Talk:Speed wobble

Single pivot point

I wonder if speed wobbles would apply to any vehicle with single front pivot point. Reflex Action (Apr 2005)

Speed Wobble

We can have articles link here, but lets not pretend that "Speed wobble" is a popularly used term (unless it is?) AdamBiswanger1 03:32, 14 July 2006 (UTC)

Speed wobble in cars?

The article says: It can occur with motorcycles, skateboards, bicycles or in theory any vehicle with a single steering pivot point and a sufficient amount of freedom of the steered wheel; this does not include automobiles..

Googling for 'shimmy death-wobble' will produce plenty of webpages describing similar things in cars. Also the article Hunting (engineering) mentions this. So why this remark? -- Han-Kwang 11:08, 15 July 2006 (UTC)

Nutation requires 2 degrees of freedom orthogonal to the spin axis. Car wheels do not have this freedom. Jurien 01:07, 17 July 2006 (UTC)

In theory cars may not have such degree of freedom, but in practice steering and suspension components are not indefinitely rigid, due to the use of elastic bushings. Additionally wear and tear may introducer play in the system. A "death wobble" in a car or more commonly in a truck may occur when steering components e.g. steering box remain rigid, but knuckles are allowed to rotate left and right a bit, sufficient to steer the wheels. Then an oscillation may occur due to the wheels steering in one direction and then due to the force from tires flexing the system turning to the other direction, which in turn causes knuckle to rotate back and cycle continues. Mibars (talk) 15:00, 24 February 2021 (UTC)

Death wobble vs. shimmy?

It's not clear from the article what the difference is between a death wobble and a shimmy. Han-Kwang 11:08, 15 July 2006 (UTC)

Thanks for the feedback, I'll make it clearer. Jurien 01:07, 17 July 2006 (UTC)

When I wrote my comment I didn't realize that you were in the middle of a rewrite. I saw today after you bolded various phrases that it was already there, just not under the heading Shimmy and death wobble where I expected it. I'm not confident to change the article without introducing errors, but I suggest that you start the section Shimmy and death wobble by explaining in simple language what the difference between the two is, preferably without technical terms such as gimbal, nutation, and pivot. After that you can go into more detail. I must say though that I find it hard to follow the article despite a PhD degree in (chemical) physics. A simple picture of the two cases would help tremendously, for example with a front view of the bike and a top view, with in two different colors the different extreme orientations of the bike plus its rider. Han-Kwang 13:46, 17 July 2006 (UTC)

Good idea. This wiki entry is very much under development.--Jurien 04:35, 18 July 2006 (UTC)

An Inaccuracy.

In the article, you write, "In 2002 Harley-Davidson was sued in a class action suit for injuries associated with high speed wobbles, also known as "tank slappers" because of the tendency of handle bars to move towards the tank." Are you sure? Because I am pretty sure that is not true. If you do not have facts to back that up, I would remove that statement from the article.

I'll put a on it AdamBiswanger1 14:56, 10 August 2006 (UTC)

Since there has been no citation added and it has been over a week, can I rightfully remove that sentence from the article?

No objections from me AdamBiswanger1 18:40, 17 August 2006 (UTC)

Cleanup

This article is difficult to read, poorly worded in some cases, and is not clear to someone unfamiliar with the subject. Also, I think that it goes too in-depth for one article, as it should be a summary, not an in-depth article. Maybe putting the two primary sections into separate articles? Jenrzzz (talk) 06:39, 12 December 2007 (UTC)

This article needs serious attention. — Preceding unsigned comment added by LanceFortier (talk • contribs) 03:01, 16 November 2018 (UTC)

Original research?

Neither Wilson in Bicycling Science nor Cossalter in Motorcycle Dynamics distinguish between wobble and shimmy, although they both discuss one or the other at length. Nor do either mention nutation as being a facter in either phenomona.

