Mounting your battery, Center of Gravity.

[safe]

...all this stuff about traction and vectors is wrong.

Well, now wait a minute...

Is gravity not a real thing to deal with?

Is traction not related to gravity (weight) pressing onto the ground?

...you have to be more specific and identify an error someplace. The blanket refusal to discuss vectors seems completely out of line, if we are going to be scientific then point out how a vector that I've presented might be incorrect. (it's possible that I might have made a mistake... so if you spot one you need to let me know)

All that I've presented has been without any concern for things like steering angle, offset and trail as issues and those do complicate things, however they are less signficant than the Center of Gravity, Countersteer and Traction issues which I've focused on so far. Was that your line of inquiry? I was purposely excluding those issues until later. Steering issues have more to do with balance and establishing a stable turn than initiating the turn through countersteer. (we can discuss this more if that's where you want to go)

Be specific... identify an error.

 

[Tiberius]

...all this stuff about traction and vectors is wrong.

Well, now wait a minute...

Is gravity not a real thing to deal with?

Is traction not related to gravity (weight) pressing onto the ground?

Be specific... identify an error.

Hi safe,

There are too many errors to deal with them all. The reason I'm pointing out the existence of errors is not to re-educate or convert you or John in CR, but simply for the benefit of anyone reading this later.

Actually, this thread has been useful to me, and does contain some nuggets of usefulness. Because of the claptrap posted here, I was forced to go back and re-examine my understanding of the whole subject from first principles. It helps that I have a degree in Physics from a fairly well known British university and have spent 30 years working as as a scientist and engineer.

The wikipedia article is good until it gets onto capsize speed. The Karl Anderson article it links to has an incorrect explanation of why it is more difficult to balance at low speeds.

• Countersteer is real. Both front and rear contact patches countersteer.
  
  When the bike is being ridden, the longitudinal roll axis is near the CG, not the contact patches.
  
  Mounting weight low down does not necessarily improve stability or handling.
  
  Mounting weight to the rear means larger steering inputs are needed to balance the bike.

Safe, I think you've shown that you understand all that, even if others are determined not to. But the recent stuff about traction and vectors has gone off track. Since you ask for specific errors here's a few. You have the working of traction and friction wrong; vector treatment of torque is wrong, examples of rear contact patch behaviour at 0 mph are meaningless because at 0 mph neither contact patch moves.

As I said before, there is good and bad in this thread. But I think its gone as far as it can usefully go and we should all call it a day.

Nick

 

[safe]

You have the working of traction and friction wrong; vector treatment of torque is wrong.

I would have no problem discussing where you saw a problem with my representation of traction. Basically it's a "common sense" idea that traction is at most equal to gravity. In practice there are variations as you travel over different surfaces. Feel free to be more concrete about expressing yourself more on this.

...examples of rear contact patch behaviour at 0 mph are meaningless because at 0 mph neither contact patch moves.

Well, it simplifies things a great deal when you deal with instantaneous vectors rather than getting into all the complexity. I know and you know that the complete formula's are simply too complicated to be dealt with here, but we can get some ballpark ideas to work pretty well. Things like masses in motion are valid even though things like steering geometry (steering angle, offset, trail) introduce mild variations to the results.

Let's just be realistic about the fact that the full charting of the bicycle equation ends up looking like what they presented on wikipedia:

http://en.wikipedia.org/wiki/Bicycle_and_motorcycle_dynamics

...we cannot solve for everything, but we can get some of the basics of masses in motion right.

(notice now speed changes handling behavior)

 

[safe]

The Rear Weight Bike

Moving along (I will still keep up with past questions as they surface) we now see what happens when we go to the opposite extreme. If one extreme is the High Wheel Bike where all the weight is over the front wheel, then the opposite extreme would be to place all the weight over the rear wheel and make a "Rear Weight Bike". I've also simplified things further and located the rear weight at the rear wheel contact patch so we can actually look at what this will do.


First - We need to realize that there is NO WEIGHT on the front tire in this abstraction, so there is no possible way to get any steering force on the front wheel. In a real bike you might have a rear "biased" bike and not go all the way and so we would place a little weight on the front tire and so we would get a little traction. So don't complain about this... "Strike One" about the Rear Weight Bike is that there's no weight on the front wheel, but we are going to get past that and GRANT the front tire some traction anyway. :lol:

Okay, so what happens?

