made abundantly clear. Perhaps you didn't realize that in addition to angular momentum there is a significant component of linear momentum in the front wheel to consider at high speed. This is one of the reasons that large steering inputs are not practical. And yes I know you have mentioned linear momentum. What it seems you have not done is to consider the interaction between the two. You have made several sarcastic remarks to the effect that I don't believe in the laws of physics. Once again I look at this as an effort to misdirect or discredit the truth of my statements. If you were indeed an engineer you know that I would need to know and use the laws of physics to be successful in that profession. While I do not, and will not, post a lot of formulas and diagrams that does not diminish the truth of what I have to say. Greg | ||
| Aesquire |
Oh, yeah, great thread! I have had long arguments with bike & moto riders about counter steering. I believe it exists. They don't. to quote a pal "why not just lean?" sputter sputter. | ||
| Jima4media |
Yeah, this is a great thread. The tank slapper part of it reminded me of an incident in Safeway. My shopping cart hit a piece of gravel, and the front wheel went into a violent cart slapper. It is those damn small wheels with no mass, and not enough speed to give you any magic gyro action, I say. If I hadn't had that 20 pound bag of kitty litter up front, I might have high-sided that sucker. I jumped on the back and leaned as hard as I could to the inside of the skid. There was a loud applause from several soccer moms that witnessed the whole thing. ;-) | ||
| Dynarider |
Posted by Blake...the leverage and forces that can be exerted by a 550 lb mass moving at high speed are far and away in excess of any meager forces a rider might impart to the handlebars ================================================== OMG you could say that again. My arms & shoulders hurt for a month after I tried wrestling with the tank slapper my bike gave me. Suprised it didnt rip my arms off. | ||
| Blake |
Aesquire, I think we all agree on the countersteering thing, Greg is just unclear about the mechanism responsible for it. Greg, "But the dynamics of motorcycle steering is neither basic nor easily understood." It ain't rocket science. The bike leans to permit gravity to balance centripetal acceleration commencing upon turning into the curve and following a radius dictated by the attitude of the front wheel. Gyroscopic effects are negligible to the overall scenario of turning a motorcycle; they simply hinder the ease of the action as speeds increase. However the gyroscopic behavior of each wheel and the engine are perfectly understood and can be easily incorporated into a dynamics model. It is actually pretty damn simple. You have three axes of rotation, the steering head, and each axle. Each is separated by reasonably fixed constraints and simply definable geometry. A few simple coordinate transformations from the fixed frame of the bike yields a simple relationship between front wheel track and rear wheel track and even the centers of the contact patches. Appropriate constraints and boundary conditions would be defined within the coordinate system defined at each contact patch... lateral constraints are per reasonable coefficients of friction, and of course vertical translational constraints. Gravity applied via negative acceleration in global Z direction. Initial velocity specified. Simplifying assumptions: Action of suspension is neglected, no acceleration or braking is considered, aerodynamic drag is neglected, rider is constrained to motorcycle in all degrees of freedom. Apply mass and inertia properties. Define a simple steering input control loop relationship. Let it fly. Wait, someone has already done that. Did you see the copy of Mr. Foale's graph in yesterday's archive?  "If you go back to the Physics Site YOU recomended: 1. The mass of pulleys. 2. The friction of bearings." Can you please show me the formulas and indicate what higher order effects are ignored? "While I think this is a very good site to help someone understand basic physics, it certainly falls short of making one a mechanical engineer."  I don't follow your point. "Perhaps you didn't realize that in addition to angular momentum there is a significant component of linear momentum in the front wheel to consider at high speed. This is one of the reasons that large steering inputs are not practical. And yes I know you have mentioned linear momentum. What it seems you have not done is to consider the interaction between the two." I admit, I did not know there existed any significant interaction between linear and angular momentum. I'd be obliged if you could explain that to me. "You have made several sarcastic remarks to the effect that I don't believe in the laws of physics." But Greg, you don't even accept the validity of a simple equation defining the behavior of gyroscopic precession. You poo poo a basic law of physics by invoking the supposed mystical complexity of motorcycle steering. WooOOOooo. :wary: What do you expect? Get real. There is nothing so complex