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If anyone speaks German, de:Fahrradfahren seems to be about bicycle physics. -- Christopherlin 03:25, 3 April 2006 (UTC)
Copied from the article:
"A rider stays upright on a bicycle by steering the bicycle so that the point where the wheels touch the ground stays underneath the center of gravity. Once underway, this effort is largely replaced by physical forces generated by the rotation of the wheels which produce a remarkable "self-steering" effect. The angular momentum of the wheels and the torque applied to them by the ground generates a phenomenon called precession, by which the wheel turns, or trails, toward whichever side the bicycle tilts. Like the rider's steering adjustments, this motion automatically returns the contact point of the wheel directly under the center of gravity. These forces, perhaps aided at very high speeds by the gyroscopic effect of the spinning wheels,4 are sufficiently strong that a riderless bicycle going down a slope will stay upright by itself."
The effect described in sentences 2, 3, and 4 above IS the gyroscopic effect, so to say in sentence 5 that it is perhaps aided by the gyroscopic effect is confusing. The more important effect, according to Jones and others, is that of trail, described in the third paragraph of the 'Bicycle physics' section. Rracecarr 18:54, 11 May 2006 (UTC)
All of these issues were corrected by me back in February. On May 5 someone reverted the entire article back a few months. Even the first sentence here is poor. The goal isn't just to keep the centre of gravity over the line between the wheels -- the rider also wishes to drive the bike where he wants it to go. While turning, the centre of gravity must lean into the turn (not stay over the wheels) or the bike will tip over. - JethroElfman 16:26, 15 May 2006 (UTC) Okay, I restored the section. Perhaps someone would like to restore the entire article. The physics section could be tinkered with further. For instance, the "geometry of the front forks" has two components. One is how the contact of the tire to the road trails where the steering axis intersects the road. The second is the angle of attack of the steering axis. The exaggerated angle of a chopper is less stable, yet it is presumably advantageous to have the slight angle of a regular bike. I don't understand why it isn't perpendicular like a furniture caster. The length of trail is 1.5" for standard use, and up to 2.5" for racing duty. Increased distance adds stability for hands-free or aero bar operation, but makes cornering stiff. The speed-wobble section could be reworded. I don't think the comparison to a shopping-cart wheel is entirely accurate in this case. JethroElfman 16:43, 15 May 2006 (UTC)
I think you are putting too much emphasis on precession. I thought that the Jones article settled that precession isn't such a big deal for bicycles.
For motorcycles it is, so it's good to explain the principles involved.
In that regard, the rear wheel is restrained from precessing because it is rigidly attached to the frame, whereas the front wheel can turn the head axis.
Even so, as the bike turns through the corner, the rear wheel is thereby allowed to precess and thus aid in turning the mass of the bike.
The first paragraph offends my memories of grade 10 physics class. Inertia is not a force. Its effects are applied to the bike through the tire contact to the road.
I think your descriptions of trail and head angle are still too intertwined. Trail turns the wheel by gravity when the bike is leaning. Head angle generates a gravitational force to turn the wheel when the wheel is turned off centre, even if the bike is perfectly vertical.
If trail is kept to zero, a leaning bike's wheel won't turn regardless of the head angle (you have to extend the curvature of the forks forward to do this).
Oh, and Jones claims that negative trail makes a bike entirely unrideable, so what's your reference that says it's rideable but difficult?
What's your reference for the note about long-wheel-based recumbents. It sounds interesting and I'd like to read that one.
I still don't understand why head angle isn't just 90 degrees. Is it to keep the rider from going over the handlebars when braking perhaps?
Your internal links are done with html references rather than the simple square-bracket approach. Why is that? - JethroElfman 16:40, 16 May 2006 (UTC)
In the new diagram, things are labeled differently from how I learned them. I thought rake was the angle of the steering axis from vertical, which in the diagram is labeled "head angle" (well, 90 degrees minus what I thought was rake is so labeled). Someone on wikipediea appears to agree with me: rake and trail. Here is another random example: www.performanceoiltechnology.com/rake_and_trail.htm However, I also found a reference agreeing with AndrewDressel: www.sheldonbrown.com/gloss_ra-e.html ???? Rracecarr 19:10, 16 May 2006 (UTC)
I've changed the links I can from html references to the simple square-bracket approach. I've found and moved the Zinn reference to come at the end of the trail paragraph. I've moved gyroscopic effects to last, but left it verbose because it is the one effect that varies with speed. I've added a reference for the low and high speed instabilities I mention. I've added information about making turns. AndrewDressel 01:27, 17 May 2006 (UTC)
Added quick analysis of braking forces, but forgot to login first AndrewDressel 12:42, 7 June 2006 (UTC)
All of the topics mentioned in the article apply equally to motorcycles as well. Moreso in fact due to their larger mass. -- Hooperbloob 13:56, 7 June 2006 (UTC)
Kudos on the bicycle->bike revision, it does the job perfectly. -- Hooperbloob 15:17, 20 June 2006 (UTC)
Then the last step would involve renaming the article itself to "Bicycle & motorcycle physics" ? -- Hooperbloob 02:11, 21 June 2006 (UTC)
I notice on my bicycle that I shift my body away from the direction of a turn. That is, on left-hand turn lean the bike left, but keep a body position almost vertical. This is to counteract the way the front-wheel trail wants to straighten the bike back up. In motorcycle racing however, they lean way into the turn (with a knee stuck out). Is this because the gyroscopic effect of the wheels is trying to stand the bike up, and needs counterbalanced? JethroElfman 16:02, 30 May 2006 (UTC)
Having read through the steering section, I've noticed that the description of a number of items (particularly in the 'counter-steering' portions) don't square with my own experience riding. In particular, there are two items I feel might warrant changes: 1. The process of counter-steering a motorcycle through a turn does not, at least in my riding experience, involve a discernable deflection in the actual path of the motorcycle. It's possible that there is some small path change, but in my experience (at street speeds) it's not a significant (or even noticable) effect.
2. There is a statement to the effect that 'all turning on a motorcycle uses counter-steering' which is not strictly true, I don't believe. While it is probably the case that basically all steering on a motorcycle involves deflection of the front wheel, the cause of that deflection is not necessarily counter-steering. The shifting of body weight on the motorcycle (without input to the handlebars) can cause the motorcycle to steer (although it is markedly less efficient than the use of the bars), and any wheel deflection involved is due to frame geometry effects as opposed to active counter-steering.
I think perhaps a wording change is in order there (and the citation of the 'no-bs' bike isn't without the potential for controversy).