Well if we look at the orthographic picture we see that the steering torque will produce absolutely no rotation... no rotation?... yea... so instead of rotation you get the Center of Gravity being sent off at an angle.

We have amplified the tendency for the rear end to "swing out" in a turn during countersteer... (to the extreme)

A good example of a Rear Weight Bike is a chopper with a really long set of forks sticking waaaaaay out in front of the bike. You can go in a straight line really easily, but try to get into a tight turn and just about everything the bike wants to do is to fight what you are doing.

If you like choppers... well... that's a fashion statement... but from a pure handling perspective the chopper is not anywhere near ideal.

 

[safe]

The Three Possible Designs

Let's just review the three different possible designs:

Front Weight Bike

Balanced Weight Bike

Rear Weight Bike

 

[John in CR]

...There are too many errors to deal with them all. The reason I'm pointing out the existence of errors is not to re-educate or convert you or John in CR, but simply for the benefit of anyone reading this later.

Actually, this thread has been useful to me, and does contain some nuggets of usefulness. Because of the claptrap posted here, I was forced to go back and re-examine my understanding of the whole subject from first principles. It helps that I have a degree in Physics from a fairly well known British university and have spent 30 years working as as a scientist and engineer.

The wikipedia article is good until it gets onto capsize speed. The Karl Anderson article it links to has an incorrect explanation of why it is more difficult to balance at low speeds.

• Countersteer is real. Both front and rear contact patches countersteer.
  
  When the bike is being ridden, the longitudinal roll axis is near the CG, not the contact patches.
  
  Mounting weight low down does not necessarily improve stability or handling.
  
  Mounting weight to the rear means larger steering inputs are needed to balance the bike.

Safe, I think you've shown that you understand all that, even if others are determined not to. But the recent stuff about traction and vectors has gone off track. Since you ask for specific errors here's a few. You have the working of traction and friction wrong; vector treatment of torque is wrong, examples of rear contact patch behaviour at 0 mph are meaningless because at 0 mph neither contact patch moves.

As I said before, there is good and bad in this thread. But I think its gone as far as it can usefully go and we should all call it a day.

Nick

Nick,

The roll axis viewpoint oversimplifies what actually occurs with a bicycle to such an extent that it is clearly inadequate. It applies far more directly to motorcycles than it does to bicycles. The reasons that bicycles don't fit nicely into this narrow view are:

1. The main mass of a bicycle (the rider) changes position relative to the frame during virtually any turn, and can range from a nod of the head to a shift of the entire body.
2. Often, if not typically, the lean angle resulting from countersteer is minimal in relation to the final lean angle deep in the turn, so while yes of course there is some rotation around the dynamic pivot point (point not an axis), much of the lean of a bike in a turn can and does occur as the bike and rider "fall" into the turn which is a rotation around the contact patches.

The mix of these variables can change from rider to ride, or even from one turn to the next, but to dismiss them in any analysis of bicycle behavior is simply wrong.

Regarding the effect on CG of placement of additional weight at different heights, you have to look at a bicycle as a moving body balancing on 2 points above a plane. Then it becomes readily apparent that additional weight had less effect on balance the lower you place it. It's my understanding that the act of balancing is dependent on CG, so if you place it at the plane then you haven't changed CG at all, since balancing hasn't changed. Like I said before, maybe CG is the wrong term to for this analysis, but if so it's because I don't know a better one.

BTW, I never once said low place improves stability or handling, only that placement near the rear contact patch will leave the bike most feeling and balancing like it did without the additional weight with the only change felt being the force is required to move that weight a greater lateral distance.

You should really take more care in the viewpoints you so readily dismiss, because knowledge and education can sometimes cause tunnel vision that obscures seeing the whole picture.

John

 

[Tiberius]

.....much of the lean of a bike in a turn can and does occur as the bike and rider "fall" into the turn which is a rotation around the contact patches.
.....
You should really take more care in the viewpoints you so readily dismiss, because knowledge and education can sometimes cause tunnel vision that obscures seeing the whole picture.

John,

The "falling into the turn" theory is superficially attractive, but is easily seen as bunkum. As soon as you look at the angles involved and start to work out how you control the rate of change of lean angle, you see that it has to be done by moving the contact patches around.

But the real killer is when you consider what happens at the end of the turn. How do you "fall" back upright?