or mysterious about the way a motorcycle steers. "Once again I look at this as an effort to misdirect or discredit the truth of my statements." Unfortunately the "truth" of your statements is hard to find. Here are some examples... "Gyroscopic forces are what allow high speed motorcycle maneuverability. Imagine you have leaned way over in the first part of a high speed chicane. How do you bring the bike upright so you can quickly lean in the opposite direction for the second part of the chicane? Why you take advantage of something called gyroscopic precession by counter steering of course." and "...the initial rotation of the bars to the left causes the front wheel to rotate slightly to the left around the rear wheel. As a result, gyroscopic precession forces cause the REAR and the front wheel to tilt to the right." and "What I do disagree with is (that) Gyroscopic forces and GYROSCOPIC PRECESSION are a great hindrance to high speed motorcycle maneuverability." Do you really want to continue go up against the likes of Sir Isaac Newton and Kevin Cameron on this issue? "If you were indeed an engineer you know that I would need to know and use the laws of physics to be successful in that profession." I disagree. I think a lot of "engineers" have forgotten their physics a long time ago. Education is not the same thing as practice. "While I do not, and will not, post a lot of formulas and diagrams that does not diminish the truth of what I have to say." "A lot of formulas and diagrams..."? How about providing just ONE in support of your contentions? Besides, I disagree. Failing to provide ANY concrete evidence or sound logic in support of your theory does indeed pretty much diminish the credibility of what you say. Get real Greg. Let go of the myth. Mr. Foale did, you can too. I know it hurts to have your closely held long standing beliefs exposed as an unwitting fraud; we're here for you compadré, we feel your pain. Repeat after me... That'd be "em equals phi-dot gamma-dot eye." | ||
| Blake |
Dyna, My old Yammer XZ550RJ, aka "The Nightmare" would with the slightest tap on the bars at around 38 mph go into a sustainable tank slapper. The front end was soft and I had the rear jacked up to max preload. Anyway, I too learned real quickly how ferocious that action can become. Freaked me out. | ||
| Rick_A |
I did a huge powerslide coming out of a turn today and spun the rear wheel while the front wheel was the air (been a little cold today...tires wouldn't bite)...and I thought of how nice it was having these heavy PM's and big flywheel to stabilize it  . | ||
| Lornce |
quoting blake: "I'm not sure what you are getting at. Once again, I am not saying that gyroscopic effects are not present within a motorcycle and its wheels. They most definitely are. My point, again, is that gyro effects hinder, rather than enhance, the ease with which a motorcycle at speed can be turned. That is it. Pretty simple. Funny how people react and get all off course in debating the issue" Blake, there's no doubt increased gyroscopic forces offer increased resistance to changes in direction. I've not implied otherwise. Lighter is better when you want spinning objects to alter their path. No argument. quoting blake further: "Lornce, You aren't suggesting that we should not comment or refute quoted material that is offered as fact when it instead is simply wrong or misleading, are you? I only refuted Mr. Foale's statements with regards to gyroscopic effects on motorcycle steering when they were set forth by others here as expert testimony." Never implied comment or refutation an unsound notion, simply raised the question of efficacy in Tony's absence. You should take your cape into the ring on the MC Chassis and Design list, and see what you have to offer. They embrace bold intellectual combatants. In all honesty, I haven't followed this thread closely enough to even know the minutiae of the dissagreements: don't have the time. But your personally insulting and chiding remarks aimed at Mr. Foale were rather unseemly and only served to undermine your credibility. That's primarily what I take issue with. If one is correct, and I make no claim to knowing who is, it's not necessary to denigrate an opponent to be validated. Simply make your points, answer questions clearly and in as simple a manner as possible, and let the facts speak for themselves. It could lead to more fruitful discourse: if that's what's desired.... regards, Lornce | ||
| Jima4media |
Thanks Lawrence, That is what I was getting at also, and you said it much better than I. Tony Foale was a racer, a bike designer, and engineer, and a writer who has written a couple of the best books available on the subject of motorcycle design. Blake, When you threw out arguements like "Bullshit!" and "Magic Gyro" you are losing credibility right off the bat. When you explain yourself fully as you have in some of your posts, you come across as much more knowledgeable. When you stated "Mr. Foale corrects prior egregiously erroneous assertions that were extended as scientific fact." you never stated what those assertions were. Jim | ||