Would anyone else like to chime in here before I go and edit this section? [The above entry is by user Saturn_V timestamped 15:39 13 June 2006]
"there isn't another way [other than counter steering] to lean the combined center of gravity of a bike and rider,"
How do people fall off bikes? The model of a rider/bicycle system as the rider is but a 160 lbs. seat is flawed. Humans have the ability to become off balance first, and use the regaining of balance as the mechanism of turning.
A process I see like this:
The key points:
What matters is that in counter steering the rider is a reacting agent and in intuitive steering the rider is an active agent.
I guess I'm asserting that the article needs to reflect this.
Earth to McFly ( talk) 22:22, 24 November 2007 (UTC)
I studied this as part of my engineering degree on control theory. It's unfortunately too long ago for me to remember off the top of my head the maths or the details, but the conclusion is interesting. Bicycles are examples of positive pole systems. This explains the counter steering needed, and also other features of the dynamics such as how easy it is to make it unstable. If you put too much gain in and try to counter steer too much you go over, so there's only a limited range of gain you can use in your control system (the rider). This sounds a similar analysis to the Eigenvalues but using a different technique and a different way of interpreting the results. —Preceding
unsigned comment added by
213.146.159.254 (
talk)
12:07, 30 January 2008 (UTC)
Unicycle physics and Physics of a rolling coin Wow! Anyone know who is 80.168.225.36? The "fmt hdrs as per manual of sty" looks good. AndrewDressel 13:56, 23 June 2006 (UTC)
The_Anome "rm unnecessary cite: all this can be confirmed from the other cites given below" at 22:49 on 23 June 2006, but I think he misunderstood why I included the link. Instead of just restoring it, I made a new section and listed a handfull of other examples. It may not be appropriate for this article, but it gives me a chuckle. AndrewDressel 01:23, 24 June 2006 (UTC)
After reading the FA requirements, especially for lead section, I'm thinking of changing the title to "Bicycle and motorcycle dynamics". Dynamics is a much better fit than physics. Otherwise, in order to be complete, the article would need to be expanded to include performance, efficiency, etc. Given the very different power plants and speed ranges of bicycle and motorcycles, I believe this would be impractical. Comments? AndrewDressel 14:32, 26 June 2006 (UTC)
I probably won't be able to go through this article in the detail I'd like until this weekend, but I'll try and put the things I find that I haven't had the time to correct yet and maybe some other folks can help? Some of these are more questions of style than actual problems...
I'll update this list as I find more (or fix things). Saturn V 16:58, 29 June 2006 (UTC)
between a number and the unit of measurement. For example, instead of 18mm, use 18 mm, which when you are editing the page, should look like: 18 mm.<div class="references-small"><references/></div>
.{{subst:js|User:AndyZ/monobook.js/footnotehelper.js}}
to your monobook.js file (mine is located at
User:AndyZ/monobook.js) and then bypass your browser's cache by pressing: Mozilla/Safari/Konqueror: hold down Shift while clicking Reload (or press Ctrl-Shift-R), Internet Explorer: press Ctrl-F5, Opera: press F5. In editing mode, click on the "Footnote creater" tab that appears.AndrewDressel 01:33, 24 June 2006 (UTC)
1. This article is awfully light on non-science explanations - it would be nice if instead of "Bicycle and motorcycle dynamics is the science of the motions and forces of bicycles and motorcycles. It includes how they balance, steer, and brake." and so on that it was a bit simplified for the casual reader. For example, something like "Bicycle and motorcycle dynamics is the science of the steering, balancing, and breaking of bicycles and motorcycles." or something (I imagine that is incorrect but hopefully helps someone).
2. "Examples of misconception" scares me - if it were me I'd nuke it - it seems pointless and something the reader should decide. Ditto for the mention of "incorrect" online examples (which, BTW, in these articles one really needs to be more specific then just "online").
3. "careful" in the lead is really redundant and speculative without attribution - "in fact", again, makes me think that the article is trying to prove some sort of point.
4. The lead should really have less stubby "paragraphs" 5. Referencing is a bit odd, I'd recommend some sort of script to convert those links to some other more accessable reference style.
6. "The design charactersics of a bike can affect the stability in the following ways"
7. "A bike is a nonholonomic system because its outcome is path-dependent" and now the writer has lost me :(. This makes it difficult to evaluate the article... RN 08:03, 29 June 2006 (UTC)
Would love to find a reference for:
Until one is found, it can stay here. - AndrewDressel 00:50, 4 August 2006 (UTC)
I’ve tried to change the citations a bit, away from the style of the articles named in the todo list. The problem with it is that it’s difficult to follow while reading the article—it’s hard to tell whether a given citation refers to a newspaper article or a published paper. Also, with the other style, there is no need to maintain a second list of the same sources in the references section.
In the process, I omitted some sources because I did not think they are really usable. Since the article is about physics, it’s probably a good idea to stick to published scientific works for all important points. On this topic, could you please check whether Hand’s thesis has been published anywhere?
As for the misconceptions, I don’t think the section should remain in that form at all. If there is a different point of view on the issue, it should be explained properly in the article—even if it’s technically wrong. — xyzzy n 17:49, 4 August 2006 (UTC)
I cannot believe that stayed incorrect as long as it did. Maybe someone tweaked it and I didn't notice. More likely, I just goofed. The equation that was there was for lean away from vertical, but the drawing of course shows lean up from horizontal. Anyway, great thanks to 128.227.67.147 (in their first and only edit so far) for noticing it and fixing it. - AndrewDressel 03:14, 8 February 2007 (UTC)
While I may be biased, because of the work I have done on this article, I gave it an "A" because I believe it meets these criteria:
If anyone disagrees, I'd love to hear about it. - AndrewDressel 18:40, 1 March 2007 (UTC)
"These roles of gyroscopic effect and precession are often given as the prime reasons that bicycles and motorcycles are inherently stable."
"While they have an effect at significant speeds, the role of caster angle, and the rider's steering action, actually provide the bulk of a bike's inherent stability at lower, nominal speeds."
"This is easily proven. As a first example, a bicycle rider at even the slowest speed of 1 or 2 MPH can easily keep the bike stable. The contribution of gyroscopic and precession effects are absolutely negligible at such a speed (only the rider's steering and body movements influence stability at such speeds)."
"Moreover, consider an ice skater on one skate, or a pogo stick rider, neither of which has any gyroscopic or precession effects in action: the skater or pogo stick are stabilized by "driving" the vehicle in question manually. This means simply riding -- keeping the surface that contacts the ground, on average, under the center of mass."
"As another test, one can try locking the steering of a bicycle or motorcycle, and then giving it a push - it will fall over just as quickly as leaving it stationary and letting go."