Nick

 

[John in CR]

.....much of the lean of a bike in a turn can and does occur as the bike and rider "fall" into the turn which is a rotation around the contact patches.
.....
You should really take more care in the viewpoints you so readily dismiss, because knowledge and education can sometimes cause tunnel vision that obscures seeing the whole picture.

John,

The "falling into the turn" theory is superficially attractive, but is easily seen as bunkum. As soon as you look at the angles involved and start to work out how you control the rate of change of lean angle, you see that it has to be done by moving the contact patches around.

But the real killer is when you consider what happens at the end of the turn. How do you "fall" back upright?

Nick

Nick,

Sorry but you're not weaseling out of it that easily. Of course countersteer isn't the only way to turn or create lean, though it is how we initiate the imbalance. It's absurd to suggest that we don't instinctively use gravity to our advantage to help create the lean and turn. You can often even hear the difference in the sound of your tires as you have to oversteer to stop the fall in the depth of the turn, and create the imbalance between centrifugal force and gravity to lift back up. Some degree of falling motion takes place in every turn, but how much is mixed in with the countersteer to intitiate a turn and oversteer coming out can vary greatly. Of course corrections take place all the time during a turn, but only to adjust the falling effect of gravity, never the extent of countersteer during a turn. That would just cause you to immediately crash.

I understand that you can't just take my word for it so you can prove it to yourself by:
a. Take your bike out and ride it, doing some lazy turns initiated with very little countersteer, and feel yourself falling into the turn.
b. Look at the geometry. Increase in lean angle can only result from two things; 1. The front wheel turned in the opposite direction (from center) of the direction of the lean, countersteer, which creates a rotation around a point. and 2. Falling in the direction of the lean, which is a rotation of the bike and rider around the contact patches. According to your axis point of view, the maximum lean angle would have to be created during countersteer, but that takes place before the turn even starts, so it can't possibly be true. While motorcycle road racing may come closest to this kind of turn, there is always some fall. It's just that in racing they need to initiate a greater lean at the beginning, since the inverted pendulum of rider and bike will fall too slowly if started at a shallow lean angle. All you have to do is look at any typical bicycle turn to know that the lean angle increases until the full depth of the turn, and it obviously can't be countersteer creating this continuously increasing lean angle. or you'd never turn, only wipe out. Again, just look at the geometry. Once your handlebars come back around past center after countersteer, the only thing that can increase lean angle further is falling into the direction of the turn.

Because your misconception is long rooted with origins in some textbook or lecture, it's probably going to take both a & b for you to let it go and see that I'm correct. Once it clicks for you and the others who've derided me, I do expect an apology.

John

 

[Papa]

Nick,

Sorry but you're not weaseling out of it that easily. Of course countersteer isn't the only way to turn or create lean, though it is how we initiate the imbalance. It's absurd to suggest that we don't instinctively use gravity to our advantage to help create the lean and turn. You can often even hear the difference in the sound of your tires as you have to oversteer to stop the fall in the depth of the turn, and create the imbalance between centrifugal force and gravity to lift back up. Some degree of falling motion takes place in every turn, but how much is mixed in with the countersteer to intitiate a turn and oversteer coming out can vary greatly. Of course corrections take place all the time during a turn, but only to adjust the falling effect of gravity, never the extent of countersteer during a turn. That would just cause you to immediately crash.

I understand that you can't just take my word for it so you can prove it to yourself by:
a. Take your bike out and ride it, doing some lazy turns initiated with very little countersteer, and feel yourself falling into the turn.
b. Look at the geometry. Increase in lean angle can only result from two things; 1. The front wheel turned in the opposite direction (from center) of the direction of the lean, countersteer, which creates a rotation around a point. and 2. Falling in the direction of the lean, which is a rotation of the bike and rider around the contact patches. According to your axis point of view, the maximum lean angle would have to be created during countersteer, but that takes place before the turn even starts, so it can't possibly be true. While motorcycle road racing may come closest to this kind of turn, there is always some fall. It's just that in racing they need to initiate a greater lean at the beginning, since the inverted pendulum of rider and bike will fall too slowly if started at a shallow lean angle. All you have to do is look at any typical bicycle turn to know that the lean angle increases until the full depth of the turn, and it obviously can't be countersteer creating this continuously increasing lean angle. or you'd never turn, only wipe out. Again, just look at the geometry. Once your handlebars come back around past center after countersteer, the only thing that can increase lean angle further is falling into the direction of the turn.