| S320002 |
Blake, The front wheel and tire of a motorcycle does not simply spin like a gyroscope. It rolls (linear motion), turns about the steering axis, slides, moves up and down, changes shape and does several other things in the course of less than a second. The rear wheel and tire does many of the same things. In addition, because the wheels and tires are doing all of these things, the chassis is constantly changing geometry. The interaction and result of all these factors cannot be defined with a few simple equations. In fact it cannot be accurately described with a complex matrix of equations. Even computer simulations are not completely accurate. If they were then there would be no need to spend months test riding prototypes of new motorcycles. It also means that there would be no need to test chassis set ups and tires prior to a race. "It ain't rocket science." No it's chassis science. If it were as easy a you claim, the perfect motorcycle chassis would have been designed years ago. Does the perfect motorcycle chassis indeed exist? If not, do you think you could design it? Lornce makes some very good points. I have not tried to follow all of your twists and turns and turnarounds either. Some times ago I made the statement that a gyroscope does indeed become more stable as speed increases. I'm sure you remember that but have chosen to ignore it. What I didn't, and still don't, agree with is you statement that it makes steering at high speed "sooo" difficult. Sorry Blake but I am beginning to find your retorts boring and insulting rather than challenging. Greg | ||
| Steve_A |
Hmmm . . . this is one long thread. But a few points are still worth making. Counter-steering produces both the effect of steering the wheel out from under the c of g, causing the bike to lean in the opposite direction, thus setting a motorcycle up for a turn, and a gyroscopic precession that also makes the motorcycle lean in the opposite direction. Neither effect is insignificant at speed. Note long-distance wheelie specialists who equip their machines with a small electric motor to keep the front wheel spinning, and thus allow steering via precesssion forces with the front wheel in the air. Second, motorcycle dynamics are extremely complicated. I know the head of tire design at Metzeler (a German PhD) once wrote a model with 50 non-linear equations before giving up for a while. However, simpler models predict trends, and there is a tremendous amount published on the subject -- including the thesis of one of the engineers at Buell, who wrote a force-based model to make it a bit more intuitive. Third, tank slappers can be a problem. Dyna's seems to be a classic, with a sliding tire and rippled pavement while leaned putting a very large input into the front "frame" (the mass and structure on the front side of the steering head)to produce a wobble. A steering damper might have helped. What also might have helped would have been not to have fought it. True wobbles are so high-frequency that a rider can't stay ahead of them, and trying to exert tight control on the handlebar at that time is almost more likely to make the problem worse rather than better. In general, riding with a light touch on the handlebar except when a change of direction is desired helps to decouple the rider from bike oscillations, and they'll generally damp more quickly that way. (A different but telling example of this is the wide bars on early S1s -- people who rode with a light touch loved the leverage, while people who rode "tight" ended up inputting weaves into what was otherwise a very stable machine.) Finally, Erik Buell does not much like steering dampers, because they always in part mask steering feel. He'd much rather produce machines that are inherently well-damped for wobble so a damper is not required. | ||
| Jima4media |
Steve, Was that Buell engineer Abraham Askenazi who co-wrote Building Better Products with Finite Element Analysis? As stable as Buells are, especially the newer XB9's, all the race team seem to use steering dampers anyway. But then again, the take off the ZTL perimeter brake and replace it with dual discs up front, change to a chain drive instead of belt, replace the top end of the motor, and add a fairing, too. Anything for better performance in a race, right? Jim | ||
| Steve_A |
>>Was that Buell engineer Abraham Askenazi who co-wrote Building Better Products with Finite Element Analysis? << Yes | ||
| Davegess |
A question that comes to my simple mind... Does the lightness of the XB front wheel coupled witht he extra weight at the rim because of the brake make the biek more stable at speed and contibute to the heavy sterring some writers talk about? i.e. is the front wheel a more effctive gyro 'cause there is a greater percentage of mass at the rim of the wheel? | ||
| S320002 |
Dave, Concentrating the mass near the outer perimeter of a gyro increases gyro effects. Therefore the lighter tire would decrease the effect but the rim brake would increase the effect. Greg | ||
| Jprovo |