"A bike with a free steering mechanism can be given a push at a relatively slow speed, and due to caster effect, will move smoothly with stability -- there is no rider, and there are no significant gyroscopic effects whatsoever."
Let's see how far the reviewers like the article now that most things seem to have been cleaned up. I went through it once and didn't see anything *obvious*. Nominated as a GA. Severo T C 23:25, 17 May 2007 (UTC)
It is getting pretty late and i shall come back with more feedback as i see that i have already given enough to work/chew on. -- Kalyan 20:30, 2 June 2007 (UTC)
"This is necessary in order to balance the sideways friction against the road which is the centripetal force due to the turn, with gravitational forces due to the lean."
"a bike and their components"
"Friction"
"These forces make bicycle accelerate forwards or sideways (if moving in a circle at constant speed)."
- AndrewDressel 16:03, 15 June 2007 (UTC)
I removed the mention of wheelbase as a factor in the lean angle in the introduction by LarRan. This would need a reference and should be included in the section on turning, especially the equation used to calculate lean angle from turn radius and forward speed. - AndrewDressel 15:50, 27 August 2007 (UTC)
I've moved some recent addtions to here:
At this point, after the good article review, these all would need a reputable (on the order of "Bicycling Science" by Wilson, "Motorcycle Dynamics" by Cossalter, or a published paper) to be included. - AndrewDressel 01:37, 19 September 2007 (UTC)
I believe this material is better suited to the Bicycle brake systems article, partly because it is only about bicycle braking, but also because it is more about the mechanics of braking than the dynamics of bikes. However, before I insert it there, it needs a clean up:
It all came back again, even the typos ("aren no"), so to avoid some kind of revert battle I tried to clean it up. It still overlaps longitudinal stability some. However, the sections on wet weather and icy weather really have nothing to do with Bike Dynamics. They belong in the Bicycle brake systems article if anywhere. Even there, the icy weather section is more of a "how to" than wikipedia wants. - AndrewDressel 21:21, 15 October 2007 (UTC)
The examples of braking, whether front,rear, wet or icy, were for bicycles. However the physics apply to both bicycles and motorcycles. Wet and icy conditions do affect the braking and steering of a bike, that's why they were inserted.
Your edits to do with braking friction reduce the clarity. Limiting and sliding friction are different and should be written as such. Read Wilson (Bicycling Science). Verity1234 08:08, 20 October 2007 (UTC)
Since centrifugal forces do not exists they should not be referred to in a physics article. They could be identified as a colloquialism and the misconception could then be addressed.
A free body diagram within the section is a must as it represents how physicists assess such things. And on such a diagram "centrifugal" would not be found.
People often believe a force is necessary to keep something going as a apposed to necessary for changing its motion. Referring to a centrifugal force is similar. Nothing is pushing the rider outward, something is pushing the rider inward. This is neither nuance nor a small matter.
Earth to McFly ( talk) 22:16, 24 November 2007 (UTC)
This claim remains unsourced since October 2007, so I've moved it here. - AndrewDressel ( talk) 16:55, 14 February 2008 (UTC)
In order to uphold the quality of Wikipedia:Good articles, all articles listed as Good articles are being reviewed against the GA criteria as part of the GA project quality task force. While all the hard work that has gone into this article is appreciated, unfortunately, as of February 13, 2008, this article fails to satisfy the criteria, as detailed below. For that reason, the article has been delisted from WP:GA. However, if improvements are made bringing the article up to standards, the article may be nominated at WP:GAN. If you feel this decision has been made in error, you may seek remediation at WP:GAR. GA review – see WP:WIAGA for criteria
I've chosen to delist this article from GA status mostly do to many chunky passages and manual of style infractions. These are listed in detail below.
Detailed comments
-- jwanders Talk 00:05, 13 February 2008 (UTC)
Yup, I'm happy to simply re-instate this. Thanks for all your prompt hard work; first time an article that I've had to delist has received any sort of reply. Kudos! -- jwanders Talk 19:39, 14 February 2008 (UTC)
There is something fundamentally wrong here. As anyone learning to ride a bicycle knows, you can have the easiest, most self-steering bicycle in existence and you will still fall off. After a painful learning process you discover the knack of making small adjustments, and once that becomes a reflex, the experience of riding is just the same as if the bike stays upright on its own.
The way a bike stays upright is by making constant small corrections. I'm not a physicist but dynamic instability is the term that comes to mind - possibly dynamic equilibrium (neither has a Wiki entry that is remotely relevant here). It is highly misleading to suggest that some bikes are self stabilising. Until you get into the realms of powered computer-controlled systems, e.g. Segway, this is simply not true. Yes, a lot of rake increases stability but it does not eliminate the need for corrections.
There is an interesting essay on the subject, here How two bike mechanics taught the human race to fly ProfDEH ( talk) 07:33, 8 May 2008 (UTC)
I've been taking a look at this article with the idea of doing some copy-editing, and I can tell immediately that this will be a real challenge—the article is basically in terrific shape right now. I'll keep looking, though. And perhaps another role I can play here is Sample Layperson. When reading the History section it jumped out at me that it was " Karl von Drais himself" (emphasis is mine). I had to follow the wikilink to find out who he was. Could we add a small phrase, within commas or parentheses, about this notable person (notable not just to science, but to the article at hand as well). I'm not the best person to word this, but it would be something like: "In the early 1800s Karl von Drais, inventor of the velocipede (a bicycle prototype) showed that a rider..." This might be appreciated by your lay readers. -- AnnaFrance ( talk) 18:44, 27 May 2008 (UTC)
In speaking of a bike as an inverted pendulum, the point is made that balancing is easier with a higher center of mass, but that a lower center of mass actually seems easier to the rider when stationary. I gather from this section that balance actually is easier with a lower center of mass when stationary. But then the last sentence says that touring cyclists are advised to carry loads low, i.e., maintain a low center of mass. This confuses me. They would be in motion more of the time, so wouldn't they want to maintain the higher center of mass? Extra note: Isn't it about time to archive this talk page? -- AnnaFrance ( talk) 14:54, 29 May 2008 (UTC)
Do you think it would improve this opening section to take the second paragraph and insert it between the 1st and 2nd sentences of the first? Then you would be introducing the idea of instability, defining the terms stability and instability, and finally introducing the types of instability. Also, I wish something more could be done with the Modes section. It's a section that consists of one line, and much of that is redundant. But it is needed to balance out the Design Criteria section. If you have any free time, you might want to see if there's any way the Modes opening section could be expanded.