Because your misconception is long rooted with origins in some textbook or lecture, it's probably going to take both a & b for you to let it go and see that I'm correct. Once it clicks for you and the others who've derided me, I do expect an apology.

John

Again, John in CR, you provide wild speculation. Where's the proof?... Where's the numbers?... Where's the links to creditable sources?... Where's the drawings or images depicting the physics you so firmly claim?...

You are not unlike a wannabe college professor explaining verbal ONLY physics to a group of students, sans the aid of descriptive and repetitive drawings scribbled on a blackboard... nor offering text books in order to follow along to CLEARLY grasp the raw substance at the core of your preaching. Essentially, you provide NOTHING but a deranged point-of-view and tainted logic which flies in the face of creditable individuals such as Tony Foale, Vittore Cossalter, Alberto Doria and many, many others.

And I'm willing to wager, that your response to this post will be a mirror image of the same feces....

 

[Papa]

Here's a cute spreadsheet prg that allows you to input and examaine various single-track-vehicle parameters and conditions. You'll need Excel or some other compatible program to use it. Enjoy

http://www.msgroup.org/images/bike.xls

 

[safe]

Handling (While Turning) Not Mentioned

I noticed that a couple of guys have diverged into other areas like the subtle points of holding a lean angle in a turn. That has not been something I got into in the classroom setting.

Basically (I just skimmed a bunch of postings) did anyone have an actual question that was specific to the classroom topic? The Vectors? Orthographic drawings?

There seem to have been questions/discussions on unrelated topics. (I purposely eliminated steering angle, offset and trail from my simplified weight effects class)

I'm just wondering that for our primary topic of weight distribution if we can finally put this one to bed.

We can sum up the three design choices:

Front Weight Bike - Good steering response, poor braking behavior.

Balanced Weight Bike - Decent steering response, good braking.

Rear Weight Bike - Poor steering response, excellent braking. (especially on the rear wheel)

The High Wheel Bike

Vectors

Simplified Orthographic Drawing

Momentum

Braking the High Wheel Bike

Turning the High Wheel Bike

Weight Distribution Options

The Safety Bike

Multiple Vectors for the Safety Bike

The Rear Weight Bike

 

[John in CR]

Papa,

"Wild speculation", "deranged point of view", you call yourself a professional designer yet you don't understand enough about how a bicycle moves to understand that a bicycle can only lean (or lean further) to the left when it is turned to the right or falls to the left...Talk about incompetence! This concept is simple enough that it requires no proof, no numbers, no formulas. Do your own research to improve your understanding, because I don't have the slightest desire to do it for you, or better yet take your bike for a ride and see for yourself, but be careful that your visual point of reference from on the bike doesn't confuse what is easily felt. btw, JohnRobHolmes already posted a graphic for you that clearly shows both components of a turn.

It really amazes me that a concept so simple can create so much grief. Since I'm so very wrong Papa, present a single logical argument instead of only spewing derogatory comments. I've boiled what I've been saying all along about how a bike actually turns down to one simple statement, so go ahead and demonstrate by any means you feel is appropriate how an increased lean to the left can occur with the front wheel pointed straight or turned to the left with a rotation around the CG instead of around the contact patches.

John

 

[Papa]

so go ahead and demonstrate by any means you feel is appropriate how an increased lean to the left can occur with the front wheel pointed straight or turned to the left with a rotation around the CG instead of around the contact patches.

John

Several posts back, myself and a few others, tried in vain to explain the 'whys' and 'hows', but you hard-headedly refuse to listen... or even consider what was stated. Further still, you recklessly criticized Tony Foale's CoG calculator, claiming it was 'faulty'... and you offered NO evidence to substantiate your statement. Then you accused me of altering the results. Further still, I posted a statement by Paul Dean (in post dated Sep 16, 2008 12:05 pm) containing an easy to understand explanation about "roll", "longitudinal roll axis" and approximately where it was located. But again, you refused to even consider its validity or the highly respected individual who created it. And throughout your entire 6 weeks of posting in this thread, you could've easily repositioned your batteries in half-a-dozen different locations, and discovered first-hand where optimum is. And now you have audacity of expecting us/me to wade through the same stinking waters again????

Suffice to say, John in CR, you obviously have issues...