Dave, I don't think so, having heavier (than the XB) spokes or two big rotors (like most sportbikes do) should have similar (maybe more) inertia (gyroscopic effect) than the XB wheel/ztl braking setup. I think that the low cg of the XB series is what makes it feel more heavy steering. I think that the higher the cg a bike has, the more tippy or easier steering it is going to feel. James | ||
| Dynarider |
Steve, I thought the same thing about ahving a light touch on the bars but the bike got so violent the ass end was actually trying to come around & meet the front. A million things are going thru your head at the time & the one big thought is.....This is going to F@ucking hurt!! For someone to actually be able to ride it out, they either have to be real damn lucky, or maybe have experienced it so many times that its 2nd nature. I think for 99% of us normal riders we are going down when it happens. | ||
| Rick_A |
Finally someone puts that info up there short, simply, and succinctly. Thanks Steve. I had a tank slapper once landing a crossed up wheelie out of a turn. I held on loosely (or rather the force did that for me!) and I imagine the steering damper helped much as it was quickly quelled. Buell builds some inherently stable machines...but the damper can aid in the rare out of the ordinary oscillation. I think that the low cg of the XB series is what makes it feel more heavy steering. I think that the higher the cg a bike has, the more tippy or easier steering it is going to feel The low CG certainly contributes...but the ZTL rotor has to affect the actual steering effort at the bars more. Steel weighs a lot more than aluminum...so the spoke weight is less a factor. In the Pro Thunder machines the magnesium wheel actually weighs less than the stock Buell XB unit. The dual disks are closer to the hub than the ZTL setup, so it'd be interesting to know what the actual difference in handling is. The higher CG bike is easier to lean in but harder to right/transition. | ||
| Steve_A |
Hi Dyna -- What you're describing with the ass end wanting to come around isn't what in the technical literature is known as a "wobble", which is a front only oscillation. It's a "weave", and specifically a cornering weave, a coupled oscillation of the front and rear frames, the bike pitching, rolling, and yawing all at the same time. In your case, the loss of front end traction and the bumps set it off. Weaves are typically lower frequency than wobbles (1 1/2 to 3 hz compared to 8 to 10 for wobbles). Your situation is one where greater frame stiffness might actually have helped a lot, as well as really good performing rear shocks. A steering damper almost certainly would not have helped; in general, by increasing the coupling between the front and rear frames, a steering damper makes weaves worse, while being very effective at damping wobbles -- which these days are most commonly seen accelerating out of a bumpy corner hard while leaned well over. I've had a few full lock wobbles in my riding career, and have ridden a number of bikes that corner weave pretty dramatically -- the first Suzuki Intruder comes to mind. But a situation like you're describing with a sudden large-amplitude weave with a passenger aboard isn't one I'd want to encounter. You'd need a good amount of luck to come out of it, and the start of that luck would probably come from not trying to fight the bike. Dirt riding in sand washes or mud would be good practice, but a little hard to pre-plan for this unusual emergency. | ||
| Dynarider |
Ive got some pretty decent progressive shocks on the rear of the bike. Over 52,000 miles & never had anything like that happen with this bike before. Bikes always been real composed & has handled all I threw at it. Even done 1 track day on it & a couple battletrax events & never a problem. This was definately enough to put the fear of god in me. | ||
| Dynarider |
BTW, I have experienced some minor tank slappers or whatever they would be called when accelerating pretty damn hard on the X1 & the front end is slightly bouncing off the ground. The bars have a couple times started to take off & I just nailed the gas a little harder, brought the front end up into a nice wheelie & then everything fixed itself. May not ne the correct approach, but it worked.  | ||
| S320002 |
I don't know if it's on film anywhere but the most awesome tank slapper I ever saw saved was by Miguel Duhamel. He was coming out of turn three at Laguna Seca while leading the a Superbike race (1998 I think). All of a sudden he looked like he was riding a seriously bad ass bull. It was too fast too tell how many cycles he went through but he saved it and won the race. Greg | ||
| Blake |