I don't see a single reference in the entire article. Perhaps I missed them. Is this just all original research? -AndrewDressel (talk) 02:14, 2 May 2008 (UTC)

There is a great deal of valuable information here, and most of it seems to be about right. Yes, the article could be cleaned up to some extent in terms of consistent terminology (death wobble, speed wobble, etc.) The solution to the lack of sources is not to delete the content, but to find the sources. A decent college text book on dynamics would be the place to start. Paulgush (talk) 08:14, 11 May 2008 (UTC)

I'm not sure what exactly you mean by "decent college text book on dynamics". Certainly none of the popular introductory texts, such as Hibbeler, Beer & Johnston, or Bedford & Fowler, mention shimmy. They barely touch on nutation. More advanced texts, including Greenwood, Goldstein, and Kane & Levinson, go into a lot more detail on nutation, but none link it to shimmy. Greenwood even follows up discussion of top nutation with a rolling disk example, but never mentions nutation of the disk. These are all arguably pretty decent text books. -AndrewDressel (talk) 17:11, 11 May 2008 (UTC)

Watch the video link at the bottom of the article. The handlebars (inner gimbal) are oscillating at the same frequency as the motorcycle itself (outer gimbal). This is clearly nutation of the front wheel. Paulgush (talk) 08:23, 11 May 2008 (UTC)

There is a lot going on in the video that is impossible to see: the rider may be applying torque to the steering mechanism, the front and rear tires are flexing and interacting with the pavement, the front and rear suspensions are reacting to the motion of the frame, the frame and fork may be flexing, etc. In fact, Cossalter, who heads the Motorcycle Dynamics Research Group at Padua University Italy, in Motorcycle Dynamics, Second Edition, on page 272, lists the top 5 influences on wobble to be lateral stiffness of the front tire, steering damper, height of bike center of mass, distance of bike center of mass from rear wheel, and cornering stiffness of the front tire. Simply noting that the handlebars are oscillating at the same frequency as the motorcycle itself, and declaring this to be nutation is not a reference. Interestingly, the single other external link given, to an article by Jobst Brandt on Sheldon Brown's web site, also does not mention nutation.

Further, in a paper titled Study of stability of a two wheeled vehicle through experiments on the road and in laboratory presented at “AUTOMOBILI E MOTORI HIGH - TECH” MODENA, 27-28th MAY 2004 and available online at http://www.dinamoto.it/ by Mauro Salvador, Davide Fabris of the MDRG at Padua University, that investigates wobble through physical experimentation and computer modeling, they conclude "the influence on wobble mode of front tyre characteristics, front frame inertia and chassis stiffness were shown. In particular, it shows that increasing front tire inflation, stiffness chassis, and front frame inertia about steering axis and decreasing sideslip stiffness of front tire, wobble mode damping is improved, promoting vehicle stability." No mention of front wheel nutation at all.

In fact, Wilson and Papadopoulos, in Bicycling Science, Third Edition, on page 292-296, use the argument that since shimmy frequency is independent of bike speed, gyroscopic effects "are clearly not essential to the phenomenon." Papadopoulos is also co-author of Linearized dynamics equations for the balance and steer of a bicycle: a benchmark and review, recently published in Proc. Roy. Soc. A., Volume 463, Number 2084 / August 08, 2007, pages 1955-1982. DOI 10.1098/rspa.2007.1857.

I am beginning to suspect that the article as it currently exists does not cite any references because there are none to cite. Wikipedia is quite clear about the need to cite sources and the prohibition of original research. -AndrewDressel (talk) 17:11, 11 May 2008 (UTC)

Wobble vs tank slapper

The objection has been raised that

a tank-slapper is something completely different (kickback) and has completely different causes; it has nothing to do with oscillation or resonance. -Cancun771 08:03, 28 December 2009

I'm away from my desk and so do not have my texts, but I can find online [this article] from Tony Foale that suggests strongly to me that a tank slapper is merely a highly developed wobble:

This really matters, because wobbles can be caused or greatly increased by this misalignment... We have all experienced this to some degree, sometimes it amounts to nothing more than a minor handle bar shake, but in far too many cases it can develop into a frightening tank slapper with occasional fatal results.

Are there other sources that support or refute this claim? -AndrewDressel (talk) 18:54, 27 December 2009 (UTC)

• Hough, David L. (2000), "Glossary", Proficient Motorcycling: The Ultimate Guide to Riding Well (2nd ed.), USA: BowTie Press, p. 253, ISBN 1889540536, tank slapper: a speed wobble so severe that the handlebars bang alternately against the sides of the fuel tank

  See also: [23], [24], [25], [26]

  Unfortunately, some people edit Wikipedia as if it were Urban Dictionary where you can just throw in whatever you heard your friend say. --Dbratland (talk) 19:17, 27 December 2009 (UTC)