racer

Good luck!

Ok...my last post was late at night after a long day and I was not clear in my descriptions. For the sake of clarity... In the third paragraph when I said, "rotate the arm up", I meant pivoting up around the rear axle. When I spoke about the chain tension fighting rotation at the pivot point, I meant the swingarm pivot point assuming a roller topped by the chain in the "parallel" configuration. This roller position has no basis in reality, just what my mind pictured. The ATK system that Keith mentioned would not seem to be quite like this. I can't find a picture of this system, but, from Keith's description, it sounds like the rollers would need to be above and below. Without seeing the set up I can only imagine. But Keith said that the torque force was greatly reduced... not eliminated. If the swingarm pivot is changed to be neutral at sag with rider, there would seem to be a progressive increase of torquing chain force directly proportional to the amount of swingarm deflection (in either direction) under acceleration. So, being that upward torque is not desirable, some position locating that neutral position should be near (or in the extreme above) the top of suspension travel (in case of hitting a big bump under accel), thereby making the amount of downward torque somewhat adustable. Anyway, the super-conducting electro-magnetic rear hub drive would seem to be the only absolute model for elimination of any chain force torquing the swingarm and isolating the rotational force. I'm not sure how that relates to "horzontal force" at the moment. So, wheel radius/circumference (and perhaps sprocket) radius with applied chain force assuming level ground. Must be a formula for that. And the amount of "horizontal force" is going to be limited by the mass of the motorcycle and the lever it has for resisting the rotational force at the rear wheel. Hence the idea that keeping the front wheel on the ground is faster. This would also seem painfully obvious. I have no illusions that I am discovering anything here (except for myself). That's all the time I have. Thanks. Bill

Hey Tim, I'm not a mechanical engineer and I am simply trying to work through this complex problem in my head from memory without so much as a motorcycle sitting in front of me. As I alluded to in my original reply, I hadn't really finished thinking through the whole thing yet. And as much as I enjoy the game of trying to do that without referring to any other materials or asking for help, it does lead me to some half baked ideas based on faulty assumptions from time to time. And being relatively certain about most of what I talk about, it is also easy to fall into a 'habit' of speaking from a position of certainty. I try to remember to stay on top of that. That said, it was not really my intention to end our discussion, I simplynot sure I have really worked through it all yet and don't want to misspeak myself or confuse other people or devolve into an argument without basis as it were. I'm happy to be wrong. I just like to see if I can figure stuff out. And, in this case, it may be too much for someone lacking a complete education on the matter, no matter how sharp I am. And what I wanted to work out was the counter-steering thing I have been trying to work out on and off for about 8-9 months here. Oh well. I guess it's gonna have to wait a little longer. lol. That said, I was in the same place you are about this rear geometry thing half way through my original reply yesterday and did some ear steaming brain effort on it. And went around in several circles from several angles. And mostly decided to stick with what I knew for sure, which is the rotational force applied to the wheel. Which obviously tries to rotate the arm up. And the thought that it is this that tries to lift the arm as opposed to pull it down. And that the lever for that is quite small, namely the radius of the rear sprocket. (This is all with a parallel chain) And also that chain tension is going to fight the rotation at the pivot point against the mass of the bike pushing down. Even in and perhaps especially in a wheelie. And I had the thought that in a wheelie, varying the acceleration and tension might reduce that effect at the pivot. With chain force applied completely to the sprocket, the chain won't provide any linear force to the swingarm. I don't know if that means there is none, I simply worked from the premise that, at the very least, there is much less as was demonstrated from Keith's experiment with Eddie and tried to develop a theory to fit a possibly incomplete data set. That said, I believe that a horizontal component of force must probably be considered with some upward angle of force. And I am still working out how to sort that out. I have a gut feeling that a composite force vector might be correctly drawn from the contact patch to the CG or there abouts. And perhaps this is separate from the rotational force at the wheel which might be why the bike can wheelie and not slow down? The truth is gut insitnct and intuition commonly don't line up with the reality of complex physics like this...so, I'm gonna leave it at that. Tell me what you think, and I'm going to read up some material about wheels and angular momentum and such and how that getsw reduced to a singel force vector in this scenario...eh? Some if not much of what I have found on so called "motorcycle" sites is nearly laughable. And I feel like I'm cheating if I peek. My personal game. And perhpas inappropriate for this site? I don't know. But there it is. I'm off to bed. Good night. Bill

