M1Combat

If you have traction available you could start adding speed and the bike would begin to stand up? You could lean your upper body further into the turn to lift the bike a hair and use the extra traction to feed in some power?

The "COMBINED" CG height will be exactly the same height (given equilibrium) no matter where YOU are on the bike given the same speed and radius. Hanging off certainly moves YOUR CG to the inside of the corner (but moves the bikes out a little...) and the COMBINED CG stays at the same height. One would want to pick the bike up off the edge of the tire while coming out for a couple reasons... One, you want to save the edge to maximise mid-corner speed through the race. Two, you can put more power down when the tire isn't right on the edge. Three... (this ones a little tough to follow for some) the tire is smaller the closer you get to the edge... This means that when you roll over to the edge, if you keep the same speed, your RPM's will rise... You can use that extra HP WHILE picking the bike up to help add drive out of the turn... If you're in an endurance race you MAY be able to save a bit of fuel by hanging way off and using the larger portion of the tire. That is... if the extra wind resistance isn't offsetting the fuel savings... Each tire will have a lean angle where it will generate the most grip. You want to use THAT lean angle mid-turn as far as I know. To do that AND go fast/er, you hang off which lowers the combined CG and will require more centrepital force (AKA Speed) to achieve equilibrium... You hang off just enough and use just enough speed at the "right" lean angle for your tire/setup/geometry/etc combination to maximise grip... Or at least that's how I see it, but I've never even done Code's L1 class... I'd LOVE to, but I have more suspension and motorcycle to buy before I can get on the track as well as in school. School will come before track, but I will be using the school AND track days to get a setup started so I may as well start with the suspension I'll be using on track... In racing, EVERYTHING counts. It's all about energy management.

I've heard it said that when Michael Schumacher closes his eyes and visualizes a single lap... He opens his eyes typically within a hundredth of a second or two of his typical lap times.

In my humble experience... It seems to me that Dunlop tends to make a rear tire that has a somewhat flatter profile than the competition. It works well coming out, but sacrifices some mid-corner effectiveness. I think your problem would be completely solved by hanging farther off the bike, or moving to a 180, or going to a different brand. A pound less pressure in the front may help as well?

Sounds about right... Which would be why it's called "Anti-Squat" as opposed to "Pro-Lift" .

The entire bike lifts. The important part of geometry that has the affect is the relationship between the rake angle and swingarm angle. The rear wheel moves in an arc, the front in a straight line. As you get on the gas you want the wheelbase to stay the same. You need what they call "anti-squat" on the rear. The axle and swingarm pivot are the important points (along with the action of the chain). If the axle is lower than the swingarm pivot point, then the force applied in a forward direction will attempt to push the swingarm under the motorcycle. Due to the fact that it's fixed at the front, it will rotate. It rotates downward. This lifts the rear of the bike. The key is to try to keep the wheelbase as static as possible so the steering geometry doesn't change as you apply power. Two things change when one end goes up/down more than the other... Wheelbase and rake. The less these change, the easier it is to keep the bike near/at it's limit. It's why I hate peaky IL4's . I'll take an engine with linear power over one that's peaky any day of the week.

I didn't say "Buell". I said "Buell XB". If you haven't ridden one... well... Just keep talking out your ass then I guess. 20K miles and only one issue. The trans output shaft seal failed because I dropped it into first w/o the clutch TWICE from a dead stop. It just seeped a little and the dealership replaced it under warranty (a two year warranty I might add) in about 40 minutes. No trouble other than that. Besides... This is a thread about handling... What's the deal with coming in here and talking about a niche market sport-touring bike? You brought it up though... The S2/S3 bikes are a good handling bike for touring bikes. I completely understand that Buell went through some growing pains but AT LEAST THEY RECALLED STUFF. Other companies have FRAMES that crack and they refuse to admit it... The XB's have had two recalls in four years. Both on the first model. One was for the wheel bearings, and the other for the kick-stand. Both were supply issues as opposed to engineering issues. The parts were recalled/replaced for free and BMC made a good effort to actually contact EACH AFFECTED CUSTOMER to let them know. Just an FYI... Based on warranty dollars spent per unit sold... The XB series is THE most reliable motorcycle money can buy. I understand that none of this will change the sour taste in your mouth. Sorry your S2-"T" (Please note the "T" there...) handled like a "T"ouring bike . Aside from that... Recalls are recalls. They happen to lots of bikes. It's the companies that WON'T recall stuff that really suck. You think just because a company refuses to DO recalls that the engineered a superior product? Keep thinking that .