Lornce, "But your personally insulting and chiding remarks aimed at Mr. Foale were rather unseemly and only served to undermine your credibility." Please help me out and show me where I directed any personal insults towards Mr. Foale. Jim, "When you threw out arguements like "Bullshit!" and "Magic Gyro" you are losing credibility right off the bat. When you explain yourself fully as you have in some of your posts, you come across as much more knowledgeable." Point taken. Would "Bullpoo" be any better?  "you never stated what those assertions were." I quoted and commented on his assertions in another thread, I previously included a link to that very post herein. To reiterate, Tony Foale *had* originally asserted that, gyroscopic forces were primarily responsible for turning a bike at speed, namely that.... "...the actual counter-steering movement is very small, since gyroscopic precession depends for its strength on the speed of movement not on the amount of movement. Even his comment about gyroscopic precession was misleading. It would have had us believe that rate of handlebar actuation is more important that the force of actuation in overcoming the gyroscopic effect. Not true, as the governing equation clearly shows. Greg, We all understand that the front wheel both rotates about multiple axes, and translates as it rolls down the road. Please explain to me, however, as you asserted earlier, the interaction that exists between linear and angular momentum. Never mind, I'll save you the trouble. There is none. The two are completely in inexorably separate, 100% independent of one another. As far as the complexities of chassis and suspension behavior. I agree; that is a complex system to simulate along with the dynamics of rider, bike, and aerodynamics. But Greg, we are not talking about chassis behavior or trying to exactly replicate real world behavior of a motorcycle in every exacting detail. Rather, we are talking about the basic mechanism(s) through which a motorcycle and its rider execute a turn. An infinitely stiff chassis and rigid (no) suspension do not change the basic mechanism through which a motorcycle turns, so in considering the topic, we can ignore any chassis flexure, and suspension motion. Do you agree? Besides, what is a "complex matrix of equations"? If you are referring to finite element analysis, I think you meant "vast matrices of variables"; the equations are actually fairly simple and there are relatively few. I'm amused by your wild extrapolations. I'm not asserting or even hinting that the analytical model I outlined would facilitate the creation of the "perfect motorcycle chassis", nope, not at all. In fact it had nothing at all to do with the chassis other than the basic geometric relationship between the steering head and wheels. Please try to stay focused man. Neither, as you assert, have I conducted a debate fraught with "twists and turns and turnarounds." That would be like talking about chassis design and simulation of the entire detailed real world behavior of a motorcycle, when instead we are debating only the mechanism responsible for causing a motorcycle to turn.  "What I didn't, and still don't, agree with is you statement that it makes steering at high speed "sooo" difficult." So you still disagree with, not only the personal experience of me and countless others, but also the laws of physics? Got my new issue of Cycle World today. It's kinda like Christmas comes once a month. Anyway, Kevin Cameron has an excellent article in which he dissects the evolution of Moto GP racing machines. Here's an interesting quote germane to this discussion:
What he is basically saying is that in order to tolerate for the duration of a race, the extreme amounts of heat generated by heavier machines being run at extreme cornering speeds, front tires, like their counterparts at the rear, would need simply to become larger. Why don't they? Because a larger front tire, though more able to absorb and dissipate heat, would significantly increase high speed steering effort thus hindering more than helping overall cornering performance. In other words, bigger tires would exacerbate the gyroscopic effect and make steering more difficult and slower. "Sorry Blake but I am beginning to find your retorts boring and insulting rather than challenging." Sorry to hear that. I'll leave you alone. For a while anyway while I pick on Steve_A and JProvo. | ||
| Blake |
Steve, Way cool of you to join the discussion. Just finished reading your CW piece on the prospects of a street version of the RC211V. I agree, it is only a matter of time. On gyro effects... How much applied moment, whether through precessional or inertial origins, does it take to maintain delicate balance while wheelying versus snapping a racebike into a 60o bank at 100+ mph? I wish I had access to Buell's mass/inertial properties data. Dave, What Greg said. In addition, it is important to understand that the gyroscopic strength of any rotating mass is proportional to its effective radius squared (r2) (The inertia (I) term in the equation that I keep posting includes the r2 term). So even though the Buell's front disk is large, it's effects on gyroscopic effect are not as severe as one might guess. Kinda makes you wonder if the XB9's special lighter front tire was specified primarily to improve suspension efficiency. If you are interested, the equation for "I" for a disk is simply 1/2mr2 where m is the mass and r the radius of the disk. For an annular disk we just subtract the missing inner portion so we get 1/2m(ro2-ri2) Where "o" and "i" subscripts indicate outer and inner radii, respectively. |