Hey Tim, I believe your static test is still using the chain to act on the swingarm. I think it is essentially the same example as the prior wall test except you apply force with the wall instead of the engine. At the moment, the only way I can think of to actually remove the chain from the equation while maintaining the component of acceleration is to make the chain parallel to the swingarm, which has been done and tested. Earlier I referred to a post by Keith Code in which he discusses these tests conducted with World Champion Eddie Lawson riding the bike. The relevant post is the last one in the thread titled "Weight transfers...Does the back really go up?" I originally found it by using the search function for the word "squat". In any case folks, Like I said in my first reply to MotoGB, the significant fact for a rider is that the swingarm does go down and the suspension does get "harder" under acceleration. Cheers all, Racer

hey tim, i think your static test is still demonstrating chain pull.

oops, hey tim, you were posting while i was editing. i need to go take care of something. i'll try to be back shortly. in the meantime, check out the edited post. tell me what you think of the new examples. cheers

Hey Tim, Only when the chain pulls at an angle to the swingarm. Respectfully, I think that rotation of the rear wheel and horizontal motion or force are irrelevant to the swingarm going down under acceleration. It is in fact the chain pulling down on the swingarm and shortening the wheel base that allows the rear wheel to claw under the bike, not the other way around. This is clearly demonstrated by orienting the chain pull parallel to the swingarm and observing no rise. Under acceleration, the friction or resistance (which could be considered horizontal) at the rear contact patch allows the chain to pull down on the swingarm. The wall is a convenient way of isolating the relevant action with "infinite" resistance or "infinite" acceleration. But I think it might create the impression of that horizontal force being the actor. Think of the bike rollin along at even throttle at about 30 mph. Now add some gas. Does it still feel like horizontal force is pushing the swingarm down? Hypothetically speaking, if we removed the engine and chain-drive entirely and installed a super-conducting electro-magnetic drive system inside the hub of the rear wheel, thereby eliminating all chain forces, perhaps a down angled swingarm would be affected by "horizontal force" at the rear wheel. But I suspect it would be more proper to say that rotational forces at the hub attempt to rotate the arm up and around the axle and are resisted by the mass of all the batteries replacing the engine...and, again, it would seem that the arm rotation allows the wheel to move horizontally inward, not vice-versa. Damn. I tried. Cheers, Racer

Hey Tim, We seem to be on the same page regarding squat vs rise. However, I don't quite agree with your description of the why. Even though I am far from an expert in physics, I will try my best to explain and illustrate what I think are the mechanics of it. In a nutshell, the driving force is the chain, and the resistance force is the contact patch. When considering movement of the swingarm due to acceleration, the amount of resistance to rotation at the rear contact patch acts like an anchor point. If you make a line drawing with two lines, one for the swingarm and another line drawn from the contact patch to the axle, the chain pulls forward and down on the middle (axle) due to the offset of the chain from the swingarm. Linear force is applied by the chain at an included angle (inside the angle of the two lines) at the end of the swingarm to the degree that the rear wheel provides resistance. If the bike were suspended off the ground the swingarm would still pull down under acceleration. The effect would be most observable in first gear from a dead stop. The mass/stationary inertia of the rear wheel would provide some resistance for the linear offset chain to pull against in direct proportion to the mass of the rear wheel (or mass distribution of the rear wheel for physics experts). The more massive the wheel, the more effect the chain would have on the swingarm under acceleration. Back on the ground, the mass of the rest of the bike on the contact patch provides major resistance for an even more effective anchor point, so to speak, allowing the offset chain to pull still more on the swingarm at an angle. If I simply pinned the chain to the end of the swingarm it would do the same thing. Due to resistance at the rear wheel, the chain is being variably pinned to the swingarm under acceleration. The chain force is divided between rotating the wheel and what "spills over" or is released through swingarm rotation or deflection. The more acceleration, the more resistance, the more swingarm deflection. As the wheel spools up, the resistance drops and the chain force on the swingarm declines. So that covers the normal bike with an offset chain. In the parallel chain scenario: If the chain is parallel to the swingarm rather than offset, the force/reaction will be entirely rotational at the rear wheel (axle) with no offset linear component from chain pull. And, technically, the bike is now more efficient. Hang the bike back up in the air. Will the resistance of the mass of the wheel still provide an anchor for the chain to pull the swingarm down? No. There is no offset. Back on the ground, the entire chain force is applied parallel to the swingarm at the top tooth of the sprocket to rotate the wheel or rotate the swingarm and bike up and around the axle. (Wheelie.) The radius of the sprocket is a lever for the drive force of the chain. The radius of the wheel is a lever for resistance. With the front end (up against the wall) held down and back with infinite resistance, and without the offset angle of the chain acting on the end of the swingarm, the length of the lever for the chain force to act becomes the RADIUS OF THE SPROCKET (approximately three inches) for a force acting parallel to the swingarm attempting to either rotate the wheel or rotate the swingarm and the entire bloody bike up around the axle (wheelie). (As opposed to the chain force acting on a lever the length of the swingarm pulling DOWN against the shock while up against the wall.) In this scenario of a parallel chain up against the wall, the rotational force applied to the three inch lever of the sproket would break the chain, break the sprocket or spin the tire before creating lift in the rear. Only by the pivot coming up could the swingarm go down, and in that case, the chain is no longer parallel to the swingarm and it is again an offset linear component. phew I will edit for clarity and brevity. I know there is much redundancy and wordiness. Especially in the second half. But, I think it is essentially coherent if not cohesive enough for now. I am sure there is a chapter somewhere in Twist of the Wrist (if not a single paragraph) that spells it out better. Cheers, Racer