Old Business: I like the way you included the second-class lever explanation in the Center of Mass Location section. I think it helps.
Archiving talk page: I've studied up on archiving talk pages, and I think I understand. Let me try it late tonight. That way the activity should be done for the day here, and we can label the archive as being Apr 06 - May 08, starting fresh tomorrow with June 1. -- AnnaFrance ( talk) 19:46, 31 May 2008 (UTC)
This page is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
The comment(s) below were originally left at Talk:Bicycle and motorcycle dynamics/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.
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While I may be biased, because of the work I have done on this article, I gave it an "A" because I believe it meets these criteria:
|
Last edited at 18:40, 1 March 2007 (UTC). Substituted at 14:21, 1 May 2016 (UTC)
Archive 1 has been created with a link at right. Archive 2, when needed in the future, should be a new subpage (same as creating an article) titled "Talk:Bicycle and motorcycle dynamics/Archive 2" and the link added to the template on this page's code. For further information on archiving see Wikipedia:How to archive a talk page. -- AnnaFrance ( talk) 04:24, 1 June 2008 (UTC)
In reference to a change I just made in the sentence:
The "it can be fatal" was originally "they can be fatal". When I made that change, I was assuming that "wobble or shimmy" was referring to 2 words for the same (one, singular) thing. The longer I stare at the sentence, though, the less sure I am that this is what was meant here. Did you mean them to be one thing in this particular sentence, or two?
Old business: I think the opening paragraph of the Instability section works better now (and you eliminated the repetitions). -- AnnaFrance ( talk) 15:56, 2 June 2008 (UTC)
-- AnnaFrance ( talk) 18:33, 5 June 2008 (UTC)
The handlebars issue is a minor one. I've changed the sentenced discussed above. About the bolding: I hear that WP generally discourages bolding outside of titles. Since there are so many sections in this article, it seemed to me that any extra bolding might be seen as screen clutter, so I've taken it all out. -- AnnaFrance ( talk) 19:40, 6 June 2008 (UTC)
In the first paragraph of the Tires section, could we get a brief definition of the term "normal" in parentheses? I think the lay reader can infer the gist of most of the technical terms in this article (contact patch, side slip, etc.), but this one may be a little advanced. -- AnnaFrance ( talk) 20:20, 7 June 2008 (UTC)
I'm going to go back through the article now with an extensive list of WP:MOS guidelines, to try to find any small points missed before. (If anyone would rather that I stop with the nitpicking, please just say so.) One small item that I think would be worth some real effort to get perfect is the opening definition of the article's subject. As a grammatical sentence, I don't think it works all that well:
Bicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles, in entirety or in parts, due to the forces acting on them during balancing, steering, braking, and suspension.
The part that's bothering me is "the forces acting on them during...suspension". That doesn't sound right. Grammatically, it would certainly be best to have a fourth -ing, but "suspending" obviously is ridiculous. Is there a way of referring to all four elements that would be appropriate to all of them? Or am I not interpreting this correctly? -- AnnaFrance ( talk) 17:59, 9 June 2008 (UTC)
While I finish up the final run-through on the text, I'm going to ask my husband, Sfbart ( talk) (who was a professional web developer), to take a look at the image placement. According to the Wikipedia Manual of Style, they prefer the first image to be on the right, then alternate down the page, if possible, to avoid what they call "stackups". We do have a bit of a stackup at one point on the page. I'll ask him to see if he can untangle the stack and alternate sides at least occasionally, without moving any image out of its basic position within the article. -- AnnaFrance ( talk) 22:13, 16 June 2008 (UTC)
In the beginning of this section, one of the features of an idealized bike is:
Could this be changed to:
-- AnnaFrance (talk) 15:20, 19 June 2008 (UTC)
What's next for this article? Try to get a peer review? -- AnnaFrance (talk) 16:27, 20 June 2008 (UTC)
This discussion ( centrifugal force vs inertia) has appeared here before, and has since been archived. As the article on that subject currently states: "Despite the name, fictitious forces are experienced as very real to those actually in a non-inertial frame. Fictitious forces also provide a convenient way to discuss dynamics within rotating environments, and can simplify explanations and mathematics." Centrifugal force provides a simple way to explain leaning in a turn, a convenient way to calculate the lean angle necessary, and so is used in this article.
The current wording; "the external forces are due to gravity, inertia, contact with the ground, and contact with the atmosphere"; does not actually call inertia a force any more than it calls gravity a force. More detail about reference frames is provided just three paragraphs later.- AndrewDressel ( talk) 14:25, 26 June 2008 (UTC)
It appears to me that the capsize speed and the weave speed are reversed, both in the text, in the eigenvalue plot and in the PDF reference [17] by Meijaard, et al. My own experience is that at low speed a bicycle will "capsize" (fall over without any weaves), while at high speed on a poorly designed bicycle the weaves can increase in amplitude until "failure". I'm not an expert, nor a prior contributer to Wikipedia, so I hesitate to make any changes. Comments? —Preceding unsigned comment added by 70.19.235.105 ( talk) 16:41, 13 July 2008 (UTC)
Maybe I missed it in the article, but the main reason for self stability is trail. When the front wheel is leaned, the pavement pushes up (opposing gravity) at the contact patch, and since the contact patch is "behind" the pivot axis (trail), the result is an inwards yaw torque on the front wheel, causing it to steer inwards. Once above some minimum speed, the inwards torque generates enough steering input to result in vertical stability. Note that gyroscopic effects can be eliminated, for example using skates on ice or skis on snow, and "trail effect" would still result in vertical stability. Trail also creates caster effect, which dampens overcorrection due to momentum. Jeffareid ( talk) 01:26, 18 October 2008 (UTC)
To me, terms like stability and riderless bicycles are synonomous with self stability. Note that the Jones article involved real testing of bicycles, not just a paper exercise. Riderless bicycles with negative fork trail fell over almost immediately, riderless bicycles with normal amounts of fork trail were self stable above a minimum speed, riderless bicycles with large amounts of fork trail slowed to a near stop before falling over. I'd call that evidence of a relationship between trail and self-stability.