I think what I do is most like what Woody describes. Sort of throwing the bike around under me with my knees. Both knees on the tank in the center, and then sliding out to one side as the lean angle goes up. Of course this is only between turns in a chicane type setting. For your average "single turn" I get off the bike a little ways before I get on the brakes and stay there until I'm at WOT coming out.

You can corner just fine with the front in the air. That said though... If you ARE cornering with the front in the air, you're leaving a lot of speed on the table and you weren't at the limit to begin with.

I agree . I have a passion for Buells. Just to keep you up to date... Jeremy McWilliams, Mike Cicotto, Pascal Picotte and Rico Panzkopher will be riding Buell XBRR's in the 200. I think they'll have a fighting chance but of course the teams are somewhat new to the Daytona. Mike Hale may be in it too, but Innovative's team may not get a bike soon enough. Here's to hoping though. Try a Buell , You'll like it if you like bikes that handle well.

Watch the Daytona 200 .

I've never been on a purpose built race bike, but I have a Buell XB12R and it seems to handle very well. It seems to be one of the most capable handling bikes made (right up there with the 999R, 916, 749R and RSVR) and it seems very easy to access. It seems very stable through high speed sweepers over bumps with no damper, it is VERY flickable and responsive (as it should be with 250GP like geometry) and the low reving V-Twin creates a power band that is easy to access and has no suprises. I'm sure I'll get a few heaters for this, but I think it's the best handling production bike man has devised. The thing is... Buell ships the bike with tires that don't seem to be matched well with the radical geometry. With the stock tires it wants to stand under mid-corner braking (not so much if you're just trailing a little rear brake) and it takes (IMO) too much effort to the inside bar to keep it leaned over near the lean angle limit. Swap out to Sportecs, Diablos, Qualifiers or Pilots and both issues disappear. When Erik Buell is asked about it he typically responds that there aren't enough Shawn Higbee's in the world. I would tend to agree because I've learned that proper form eliminates these issues as well. It's just that hanging way off and being a stickler for form all the time isn't practical. When tearing up canyon roads, sure... but sometimes I just want a moderate pace. I also didn't like the wet weather characteristics of the stock Dunlop tires. Mid-corner line changes are effortless and it's been proven many times that the XB frame is capable of higher mid-corner speeds than just about anything else out there.

I think the problem that we may be running into is that IMO there isn't a "answer" to whether the CG should be high or low. I think it depends on what you want out of the bike. I think a bike with a high CG will feel like a "light steering bike" and a low CG will feel heavier. The "answer", as I've said before, is that you define what you want the bike to DO first, then you go about getting there by tuning rake/trail, CG height, wheelbase, angular relation between the swingarm and rake, bar leverage, frame stiffness, seating position, suspension setup, wheel size, etc, etc, etc... The ONLY other thing we can do IMO is decide what the effect of raising or lowering the CG is when leaving everything else alone. That said... I ride an XB12R. It's widely regarded as one of the best handling bikes you can buy (like top three, and most places put it AT the top, but really , I'm not here to bench race ) and it's got one of the lowest centers of gravity of any production bike and it's mass is EXTREMELY centralized. It also has a very steep rake angle and very little trail and heavy flywheels when compared to most other bikes so I really can't tell you which of those is "most" responsible for the good handling. As I said above though, I suspect it's the entire package... In any case... The roll center should be between the combined CM and the bikes CM... Probably very close to the bikes CM. It would make sense to do it that way because that should allow the bike to be as light feeling as possible because it's rolling around a spot very close to it's own CM. I really wish I had the right books to read...

Interesting... I was looking at the running man from a completely different direction... I would ass u me that that fulcrum is where you trip him and the end of the lever arm would be his CM. The fulcrum is also the RC (ass u ming a rigid skeleton...).