 

[safe]

Suffice to say, John in CR, you obviously have issues...

What seems to have happened is that "John in CR" does not have a physics background and bases his opinions on vague impressions he gets while riding combined with his own logic about how things might work. My goal is to at least present him the door to walk through so that he deals with the issues coming from a scientific perspective. Once someone gets stuck on an idea it requires double the effort to get them to change that idea because the natural tendency is to "save face" for what you said in the past.

It's a little like this issue with Obama and him saying that the surge in Iraq could never work. Objective reality tells us that the surge worked, but for Obama to admit that his estimation of things was in error would be to admit that he's capable of error. It fits into the whole "Me Generation" frame of mind where truth is "relative" and all that matters is that people get their way. American culture is getting less and less able to give up turf for the sake of truth.

The goal should always be "truth first" and "ego second".

We should honestly pursue the truth about how the underlying physics works with bike geometry. However, the true complexity is so difficult to reduce to simple eqautions (impossible really) that it leaves room for those with no foundation to exist for a long time (or forever) while never having to admit their theories are not part of basic science.

I'm still waiting for any questions about the basics as presented in these orthographic diagrams. As long as you exclude the complexities of steering angle, offset and trail the problem gets reduced significantly. If all our bikes had vertical forks then this would all be easy. (well... at least a whole lot easier)

 

[Tiberius]

But the real killer is when you consider what happens at the end of the turn. How do you "fall" back upright?

Nick

Nick,

Sorry but you're not weaseling out of it that easily.

John,

Since you will not, or cannot, engage with the maths and physics of this simple piece of dynamics, I pointed out a simple and obvious fundamental flaw in your theory. Now, that's not really weaseling, is it?

Nick

 

[johnrobholmes]

I would like to know the answer as well. Also, if we cannot pivot the wheels under the CG (rotation about CG in space) during a turn there would be no way to keep balance. Riding on a treadmill is possible because when we "fall" a bit we can pivot the bike back underneath us. Falling implies a relative relationship between our own center of mass and the CoM of the earth (the object that we fall to). Balancing is therefore a pivoting around our center of mass, and the earths center of mass. Both the earth and our bike pivot in space when we correct our balance, merely equal and opposite action and reaction.

Balancing requires support to be directly underneath the CG of an object.
Without support the object "falls".
To stop the fall support must be returned under our CG, or we must have an equal or greater centripetal force opposite to the vector of gravity.

 

[Papa]

The "falling into the turn" theory is superficially attractive, but is easily seen as bunkum.

Agreed.

IMO, "fall" usually implies one direction only, downward - it also fails to describe the actual dynamics taking place (unless, of course, you're about to consume a slice of asphalt pie). Thanks, but i'll stick with the terms, "Roll", "Rotate" or 'Rotation' because they are the most commonly used terms - and they best describe what is actually occuring.

 

[John in CR]

Great any more bandwagon jumpers? You guys are hilarious. Can you really not understand that I used the term "fall" as a distinction between "roll" around the axis at the tire patches (caused by gravity in excess of the effects of centripetal force after considering lean angle leverage) verses the "rotation" around the CG or Dynamic Pivot Point that occurs during countersteer? Think about how a tree "falls" if you still don't get it. Let's not mince words when there is apparently a significant conceptual difference. The 4 of you have insisted that roll, rotation, or whatever you want to call it occurs only around the CG. I disagree and have maintained all along that the bike and rider also "roll" around around the contact patches (especially the rear because it is also the axis point of any pitch), and this part of the roll behavior can be dominant and can't be ignored WRT how battery placement affects the steering of a bicycle.

You've pissed me off enough to go ahead and do the research for you, and right now I'm knee deep in Vittore Cossalter, who so far is talking about roll being around the contact patches and even changing CG in terms of "energy potential". I'm confident that we'll be able to come to a consensus that includes you letting go of your misconceptions, or as a better description, your incomplete conceptions. A bike most certainly doesn't rotate only around it's CG, and I'm not talking about stationary or very slow speeds either.

For those on the sidelines, all this banter does have a point. Earlier in the thread we had good input about the effects of different placements, but understanding why through an accurate understanding of how a bike moves will enable us to better predict those effects.

John

PS- Johnrobholmes, do I need to include discussion of how CG height has no effect on lean angle (except for the negligible effect due to tire width, which we can ignore for bicycles), or have you let go of that misconception already?