I'm not claiming that trail is the only source of self-stability, just that it's the main source. Every web article I've found defines a strong correlation between stability and trail, some specifically using the term "self-stability". The fact that trail tends to steer the front tire towards the direction of lean is mentioned in this article. To me, it's this inwards steering reaction that results in self stability. Are you stating that trail has no effect on self stability, in spite of real world experiments that appear to establish a relationship between the amount of trail and the amount of self-stability? Is there some hidden factor I'm missing here? Jeffareid ( talk) 19:35, 18 October 2008 (UTC)
This page is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
If anyone speaks German, de:Fahrradfahren seems to be about bicycle physics. -- Christopherlin 03:25, 3 April 2006 (UTC)
Copied from the article:
"A rider stays upright on a bicycle by steering the bicycle so that the point where the wheels touch the ground stays underneath the center of gravity. Once underway, this effort is largely replaced by physical forces generated by the rotation of the wheels which produce a remarkable "self-steering" effect. The angular momentum of the wheels and the torque applied to them by the ground generates a phenomenon called precession, by which the wheel turns, or trails, toward whichever side the bicycle tilts. Like the rider's steering adjustments, this motion automatically returns the contact point of the wheel directly under the center of gravity. These forces, perhaps aided at very high speeds by the gyroscopic effect of the spinning wheels,4 are sufficiently strong that a riderless bicycle going down a slope will stay upright by itself."
The effect described in sentences 2, 3, and 4 above IS the gyroscopic effect, so to say in sentence 5 that it is perhaps aided by the gyroscopic effect is confusing. The more important effect, according to Jones and others, is that of trail, described in the third paragraph of the 'Bicycle physics' section. Rracecarr 18:54, 11 May 2006 (UTC)
All of these issues were corrected by me back in February. On May 5 someone reverted the entire article back a few months. Even the first sentence here is poor. The goal isn't just to keep the centre of gravity over the line between the wheels -- the rider also wishes to drive the bike where he wants it to go. While turning, the centre of gravity must lean into the turn (not stay over the wheels) or the bike will tip over. - JethroElfman 16:26, 15 May 2006 (UTC) Okay, I restored the section. Perhaps someone would like to restore the entire article. The physics section could be tinkered with further. For instance, the "geometry of the front forks" has two components. One is how the contact of the tire to the road trails where the steering axis intersects the road. The second is the angle of attack of the steering axis. The exaggerated angle of a chopper is less stable, yet it is presumably advantageous to have the slight angle of a regular bike. I don't understand why it isn't perpendicular like a furniture caster. The length of trail is 1.5" for standard use, and up to 2.5" for racing duty. Increased distance adds stability for hands-free or aero bar operation, but makes cornering stiff. The speed-wobble section could be reworded. I don't think the comparison to a shopping-cart wheel is entirely accurate in this case. JethroElfman 16:43, 15 May 2006 (UTC)
I think you are putting too much emphasis on precession. I thought that the Jones article settled that precession isn't such a big deal for bicycles.
For motorcycles it is, so it's good to explain the principles involved.
In that regard, the rear wheel is restrained from precessing because it is rigidly attached to the frame, whereas the front wheel can turn the head axis.
Even so, as the bike turns through the corner, the rear wheel is thereby allowed to precess and thus aid in turning the mass of the bike.
The first paragraph offends my memories of grade 10 physics class. Inertia is not a force. Its effects are applied to the bike through the tire contact to the road.
I think your descriptions of trail and head angle are still too intertwined. Trail turns the wheel by gravity when the bike is leaning. Head angle generates a gravitational force to turn the wheel when the wheel is turned off centre, even if the bike is perfectly vertical.
If trail is kept to zero, a leaning bike's wheel won't turn regardless of the head angle (you have to extend the curvature of the forks forward to do this).
Oh, and Jones claims that negative trail makes a bike entirely unrideable, so what's your reference that says it's rideable but difficult?
What's your reference for the note about long-wheel-based recumbents. It sounds interesting and I'd like to read that one.
I still don't understand why head angle isn't just 90 degrees. Is it to keep the rider from going over the handlebars when braking perhaps?
Your internal links are done with html references rather than the simple square-bracket approach. Why is that? - JethroElfman 16:40, 16 May 2006 (UTC)
In the new diagram, things are labeled differently from how I learned them. I thought rake was the angle of the steering axis from vertical, which in the diagram is labeled "head angle" (well, 90 degrees minus what I thought was rake is so labeled). Someone on wikipediea appears to agree with me: rake and trail. Here is another random example: www.performanceoiltechnology.com/rake_and_trail.htm However, I also found a reference agreeing with AndrewDressel: www.sheldonbrown.com/gloss_ra-e.html ???? Rracecarr 19:10, 16 May 2006 (UTC)
I've changed the links I can from html references to the simple square-bracket approach. I've found and moved the Zinn reference to come at the end of the trail paragraph. I've moved gyroscopic effects to last, but left it verbose because it is the one effect that varies with speed. I've added a reference for the low and high speed instabilities I mention. I've added information about making turns. AndrewDressel 01:27, 17 May 2006 (UTC)
Added quick analysis of braking forces, but forgot to login first AndrewDressel 12:42, 7 June 2006 (UTC)
All of the topics mentioned in the article apply equally to motorcycles as well. Moreso in fact due to their larger mass. -- Hooperbloob 13:56, 7 June 2006 (UTC)
Kudos on the bicycle->bike revision, it does the job perfectly. -- Hooperbloob 15:17, 20 June 2006 (UTC)
Then the last step would involve renaming the article itself to "Bicycle & motorcycle physics" ? -- Hooperbloob 02:11, 21 June 2006 (UTC)
I notice on my bicycle that I shift my body away from the direction of a turn. That is, on left-hand turn lean the bike left, but keep a body position almost vertical. This is to counteract the way the front-wheel trail wants to straighten the bike back up. In motorcycle racing however, they lean way into the turn (with a knee stuck out). Is this because the gyroscopic effect of the wheels is trying to stand the bike up, and needs counterbalanced? JethroElfman 16:02, 30 May 2006 (UTC)
Having read through the steering section, I've noticed that the description of a number of items (particularly in the 'counter-steering' portions) don't square with my own experience riding. In particular, there are two items I feel might warrant changes: 1. The process of counter-steering a motorcycle through a turn does not, at least in my riding experience, involve a discernable deflection in the actual path of the motorcycle. It's possible that there is some small path change, but in my experience (at street speeds) it's not a significant (or even noticable) effect.
2. There is a statement to the effect that 'all turning on a motorcycle uses counter-steering' which is not strictly true, I don't believe. While it is probably the case that basically all steering on a motorcycle involves deflection of the front wheel, the cause of that deflection is not necessarily counter-steering. The shifting of body weight on the motorcycle (without input to the handlebars) can cause the motorcycle to steer (although it is markedly less efficient than the use of the bars), and any wheel deflection involved is due to frame geometry effects as opposed to active counter-steering.
I think perhaps a wording change is in order there (and the citation of the 'no-bs' bike isn't without the potential for controversy).