LOL@ trumpy I'm sure I have NO idea what you mean, haha.

I have met a few racers who believe that keeping the tire constantly on the warmers will prevent degradation from heat cycling. The best source for that information is probably your tire manufacturer. In any case, it only takes about one and one half laps to warm a tire. Crashing due to cold tires is a matter of self-control, not inevitability. And generally speaking, based on about ten years of corner-working experience, I can say that the vast majority of crashes are not due to cold tires.

Hey jrfuisz, If the front wheel was skidding, wouldn't there be hundreds and thousands of little skid marks on the pavement at the turn in point of a corner? I might be pushing a tad, but, in any case, I think the friction at the contact patch is an anchor for leaning the bike. The "bicycle wheel" experiment you refer to demonstrates something called "gyroscopic precession". Essentially, if one applies torque to the axis of a spinning body, mass or wheel, the axis will deflect at ninety degrees to the plane of rotation and applied torque. In plain english, when you steer right, the spinning wheel will lean left. Step one: Grab a bicycle wheel and spin it up and hold it in your hands by the axle. Step two: Move it around and have fun. You will notice that when you turn the wheel right, it leans left. If you turn the wheel left, it leans right. This is precession. The precessional force is significant. Consider the mass of a motorcycle wheel compared to a bicycle wheel, multiply by say 30 mph or more and you are talking orders of magnitude. Of course a motorcycle is more massive than a wheel and there is forward momentum and inertia and another gyroscope at the rear... I haven't been able to work it all out in my head yet. It may be too complex to do without some more study. As for your statement: "Your bike is turning because of the displacement of the CG relative to the bike's direction (more or less - a diagonal from the rear contact patch roughly 2/3rd up the front suspension.)" I'm not quite clear what that all means. But, I think the traction at the front wheel is important no matter where the leaning force comes from. Racer

Hey Alan, Excellent example! I was going to mention the dyno but didn't think that most folks had access to one or even the experience of ever having seen one in action to be able to relate to it. But yes, that is a perfect example and since the forks are already tied down it further isolates the action by removing the forward force against the wall as a variable that might lead to confusion. You should have bet your mates a little sponsorship money. Anyway, aren't you supposed to be at the track? Or is that next week? Cheers, Bill PS: My "theory" as it stands needs serious editing IMO. It boils down to the chain not being parallel to the swingarm. And it isn't really MY theory. Just an observation... made before by others like Keith Code.

Hey dja1, I don't know if the 70 series tire will fit under your fender. However, I can tell you one way to get an idea. The aspet ratio is width over height expressed as a percentage of height. In other words, 120mm wide and 70% of that width tall. 5% of 120mm is about 6mm or 1/4". Measure the clearance under your fender and to see if it will accomodate another 6mm or 1/4". You should also consider the wear of the current tire. Look at the tread depth to get an idea of what you need to add. That said, often times the measurements on tires are not exactly accurate. I do adjust my geometry when using different size tires, but, I measure the tire itself and adjust accordingly. Racer