WRT the higher CM making it "easier" to initiate lean... That's all I was saying . Not that it would also be inherently faster. The fulcrum would of course be the roll center. Look at a teeter-totter... the fulcrom is the roll center. Of course, ours isn't attached to anything in particular, but it's there. "With a human low and long as recommended by the experts for turn in/cornering....just where do you figure the cm to be? Up high on top like a sledgehammer balanced on the end of its handle? Really?" No. My guess would be just a few inches above a line drawn from the top of one tire to the top of the other in side view. I certainly see your point with the two handled hammer thing but it didn't serve the purpose of the point I was trying to make. I wasn't assuming that the RC of the hammer was at the hammer head. "I agree with tzrider who said something about easier not being the same as faster." Me too . "And...at the end of the day, what if the centralization of mass might be the defining parameter for turn in speed." Centralization is obviously important but of course you'll run into the law of diminishing returns with that and the gyroscopic properties of the crank shaft will need to be looked at as well. That said, it's all a trade off. Larger flywheels add stability. It's all a package... Which is why I think that "at the end of the day"... The CG height needs to be placed where it needs to be placed to maximize traction when leaned greater then 45 degrees. I could care less about "lever effort". I care about quick. That's why I ride an XB12R. It is a little harder to snap into lean at higher speeds, but it does it very quickly if you use your muscles. It's still a whole package though... radical geometry for sharpness, large flywheels to stabilize, VERY centralized mass etc... "So, the longer the arms, the less effort needed to initiate spin. But the slower the roll/spin will be. The shorter the arm(s), the more effort needed to initiate spin. But the faster the mass will roll/spin. The closer the cm is to cr, effectively speaking, the shorter the arm(s) will be. " I would agree with those three statements. There's still a fine line though... You don't want a bike that takes so much lever effort that it becomes difficult to manage the strength that you exert, or makes you prone to using both hands to initiate lean. "So...where is the force applied? Is any applied at the top? Or the center? Or just at the patch? Hmmm..." At the tire patch obviously, but also from the top (your other arm ). We "should" hang off well before we initiate turn in. This gives gravity a longer lever to pull the bike over using our mass. Forces applied in the center... Twisting forces I would imagine. Torque applied to the frame by the steering head and running through to the swingarm. "hey, why do stock cars and sprint cars run speedways counterclockwise????? " Because most people find it easier to turn left.

Newton said... "Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it." We counter steer to the right, the bike flops over to the left because all of it's mass would like to continue on in a straight line. We can then proscribe a left hand turn. The height of the CM is effectively defining the length of the lever arm that we use to make this happen. The lever arm would be defined as the distance between the tire patch (where we are exerting force) and the CM. Simple mechanics will tell us that the length of a lever arm will directly affect the efficiency of our system. I think we both understand that. On to the ghost rider... I agree... The bike does fall over slowly but you'll find that it never proscribes a constant arc, and if it does a slow wobble, it never goes "straight". It's an ever tightening arc until it slows down enough that the inertia isn't great enough to support the system. It's newtons first law that causes this too. The inertia built into the system as a mass at a given (but slowing) velocity is what holds it "mostly" upright. As the system loses velocity, it has less inertia to hold itself up, but as it leans more the rake/trail turn the wheel inwards as it's designed to and tightens the turn all while bleeding the least amount of energy as possible. I propose that if you were to lock the steering head straight ahead then a bike would fall over just as quickly at 100MPH as if it was just standing still. Obviously it's gravity that causes this, but I believe that gravity is a very small part of why a bike drops into a turn quickly. Inertia is, IMO, the VASTLY overwhelming force. Once IN a turn and at equilibrium, then yes, it's inertia (or angular momentum?) that is directly countering the force of gravity. Now, again, we get to the low vs. high CG thing... Which attains a higher cornering speed given the same lean angle? Here's my take... a low CG requires less lean angle with a given speed and velocity. The angle at which the gravitational and centrepital forces are acting through the tire patch is defined by the lean angle. You essentially waste less force pushing outwards when you use less lean angle. Of course, each tyre type will have an optimal lean angle, so the real answer is that you want the CG height to be at the height that takes advantage of the tires characteristics. "If it was just forward momnetum, the bike could lean over at any time." It does... constantly... back and forth. It's the self righting geometry combined with inertia and gravity that cause this. Bikes never go straight until after something like 250MPH where they cease to be a counterstering system. That said, they return to being a countersteering system again somewhere above 300MPH. I've done the wheel on an axle in my hands experiment. I understand gyroscopes. As a side note, it's newton's first law that makes gyroscopes work the way they do as well. As far as picking apart the hammer thing ... have at it .

"Like I said before, a ghost bike has to practically stop before gravity overcomes the gyroscopic effects of the wheels and makes it fall down" My bad... I thought you wereimplying that gyroscopic precession was the dominant force keeping the motorcycle up until it slows down. 2 - They're all the same. The mechanics of a tank slapper are exactly what keep a ghost bike upright. It just doesn't turn into a tank slapper (hopefully anyway). 3 - Same as above I think. WRT the hammer analogy, I was trying to make the point that with a high CG, the bottom will move a lot easier. With a low CG, the bottom will require more force to be moved. To answer your question, yeah, the handle would most likely rotate all the way around until it hits the ground again and then the hammer would begin falling to one side. That goes beyond the scope of the discussion though. My only point was how much force it would take to get the bottom moving (which is where our contact pactch is, and is the only location we have to affect change in the direction of our bike). "The mass distribution of a motorcycle and rider is nothing like a sledgehammer." I disagree, but that's ok. It's not "exactly" like a sledge hammer balanced on one end, but it's close enough to make the point I was aimed at, which was that the further away from the CM that our tire patches are, the easier it is to initiate lean angle. "You brought up center of roll in a previous post and I asked you where that was. You never answered." Sorry about that . I'm not entirely certain, but it's somewhere between the combined CM of rider/bike and the tire patch. "And vice versa on the balancing trick. Not sure of the relevance of that analogy either. Are you implying that the distance your hand travels is somehow related to inertia? I don't get it. " Certainly not . I'm implying that with a long handle (higher CG) the CG itself moves a greater distance at 5 degrees of lean angle, and that to bring the tire patches (or bottom of the handle) back under the CM to balance the hammer, it will need to be moved farther than one with a short handle (or lower CG relative to our tire patches). I wasn't talking about inertia there, I was talking about a system being either in or out of equilibrium. The way to change direction on a bike (or, to take a bike somewhere other than where it's current state of equilibrium would have taken it), whether it be mid-corner, corner entry, or on corner exit is to remove it from equilibrium. This analogy shows ME that a bike with a low CG will require less movement of the bars to affect change to it's state to either remove it from or return it to equilibrium. It may be described as some to be "twitchy", but only if they are being ham fisted with the bars.