Would anyone else like to chime in here before I go and edit this section? [The above entry is by user Saturn_V timestamped 15:39 13 June 2006]
"there isn't another way [other than counter steering] to lean the combined center of gravity of a bike and rider,"
How do people fall off bikes? The model of a rider/bicycle system as the rider is but a 160 lbs. seat is flawed. Humans have the ability to become off balance first, and use the regaining of balance as the mechanism of turning.
A process I see like this:
The key points:
What matters is that in counter steering the rider is a reacting agent and in intuitive steering the rider is an active agent.
I guess I'm asserting that the article needs to reflect this.
Earth to McFly ( talk) 22:22, 24 November 2007 (UTC)
I studied this as part of my engineering degree on control theory. It's unfortunately too long ago for me to remember off the top of my head the maths or the details, but the conclusion is interesting. Bicycles are examples of positive pole systems. This explains the counter steering needed, and also other features of the dynamics such as how easy it is to make it unstable. If you put too much gain in and try to counter steer too much you go over, so there's only a limited range of gain you can use in your control system (the rider). This sounds a similar analysis to the Eigenvalues but using a different technique and a different way of interpreting the results. —Preceding
unsigned comment added by
213.146.159.254 (
talk)
12:07, 30 January 2008 (UTC)
Unicycle physics and Physics of a rolling coin Wow! Anyone know who is 80.168.225.36? The "fmt hdrs as per manual of sty" looks good. AndrewDressel 13:56, 23 June 2006 (UTC)
The_Anome "rm unnecessary cite: all this can be confirmed from the other cites given below" at 22:49 on 23 June 2006, but I think he misunderstood why I included the link. Instead of just restoring it, I made a new section and listed a handfull of other examples. It may not be appropriate for this article, but it gives me a chuckle. AndrewDressel 01:23, 24 June 2006 (UTC)
After reading the FA requirements, especially for lead section, I'm thinking of changing the title to "Bicycle and motorcycle dynamics". Dynamics is a much better fit than physics. Otherwise, in order to be complete, the article would need to be expanded to include performance, efficiency, etc. Given the very different power plants and speed ranges of bicycle and motorcycles, I believe this would be impractical. Comments? AndrewDressel 14:32, 26 June 2006 (UTC)
I probably won't be able to go through this article in the detail I'd like until this weekend, but I'll try and put the things I find that I haven't had the time to correct yet and maybe some other folks can help? Some of these are more questions of style than actual problems...
I'll update this list as I find more (or fix things). Saturn V 16:58, 29 June 2006 (UTC)
between a number and the unit of measurement. For example, instead of 18mm, use 18 mm, which when you are editing the page, should look like: 18 mm.<div class="references-small"><references/></div>
.{{subst:js|User:AndyZ/monobook.js/footnotehelper.js}}
to your monobook.js file (mine is located at
User:AndyZ/monobook.js) and then bypass your browser's cache by pressing: Mozilla/Safari/Konqueror: hold down Shift while clicking Reload (or press Ctrl-Shift-R), Internet Explorer: press Ctrl-F5, Opera: press F5. In editing mode, click on the "Footnote creater" tab that appears.AndrewDressel 01:33, 24 June 2006 (UTC)
1. This article is awfully light on non-science explanations - it would be nice if instead of "Bicycle and motorcycle dynamics is the science of the motions and forces of bicycles and motorcycles. It includes how they balance, steer, and brake." and so on that it was a bit simplified for the casual reader. For example, something like "Bicycle and motorcycle dynamics is the science of the steering, balancing, and breaking of bicycles and motorcycles." or something (I imagine that is incorrect but hopefully helps someone).
2. "Examples of misconception" scares me - if it were me I'd nuke it - it seems pointless and something the reader should decide. Ditto for the mention of "incorrect" online examples (which, BTW, in these articles one really needs to be more specific then just "online").
3. "careful" in the lead is really redundant and speculative without attribution - "in fact", again, makes me think that the article is trying to prove some sort of point.
4. The lead should really have less stubby "paragraphs" 5. Referencing is a bit odd, I'd recommend some sort of script to convert those links to some other more accessable reference style.
6. "The design charactersics of a bike can affect the stability in the following ways"
7. "A bike is a nonholonomic system because its outcome is path-dependent" and now the writer has lost me :(. This makes it difficult to evaluate the article... RN 08:03, 29 June 2006 (UTC)
Would love to find a reference for:
Until one is found, it can stay here. - AndrewDressel 00:50, 4 August 2006 (UTC)
I’ve tried to change the citations a bit, away from the style of the articles named in the todo list. The problem with it is that it’s difficult to follow while reading the article—it’s hard to tell whether a given citation refers to a newspaper article or a published paper. Also, with the other style, there is no need to maintain a second list of the same sources in the references section.
In the process, I omitted some sources because I did not think they are really usable. Since the article is about physics, it’s probably a good idea to stick to published scientific works for all important points. On this topic, could you please check whether Hand’s thesis has been published anywhere?
As for the misconceptions, I don’t think the section should remain in that form at all. If there is a different point of view on the issue, it should be explained properly in the article—even if it’s technically wrong. — xyzzy n 17:49, 4 August 2006 (UTC)
I cannot believe that stayed incorrect as long as it did. Maybe someone tweaked it and I didn't notice. More likely, I just goofed. The equation that was there was for lean away from vertical, but the drawing of course shows lean up from horizontal. Anyway, great thanks to 128.227.67.147 (in their first and only edit so far) for noticing it and fixing it. - AndrewDressel 03:14, 8 February 2007 (UTC)
While I may be biased, because of the work I have done on this article, I gave it an "A" because I believe it meets these criteria:
If anyone disagrees, I'd love to hear about it. - AndrewDressel 18:40, 1 March 2007 (UTC)
"These roles of gyroscopic effect and precession are often given as the prime reasons that bicycles and motorcycles are inherently stable."
"While they have an effect at significant speeds, the role of caster angle, and the rider's steering action, actually provide the bulk of a bike's inherent stability at lower, nominal speeds."
"This is easily proven. As a first example, a bicycle rider at even the slowest speed of 1 or 2 MPH can easily keep the bike stable. The contribution of gyroscopic and precession effects are absolutely negligible at such a speed (only the rider's steering and body movements influence stability at such speeds)."
"Moreover, consider an ice skater on one skate, or a pogo stick rider, neither of which has any gyroscopic or precession effects in action: the skater or pogo stick are stabilized by "driving" the vehicle in question manually. This means simply riding -- keeping the surface that contacts the ground, on average, under the center of mass."
"As another test, one can try locking the steering of a bicycle or motorcycle, and then giving it a push - it will fall over just as quickly as leaving it stationary and letting go."