Hey guys, Higher and wider bars will provide more leverage. For a 250 GP bike my question is how much leverage do you really need? That said... aerodynamic drag is important for racing. Get behind that bubble. The first CSS classes I attended 20 years ago replaced the Ninja clip-ons entirely with Storz superbike bars. They looked and felt like dirtbike bars, but BOY did they make a big difference. However, the fairings were also removed and the key word was "school". Not "racing". While comfort is good and discomfort a distraction, there is a certain amount of reconditioning or training of one's body involved in learning to be competitive in any physical sport. That said, I always adjust the levers for a comfortable straight wrist and ease of operation. I think the positioning of handlebars tends to be mostly a personal choice. I moved the handlebars on my streetbikes below the triple tree/yolk when converting them to race setup (along with many other mods). By contrast, I didn't need to do too much to my factory roadracers. And yes it was DAMN uncomfortable the first time I squeezed onto a 125. Honestly, the first time I sat on a 250 felt like moving into first class on an airplane. So I have to giggle a bit about the "contortions" of squeezing onto a 250, but, I get it. It is a big change from a 600. In any case, the cut in the bodywork will give a good idea of what will work or what is standard. See where other people put their handlebars. If you are tall and your elbows hit your knees then perhaps moving them up will help you stay behind the bubble. You can always change it back. @ jps600rr I have never seen a bike with the throttle side set higher and can't think of a reason why it might be a good thing to do. It sounds uncomfortable to me at best. So I can't speak to why the bikes you saw were set up that way. Were they race bikes? Were they pro's? My advice would be to ask the owners why they did it. And to consider the source of any info you get. Gotta run. Good luck.

Hey jr, I think I found by searching under "squat". There's a thread about rear rise that ends with a post by Keith about Eddie Lawson trying a set of chain rollers (sorta like they put on dirt bikes I think) to attempt to limit the effect of the chain pull making the suspension harder under acceleration. Eddie didn't like it and preferred not to use it. However, I believe that the stiffer suspension is due to the chain applying a force that resists compression at the rear shock.

OK...if you search the word squat on the forum, it results in a thread titled "weight transfer...does the rear really go up?" In that thread, the last post is by Keith and he relates the story of Eddie Lawson and the chain rollers and almost verbatim what I said just above. Good kid that Keith. Taught him everything he knows...

Hey Tim, Specifically, it is the drive chain force being offset to the swing arm. A picture is worth a thousand words. Sit down on the ground next your (or any) bike and look at the angle of the top of the chain compared to the swingarm. They aren't parallel. With the pivot acting as a fulcrum, the chain applies angular moment to the swingarm. Being stationary against the wall effectively isolates this by removing weight transfer due to acceleration. Even if the forks compress while the bike is stationary, any forward weight transfer or "unloading" at the rear will be scientifically insignificant. Probably less than 1%. Well, that's getting better, eh? Pretty soon I'll be able to say it in one sentence of plain english. Racer Then again if the chain rides on top of a chain guide over the pivot...oh man I gotta go look at a bike. I'm starting to psych myself out...lol.

jrfuisz, Thanks for that infromation. I've never ridden a bike with TC or ABS or a telelever front end. I wouldn't choose traction control for myself. I do have one question about a statement you attribute to Sir Code. You said, "...he designed something to limit the effect the throttle had on compressing the suspension." Can you elaborate on what that was? And can you enlighten me about how the throttle compresses the suspension?

Hey killa, Even though it is only one second a lap, it is possible that your friend could be leaning over more due to differences in general riding style such as how much he hangs off or doesn't hang off, or how quick he flicks into a turn, etc. And, if you were on the same bike with the same tires at equal pressure, one second a lap would represent a relatively small difference in tire heat. But, we must consider the size/weight and power of the bike that will also contribute to wear characteristics. If you are riding a litre machine and your friend is on a middle weight bike, that too will make a difference. That said, though I am not familiar with the current specifics of all the tire brands/models, it has been my experience over the years that different brands DO generally have unique characteristics. So, it seems likely to me that a completely different brand of tire utilizing different construction and/or compound would exhibit some different wear characterisics. In any case, I think you have the right idea. Logically speaking, a stiffer suspension creates more stress at the tire. Good luck, Racer

Hey Killadude, There are too many unkown variables in your example upon which to base a singular conclusion. A harder tire compound or higher beginning tire pressure will result in a similar result as your friend's. Softer compound will exhibit more rubber wearing off. Lower tire pressures will result in more carcass flex leading to hotter temperatures and more tread wear. Also, if your friend is faster and using more lean angle he will be knocking the little rubber balls right off the edge of his tires. That being said... A stiffer suspension setting will put more stress on the tire. Not less. Cheers, Racer

Alan, Keith posted that same front wheel against the wall example on another thread here. It does isolate the relative action well. Maybe I can do a search for it and copy/paste it in. I can't comment on the words of commentators or ex-pro racers. However, the feeling of weight bias to the rear combined with the front getting light or "coming up" under acceleration could contribute to the perception of squat. The "up against the wall" example would remove it from the equation, which then begs the question of whether or not the rear weight bias under accel can overcome the angular moment created by the chain pull at the rear of the swingarm. My gut feeling is a big NO. Even a few hundred pounds of weight will be overcome by the horsepower being applied there. How much does a horse weigh? That said... With the front wheel against the wall, I think the rear would perceptibly rise to the naked eye. It is my opinion, finally, that the pertinent point is the effect on the rear suspension. Regardless of whether the rear appears to rise or not. Thank you very much for your kind words. I'd like to think I'd make a good coach anywhere. But, NZ is good. Thank you Keith for your years of dedication to sorting it all out and writing it all down. And providing a forum for relationships like this. Cheers, Bill

For anyone who cares, my last post of cobbledy-gook has been somewhat edited for clarity and brevity. Thank you for your patience during this time of personal difficulty.