 

[johnrobholmes]

PS- Johnrobholmes, do I need to include discussion of how CG height has no effect on lean angle (except for the negligible effect due to tire width, which we can ignore for bicycles), or have you let go of that misconception already?

Go ahead and try to find it, or better yet try it out! I already know how bikes handle with different CG heights. Simple physics, an object with a lower CG can lean farther while keeping support underneath. A clown punching bag can lean further the heavier it is at the bottom (lower CG), same as a rider balancing in a turn. You must have support underneath to be in a stable turn.



I agree that you can fall into a turn initially, but I maintain that the point of reference for any object is the center of mass (gravity). When a rider "falls" into a turn with a rotation about the tire it is not the same as a tree falling. The rider is in motion, he has a change in his direction with the fall and the tires must follow to keep balance. The "fall" is the first part of countersteer when the tires are coming out from underneath the CG, as the object has already entered the turn but the support has not. This is a relative relationship. The turn is not referenced from the tires, it is referenced from the CG of the object (which is the axis of rotation for any falling object).

 

[safe]

I'm still waiting for any questions about the basics as presented in these orthographic diagrams.

So far no critical things have been said about the "basics" of simple bodies in motion as have been presented by the orthographic drawings. (things like weight on the front verses weight on the rear)

Are we then in agreement about the basics?

I've heard some debates about terminology (is it a "roll" or a "fall") but no one seems willing to stick their neck out to actually refute the basic laws of physics. (probably a good idea :lol: )

The High Wheel Bike

Vectors

Simplified Orthographic Drawing

Momentum

Braking the High Wheel Bike

Turning the High Wheel Bike

Weight Distribution Options

The Safety Bike

Multiple Vectors for the Safety Bike

The Rear Weight Bike

 

[safe]

Maximum Traction

This is going off on a slightly different tangent, but it is important. Traction is a combination of the "stickiness" of the rubber touching the road surface (assuming street conditions) combined with the weight applied to the contact patch.

I'll state this as something that is rather obvious:

There is an advantage to balancing the rider/bike in the center between the two tires (like the safety bike) because that means that the front and rear tires can achieve maximum useful traction.

If all the weight is on the front the traction on the front tire increases proportionally, but it's a bad design because of the inability to brake very hard without tipover.

If all the weight is on the rear wheel then the rear braking force is strong, but the steering traction is reduced to nothing.

So one of the easiest arguments for balanced weight is that is divides the traction between front and rear. Being able to slide forward a little adds more weight on the front tire, slide a little back and you get a little more on the rear. Fortunately this comes naturally because on braking you tend to be pushed forward and when (on a motorcycle) you roll on the power on the exit of the turn your body gets thrown back. So there's a lot of wiggle room for front-to-back body position to enhance traction.

People that ride in the dirt know about forward and back body movements to shift the weight around so that you can drift over loose surfaces in a controlled slide.

 

[John in CR]

PS- Johnrobholmes, do I need to include discussion of how CG height has no effect on lean angle (except for the negligible effect due to tire width, which we can ignore for bicycles), or have you let go of that misconception already?

Go ahead and try to find it, or better yet try it out! I already know how bikes handle with different CG heights. Simple physics, an object with a lower CG can lean farther while keeping support underneath. A clown punching bag can lean further the heavier it is at the bottom (lower CG), same as a rider balancing in a turn. You must have support underneath to be in a stable turn.

I agree that you can fall into a turn initially, but I maintain that the point of reference for any object is the center of mass (gravity). When a rider "falls" into a turn with a rotation about the tire it is not the same as a tree falling. The rider is in motion, he has a change in his direction with the fall and the tires must follow to keep balance. The "fall" is the first part of countersteer when the tires are coming out from underneath the CG, as the object has already entered the turn but the support has not. This is a relative relationship. The turn is not referenced from the tires, it is referenced from the CG of the object (which is the axis of rotation for any falling object).

Johnrob,

Here's a discussion including the math supporting that speed and turn radius alone determine lean angle, not CG height. http://www.msgroup.org/forums/MTT/topic.asp?TOPIC_ID=312 . I do believe that CG height affects the rate of change in lean angle, so I think I understand where that perception comes from.