It's not gyroscopic precession that keeps the ghost bike up. When the bike starts to fall over the rake/trail cause the wheel to turn to the inside of the turn and will right the bike. It's inertia that causes the initial "snap" in of lean angle. A high CG will facilitate this. Stand a slegde hammer on either end and kick the bottom... One way will have the hammer falling just like a bike (at initial counter steer), the other will produce a broken toe. Take that same hammer and balance it on your hand... Now let it fall 5 degrees to one side... With a long handle (high CG height) you'll need to move the base farther to regain balance. With a 2" handle, you'll hardly have to move the base at all... Now my question is... What are the changes in handling characteristics when already leaned in? I would think that the lower CG'd bike would be easier to make line changes with and would be more stable.

The tires have a sweet spot. In lean angle, slip angle temperature etc. That's exactly where you need to be for best speed. Of course... That's obvious which is why the conversation is about CG height. The CG height needs to be at a height that allows you to take best advantage of the tires sweetspot. That's the answer. There's no real advantage to moving the cg up or down other than that. It needs to be in one place for flickability, it needs to be in another place for maximum traction. You move it to that other place by hanging off.

Which bike needs to be traveling faster to maintain equilibrium given that both bikes mass is the same but one has the lower CG height?

Hmmmm.... "The interesting thing I found last night reading through Tony Foale?s book is that a lower CofG requires more lean angle then a higher CofG." A lower CG wil have a shorter moment arm. Therefore greater force will be needed to overcome the force of gravity (or a longer arm). The force being the centripidal variety being exerted towards the outside of the turn (speed causes this). You can either use LESS lean angle to increase the length of the arm, or you can use more speed to exert enough force on the arm you have. Keep in mind though, that your limit is traction. There's no point in designing a bike that's a great deal more capable than it's tires. My thoughts seem to contradict what you are saying Tony says... There must be some confusion somewhere... It is my opinion that "within reason" there are no benefits to moving the CG up or down. The CG needs to be at the "correct" height. That "correct" height will be defined by the available amount of traction and lean angle. It needs to be in a place that is complimented by the other factors. Of course moving it will have an effect on the way the bike feels (higher CG should make a bike more flickable, lower CG should make a bike feel a little more stable and should find equilibrium at less angle of lean with a given speed). You can't isolate one area. Other things inherent in the geometry of a motorcycle can have the same or similar effect. Less rake makes a bike more flickable as well. Larger flywheels can make a bike more stable.

The roll center (or roll "axis" if you prefer) is not at the contact patch, and the LONGER the moment arm is the easier/quicker it'll roll in. The cg height certainly DOES affect the lean angle required to get around a turn... More importantly the COMBINED cg height matters as well. Draw a free body diagram and you'll understand.

Wouldn't RPM's rise (given the same speed) as lean angle increases? Lean angle reduces the circumfrence of the tire...

Ken... I have a Buell Firebolt. I also need to keep a VERY minimal ammount of pressure on the inside bar to maintain lean angle... Unless I hang off properly. Also... The original D207's that come with the Buells (except for the "CityCross" model) cause this as well due to the fact that they are not a sharply profiled tire. The rear especially is very flat compared to most other sport bike tires. I switched to the Metzeler Sportec M1 and as long as I hang off a little, they work wonderfully. No tendency to stand at all unless I use the front brake mid-turn. Anyway, I just wanted to mention that if your friend still uses the D207's, it's worth it to swap to Pilots, Sportecs or Diablos.

I'll bet this explains exactly why it should or shouldn't be done . http://ist-socrates.berkeley.edu/~fajans/T...fEQRoutines.pdf