Hey Alan, Quick "turn in" or "flick" allows a bike to use less lean angle for a given speed and corner. The longer it takes to get to max or final lean angle, the later a bike begins to actually carve the radius of a corner and the more lean angle will be required to complete an effectively tighter radius. A slow "turn in" deepens the effective turn point by the distance traveled while executing that slow motion "flick". This prevents the novice from realizing how much speed they could carry as they must use excessive lean angle to get through the rest of that corner which leads to premature dragging of bike parts and the perception of being "fast". The "quicker flicker" drags nothing on the same machine, at the same speed, in the same corner. As for the rear squat vs rise argument... (I am going to disregard tire growth under extreme acceleration as I feel it is a secondary issue.) While acceleration does transfer weight to the rear, the triangular relationship of the swingarm pivot to the rear axle and the angle of chain pull from the front sproket will determine what and how much effect acceleration will have at the rear suspension. From a side view, the drive chain applies forward force to the rear end of the swingarm which forms a lever with the fulcrum located at the swingarm pivot. Ideally, the swingarm pivot would form a straight or nearly straight line between the front sproket and rear axle (at sag with rider) to minimize affecting the rear suspension under acceleration. When the swingarm pivot is above a line drawn between the output shaft and rear axle, the forward force of the drive chain will also apply a downward force (angular moment referent to the pivot) to the swingarm (and try to extend the rear suspension) under acceleration. Whether or not the rear of the bike actually goes up or not, the downward force applied at the rear of the swingarm impedes compression of the shock. While (the bump in) the road is pushing up on the shock, the chain is pulling down on the shock, effectively making the rear suspension stiffer or harder. (This will also affect traction and tire wear.) (If the swingarm pivot were below the line between front and rear sprockets, the chain pull would try to compress the rear suspension and impede rebound.) All the motocycles I've ridden fall into the first non-ideal category of the rear getting harder (or attempting to rise) under acceleration. Kawasaki were experimenting with adjustable eccentric swingarm pivots on their superbikes to sort out the ideal geometry 10-15 years ago. I recall some talk of this "idealized" geometry research being incorporated on production sport bikes. Note: Trying to change the rear geometry with rear ride height or spring pre-load will affect the front geometry and the proper functioning of the rear shock. A last off-topic thought about swingarms and chains... The rear axle describes a vertical arc through the travel of the suspension which means that the rear axle will be at its furthest point from the countershaft when the rear suspension is compressed in line with the swingarm pivot and output shaft. It is best to adjust chain slack to accomodate this level of compression of the rear suspension. Or you could end up breaking your chain on the first lap of a 24 hour endurance race that you should have won... Of course, Keith Code has written extensively on these topics in his The Twist of the Wrist series as well as on this website. (And I am sure he could give you a simple yes or no straight answer to the question of squat vs rise. ) Cheers, Bill

Alan, I agree that TC represents a legitimate gain for safety, especially in slippery conditions and on larger and/or more powerful motorcycles. The same could probably be said for ABS in those same circumstances. And there will certainly be a market among the safety minded and those who desire every techno-wiz bell and whistle option. BMW is the perfect manufacturer to lead the way. I hesitate to refer to "Zen and the Art of MC Maintenance" here for the more philosophically minded folks among us. As something of a purist myself who believes in the concept of Arete as presented in Mr Pirsig's book, I gotta go with the challenge of DIY. And, speak out against what I see as the weakening of Humanity by the unsupported reliance on modern technology to "save" or "protect" the world from itself. That being said, if I were riding two up on a 1200cc machine, especially in slippery conditions, I would be grateful for ABS and traction control. Someday, when I prefer the idea of a cross country trip with my partner over a day at the races, I'll look into it. Bill

Hey tfc, Forgive me. I am not up on the state of the art of all the current road going models and I tend to think in terms of racing machines. All I know of TC are the recent rules changes at the races here in the US. To comment on how the TC system(s) work, I would need to study up a bit. R