"A bike with a free steering mechanism can be given a push at a relatively slow speed, and due to caster effect, will move smoothly with stability -- there is no rider, and there are no significant gyroscopic effects whatsoever."
Let's see how far the reviewers like the article now that most things seem to have been cleaned up. I went through it once and didn't see anything *obvious*. Nominated as a GA. Severo T C 23:25, 17 May 2007 (UTC)
It is getting pretty late and i shall come back with more feedback as i see that i have already given enough to work/chew on. -- Kalyan 20:30, 2 June 2007 (UTC)
"This is necessary in order to balance the sideways friction against the road which is the centripetal force due to the turn, with gravitational forces due to the lean."
"a bike and their components"
"Friction"
"These forces make bicycle accelerate forwards or sideways (if moving in a circle at constant speed)."
- AndrewDressel 16:03, 15 June 2007 (UTC)
I removed the mention of wheelbase as a factor in the lean angle in the introduction by LarRan. This would need a reference and should be included in the section on turning, especially the equation used to calculate lean angle from turn radius and forward speed. - AndrewDressel 15:50, 27 August 2007 (UTC)
I've moved some recent addtions to here:
At this point, after the good article review, these all would need a reputable (on the order of "Bicycling Science" by Wilson, "Motorcycle Dynamics" by Cossalter, or a published paper) to be included. - AndrewDressel 01:37, 19 September 2007 (UTC)
I believe this material is better suited to the Bicycle brake systems article, partly because it is only about bicycle braking, but also because it is more about the mechanics of braking than the dynamics of bikes. However, before I insert it there, it needs a clean up:
It all came back again, even the typos ("aren no"), so to avoid some kind of revert battle I tried to clean it up. It still overlaps longitudinal stability some. However, the sections on wet weather and icy weather really have nothing to do with Bike Dynamics. They belong in the Bicycle brake systems article if anywhere. Even there, the icy weather section is more of a "how to" than wikipedia wants. - AndrewDressel 21:21, 15 October 2007 (UTC)
The examples of braking, whether front,rear, wet or icy, were for bicycles. However the physics apply to both bicycles and motorcycles. Wet and icy conditions do affect the braking and steering of a bike, that's why they were inserted.
Your edits to do with braking friction reduce the clarity. Limiting and sliding friction are different and should be written as such. Read Wilson (Bicycling Science). Verity1234 08:08, 20 October 2007 (UTC)
Since centrifugal forces do not exists they should not be referred to in a physics article. They could be identified as a colloquialism and the misconception could then be addressed.
A free body diagram within the section is a must as it represents how physicists assess such things. And on such a diagram "centrifugal" would not be found.
People often believe a force is necessary to keep something going as a apposed to necessary for changing its motion. Referring to a centrifugal force is similar. Nothing is pushing the rider outward, something is pushing the rider inward. This is neither nuance nor a small matter.
Earth to McFly ( talk) 22:16, 24 November 2007 (UTC)
This claim remains unsourced since October 2007, so I've moved it here. - AndrewDressel ( talk) 16:55, 14 February 2008 (UTC)
In order to uphold the quality of Wikipedia:Good articles, all articles listed as Good articles are being reviewed against the GA criteria as part of the GA project quality task force. While all the hard work that has gone into this article is appreciated, unfortunately, as of February 13, 2008, this article fails to satisfy the criteria, as detailed below. For that reason, the article has been delisted from WP:GA. However, if improvements are made bringing the article up to standards, the article may be nominated at WP:GAN. If you feel this decision has been made in error, you may seek remediation at WP:GAR. GA review – see WP:WIAGA for criteria
I've chosen to delist this article from GA status mostly do to many chunky passages and manual of style infractions. These are listed in detail below.
Detailed comments
-- jwanders Talk 00:05, 13 February 2008 (UTC)
Yup, I'm happy to simply re-instate this. Thanks for all your prompt hard work; first time an article that I've had to delist has received any sort of reply. Kudos! -- jwanders Talk 19:39, 14 February 2008 (UTC)
There is something fundamentally wrong here. As anyone learning to ride a bicycle knows, you can have the easiest, most self-steering bicycle in existence and you will still fall off. After a painful learning process you discover the knack of making small adjustments, and once that becomes a reflex, the experience of riding is just the same as if the bike stays upright on its own.
The way a bike stays upright is by making constant small corrections. I'm not a physicist but dynamic instability is the term that comes to mind - possibly dynamic equilibrium (neither has a Wiki entry that is remotely relevant here). It is highly misleading to suggest that some bikes are self stabilising. Until you get into the realms of powered computer-controlled systems, e.g. Segway, this is simply not true. Yes, a lot of rake increases stability but it does not eliminate the need for corrections.
There is an interesting essay on the subject, here How two bike mechanics taught the human race to fly ProfDEH ( talk) 07:33, 8 May 2008 (UTC)
I've been taking a look at this article with the idea of doing some copy-editing, and I can tell immediately that this will be a real challenge—the article is basically in terrific shape right now. I'll keep looking, though. And perhaps another role I can play here is Sample Layperson. When reading the History section it jumped out at me that it was " Karl von Drais himself" (emphasis is mine). I had to follow the wikilink to find out who he was. Could we add a small phrase, within commas or parentheses, about this notable person (notable not just to science, but to the article at hand as well). I'm not the best person to word this, but it would be something like: "In the early 1800s Karl von Drais, inventor of the velocipede (a bicycle prototype) showed that a rider..." This might be appreciated by your lay readers. -- AnnaFrance ( talk) 18:44, 27 May 2008 (UTC)
In speaking of a bike as an inverted pendulum, the point is made that balancing is easier with a higher center of mass, but that a lower center of mass actually seems easier to the rider when stationary. I gather from this section that balance actually is easier with a lower center of mass when stationary. But then the last sentence says that touring cyclists are advised to carry loads low, i.e., maintain a low center of mass. This confuses me. They would be in motion more of the time, so wouldn't they want to maintain the higher center of mass? Extra note: Isn't it about time to archive this talk page? -- AnnaFrance ( talk) 14:54, 29 May 2008 (UTC)
Do you think it would improve this opening section to take the second paragraph and insert it between the 1st and 2nd sentences of the first? Then you would be introducing the idea of instability, defining the terms stability and instability, and finally introducing the types of instability. Also, I wish something more could be done with the Modes section. It's a section that consists of one line, and much of that is redundant. But it is needed to balance out the Design Criteria section. If you have any free time, you might want to see if there's any way the Modes opening section could be expanded.