The blow up punching clown obtains its self righting behavior from its wide somewhat rounded base and significant weight there, and isn't really irrelevant to the lean angle discussion. It can however be adapted to my point about very low placement not affecting CG in terms of balancing. First narrow its base and make it more rigid, like a bike tire. Then put some weight at the top to make it more like a bike in terms of balancing and leaning. Now changing the amount of weight at the bottom has no significant effect on balancing or the forces required to keep it balanced when imbalance occurs when you lean it over.

Regarding "fall", I'm sorry I used the word. I did so because you can actually feel yourself falling into a turn, and because the bike is like an inverted pendulum, the fall is through increased lean like a tree. Of course a bike is in motion, and it's the speed and turn radius that result in the force to slow and stop it, as well as reverse it. I wasn't talking about the lowering of the CG during countersteer as falling, though we have no disagreement there.

The disagreement lies in the roll and rotation of the bike. During countersteer we agree that rotation occurs around the CG if the rider maintains a rigid position wrt the frame, though the axis point of the frame rotation will typically will be lower because the rider changes position. Once you steer back past neutral to actually turn, the bike can only increase lean angle by rolling around the axis of the contact patches.

Now maybe Safe with his racing style of riding and Papa with his recumbents, I don't know b/c I've never ridden one, get to or near full lean during countersteer and hold it through the turn, but I don't on my upright bike. On a typical turn I let gravity create most of the lean unless it's a sharp turn. A gradually decreasing turn radius slows this roll or "falling into the turn" motion until the middle of the turn where the radius becomes small enough at that speed to overcome gravity and lift back upright.

To address Tiberius' earlier question about coming out of a turn, getting back upright is different, because the geometry is different. The front wheel can be steered in the proper direction to reduce the lean, so I expect there typically is more roll around the CG mixed in, unless you are able to accelerate out of the lean like on a motor cycle. Before you go "wait, how can coming out of the turn be different?", it most certainly is. A perfect example is in racing, where braking takes place before the turn, but you accelerate while still in the turn on the way out. Even tracks are shaped differently at the entrance and exit of a turn.

John

 

[johnrobholmes]

With the model you can see both the lean angle of the CoG as well as the real lean angle of the bike change as you vary width of the front tire or heigth of the CoG.

So with a tire that has ANY width, CG does indeed affect lean angle of the bike. Open up the calculator James posted and try it out. The lean angle in reference the the CG remains constant. The lean angle in reference to the bike changes with changes in CG (with lower CG taking more lean for the same speed, curve radius, and lateral acceleration). You should read the posts more carefully before making conclusions, you just posted evidence against your own statements.


LOL at turning in and out of corners being different, and somehow having different roll centers. Its like physics will change depending on the riders mood and intentions!

 

[safe]

Now maybe Safe with his racing style of riding and Papa with his recumbents, I don't know b/c I've never ridden one, get to or near full lean during countersteer and hold it through the turn, but I don't on my upright bike.

I get to roughly a 30-40 degree angle of lean (at most) in the turns. I ride up onto the lip of my road racer type tires. Given that I'm only going 35 mph while leaning like this it's not so fast that I need quicker performance, but it's nice to have such a responsive bike because when I'm in a tough spot and need to "save it" then the bike assists in that. Several days ago there was this turn that I kept going at faster and faster and deeper and deeper into the lean angle with each lap... I realized that I had overshot my pivot point (the time when I had to commit to the turn) and I was able to reverse course onto an exit route. If my bike wasn't as quick responding as it is I'm sure I would have wrecked.

So good handling... excellent handling... has it's survival benefits as well as it just feeling better.

For people that don't lean very much you can mostly ignore countersteer... it's only when leaning the bike is important (performance riding) that you really need the basics to be on your side.

 

[Papa]

The 4 of you have insisted that roll, rotation, or whatever you want to call it occurs only around the CG.

I never stated or specifically implied that roll or rotation "ONLY" occurs around the CoG. My "rotational" references were generalized and specifically aimed at your childish defiance of the existance of "roll", rotation" or "roll axis" within single-track-vehicle dynamics. (note the examples below to which I refer

"A bike doesn't roll. A bike can't roll other than its wheels. If you tried to draw a line from the rear like in those motorcycle graphics, it would be up somewhere in the rider's body, but I still wouldn't call it a roll axis."

"The only things "rotating" on a bike are the tires, crank and the headset."

"The concept of roll axis relative to a bike is erroneous, because there is no roll."