Old Business: I like the way you included the second-class lever explanation in the Center of Mass Location section. I think it helps.
Archiving talk page: I've studied up on archiving talk pages, and I think I understand. Let me try it late tonight. That way the activity should be done for the day here, and we can label the archive as being Apr 06 - May 08, starting fresh tomorrow with June 1. -- AnnaFrance ( talk) 19:46, 31 May 2008 (UTC)
This page is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
The comment(s) below were originally left at Talk:Bicycle and motorcycle dynamics/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.
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While I may be biased, because of the work I have done on this article, I gave it an "A" because I believe it meets these criteria:
|
Last edited at 18:40, 1 March 2007 (UTC). Substituted at 14:21, 1 May 2016 (UTC)
Archive 1 has been created with a link at right. Archive 2, when needed in the future, should be a new subpage (same as creating an article) titled "Talk:Bicycle and motorcycle dynamics/Archive 2" and the link added to the template on this page's code. For further information on archiving see Wikipedia:How to archive a talk page. -- AnnaFrance ( talk) 04:24, 1 June 2008 (UTC)
In reference to a change I just made in the sentence:
The "it can be fatal" was originally "they can be fatal". When I made that change, I was assuming that "wobble or shimmy" was referring to 2 words for the same (one, singular) thing. The longer I stare at the sentence, though, the less sure I am that this is what was meant here. Did you mean them to be one thing in this particular sentence, or two?
Old business: I think the opening paragraph of the Instability section works better now (and you eliminated the repetitions). -- AnnaFrance ( talk) 15:56, 2 June 2008 (UTC)
-- AnnaFrance ( talk) 18:33, 5 June 2008 (UTC)
The handlebars issue is a minor one. I've changed the sentenced discussed above. About the bolding: I hear that WP generally discourages bolding outside of titles. Since there are so many sections in this article, it seemed to me that any extra bolding might be seen as screen clutter, so I've taken it all out. -- AnnaFrance ( talk) 19:40, 6 June 2008 (UTC)
In the first paragraph of the Tires section, could we get a brief definition of the term "normal" in parentheses? I think the lay reader can infer the gist of most of the technical terms in this article (contact patch, side slip, etc.), but this one may be a little advanced. -- AnnaFrance ( talk) 20:20, 7 June 2008 (UTC)
I'm going to go back through the article now with an extensive list of WP:MOS guidelines, to try to find any small points missed before. (If anyone would rather that I stop with the nitpicking, please just say so.) One small item that I think would be worth some real effort to get perfect is the opening definition of the article's subject. As a grammatical sentence, I don't think it works all that well:
Bicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles, in entirety or in parts, due to the forces acting on them during balancing, steering, braking, and suspension.
The part that's bothering me is "the forces acting on them during...suspension". That doesn't sound right. Grammatically, it would certainly be best to have a fourth -ing, but "suspending" obviously is ridiculous. Is there a way of referring to all four elements that would be appropriate to all of them? Or am I not interpreting this correctly? -- AnnaFrance ( talk) 17:59, 9 June 2008 (UTC)
While I finish up the final run-through on the text, I'm going to ask my husband, Sfbart ( talk) (who was a professional web developer), to take a look at the image placement. According to the Wikipedia Manual of Style, they prefer the first image to be on the right, then alternate down the page, if possible, to avoid what they call "stackups". We do have a bit of a stackup at one point on the page. I'll ask him to see if he can untangle the stack and alternate sides at least occasionally, without moving any image out of its basic position within the article. -- AnnaFrance ( talk) 22:13, 16 June 2008 (UTC)
In the beginning of this section, one of the features of an idealized bike is:
Could this be changed to:
-- AnnaFrance (talk) 15:20, 19 June 2008 (UTC)
What's next for this article? Try to get a peer review? -- AnnaFrance (talk) 16:27, 20 June 2008 (UTC)
This discussion ( centrifugal force vs inertia) has appeared here before, and has since been archived. As the article on that subject currently states: "Despite the name, fictitious forces are experienced as very real to those actually in a non-inertial frame. Fictitious forces also provide a convenient way to discuss dynamics within rotating environments, and can simplify explanations and mathematics." Centrifugal force provides a simple way to explain leaning in a turn, a convenient way to calculate the lean angle necessary, and so is used in this article.
The current wording; "the external forces are due to gravity, inertia, contact with the ground, and contact with the atmosphere"; does not actually call inertia a force any more than it calls gravity a force. More detail about reference frames is provided just three paragraphs later.- AndrewDressel ( talk) 14:25, 26 June 2008 (UTC)
It appears to me that the capsize speed and the weave speed are reversed, both in the text, in the eigenvalue plot and in the PDF reference [17] by Meijaard, et al. My own experience is that at low speed a bicycle will "capsize" (fall over without any weaves), while at high speed on a poorly designed bicycle the weaves can increase in amplitude until "failure". I'm not an expert, nor a prior contributer to Wikipedia, so I hesitate to make any changes. Comments? —Preceding unsigned comment added by 70.19.235.105 ( talk) 16:41, 13 July 2008 (UTC)
Maybe I missed it in the article, but the main reason for self stability is trail. When the front wheel is leaned, the pavement pushes up (opposing gravity) at the contact patch, and since the contact patch is "behind" the pivot axis (trail), the result is an inwards yaw torque on the front wheel, causing it to steer inwards. Once above some minimum speed, the inwards torque generates enough steering input to result in vertical stability. Note that gyroscopic effects can be eliminated, for example using skates on ice or skis on snow, and "trail effect" would still result in vertical stability. Trail also creates caster effect, which dampens overcorrection due to momentum. Jeffareid ( talk) 01:26, 18 October 2008 (UTC)
To me, terms like stability and riderless bicycles are synonomous with self stability. Note that the Jones article involved real testing of bicycles, not just a paper exercise. Riderless bicycles with negative fork trail fell over almost immediately, riderless bicycles with normal amounts of fork trail were self stable above a minimum speed, riderless bicycles with large amounts of fork trail slowed to a near stop before falling over. I'd call that evidence of a relationship between trail and self-stability.
I'm not claiming that trail is the only source of self-stability, just that it's the main source. Every web article I've found defines a strong correlation between stability and trail, some specifically using the term "self-stability". The fact that trail tends to steer the front tire towards the direction of lean is mentioned in this article. To me, it's this inwards steering reaction that results in self stability. Are you stating that trail has no effect on self stability, in spite of real world experiments that appear to establish a relationship between the amount of trail and the amount of self-stability? Is there some hidden factor I'm missing here? Jeffareid ( talk) 19:35, 18 October 2008 (UTC)