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Speed wobble

January 01, 1970

Wobble, shimmy, tank-slapper,[1] speed wobble, and even death wobble are all words and phrases used to describe a quick (4–10 Hz) oscillation of primarily just the steerable wheel(s) of a vehicle. Initially, the rest of the vehicle remains mostly unaffected, until translated into a vehicle yaw oscillation of increasing amplitude producing loss of control. Vehicles that can experience this oscillation include motorcycles and bicycles, skateboards, and, in theory, any vehicle with a single steering pivot point and a sufficient amount of freedom of the steered wheel, including that which exists on some light aircraft with tricycle gear where instability can occur at speeds of less than 80 km/h (50 mph); this does not include most automobiles. The initial instability occurs mostly at high speed and is similar to that experienced by shopping cart wheels and aircraft landing gear.[2][3]

Theory edit

Sustained oscillation has two necessary components: an underdamped second- or higher-order system and a positive feedback mechanism. An example of an underdamped second order system is a spring–mass system, where the mass can bob up and down (oscillate) when hanging from a spring.

If shimmy cannot be designed out of the system, a device known as a steering damper may be used, which is essentially a notch filter designed to damp the shimmy at its known natural frequency.[4]

Shimmy is usually associated with the deformation of (rubber) tires. However, it can also be observed in nondeformable (e.g., steel) wheels. The phenomenon can be explained by introducing multicomponent dry friction forces,[5] apart from the usual forces considered in the literature.

Another explanation is that speed wobble is a Hopf bifurcation, whereby a system changes from one state (a stable ride) to a second state, (constant amplitude oscillation), when one parameter (forward speed, or air speed) progresses through a critical point. [6]: 1  [7]: 1 

In two-wheeled vehicles edit

Wobble or shimmy begins when some otherwise minor irregularity accelerates the wheel to one side. The irregularity may be a wheel which is out-of-round, out-of-true, or out-of-balance.[6] As the wheel rotates, it will exert a cyclic load to the vehicle frame, which if matched with the system's (vehicle and attached accessories) resonant frequency, can produce a speed wobble.[6] During the wheel rotation, a restoring force is applied in phase with the progress of the irregularity, and the wheel turns to the other side where the process is repeated. If there is insufficient damping in the steering the oscillation will increase until system failure. The oscillation frequency can be changed by changing the forward speed, making the bike stiffer or lighter, or increasing the stiffness of the steering, of which the rider is a main component.[2] While wobble or shimmy can be easily remedied by adjusting speed, position, or grip on the handlebar, it can be fatal if left uncontrolled.[8]

Other things being equal, speed wobble is generally less likely to occur in a mountain bike compared to a road bike, because a mountain bike's frame generally has more damping from the suspension system, and the tire knobs also produce some dampening between the vehicle and road interface.[6]: 1 

Since shimmy frequency is independent of bike speed, gyroscopic effects "are clearly not essential to the phenomenon."[2] The top five influences on wobble have been found 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.[3][9]

An academic paper that investigated wobble through physical experimentation and computer modeling concludes: "the influence on wobble mode of front tire characteristics, front frame inertia and chassis stiffness were shown. In particular, it shows that [by] increasing front tire inflation, chassis stiffness, and front frame inertia about steering axis and decreasing sideslip stiffness of front tire, wobble mode damping is improved, promoting vehicle stability."[10]

In single-wheeled mobility devices edit

Speed wobbles occur on Electric unicycles (EUC) and single-wheeled skateboards (such as a Onewheel). "To fix Onewheel wobbles, both feet need to be repositioned by inching them to a position that properly provides a center of gravity. The Onewheel’s controller is designed to only balance the board from front-to-back having no control of the side-to-side movement."[11]

See also edit

References edit

  1. ^ Hough, David L. (2000). "Glossary". Proficient Motorcycling: The Ultimate Guide to Riding Well (2nd ed.). USA: BowTie Press. p. 253. ISBN 1-889540-53-6. tank slapper: a speed wobble so severe that the handlebars bang alternately against the sides of the fuel tank
  2. ^ a b c Wilson, David Gordon; Jim Papadopoulos (2004). Bicycling Science (Third ed.). The MIT Press. pp. 263–390. ISBN 0-262-73154-1.
  3. ^ a b Cossalter, Vittore (2006). Motorcycle Dynamics (Second ed.). Lulu.com. pp. 241–342. ISBN 978-1-4303-0861-4.
  4. ^ Simos Evangelou, David J.N. Limebeer, Robin S. Sharp, and Malcolm C. Smith (October 2006). "Control of Motorcycle Steering Instabilities". IEEE Control Systems Magazine. CiteSeerX 10.1.1.227.9657. For machines with a stiff front frame, a steering damper is required to stabilize the wobble mode at high speeds, while older, more flexible machines may require a steering damper at intermediate speeds.{{cite magazine}}: CS1 maint: multiple names: authors list (link)
  5. ^ Zhuravlev, V.Ph.; Klimov, D.M. (2010). "Theory of the shimmy phenomenon". Mechanics of Solids. 4 (3): 324–330. Bibcode:2010MeSol..45..324Z. doi:10.3103/S0025654410030039. S2CID 122904947.
  6. ^ a b c d Empfield, Dan (2015-04-24). "Speed Wobble". slowtwitch.com. from the original on 2015-06-07. Retrieved 2019-08-23.
  7. ^ Zinn, Lennard (2013-11-19). "Technical FAQ: Bifurcation and high-speed shimmy". VeloNews. from the original on 2019-08-24. Retrieved 2019-08-23.
  8. ^ Kettler, Bill (2004-09-15). "Crash kills cyclist". Mail Tribune. Retrieved 2016-07-10.
  9. ^ Manfred Plöchl; Johannes Edelmann; Bernhard Angrosch; Christoph Ott (7 Jul 2011). "On the wobble mode of a bicycle". Vehicle System Dynamics. 50 (3). Taylor & Francis: 415–429. Bibcode:2012VSD....50..415P. doi:10.1080/00423114.2011.594164. ISSN 0042-3114. S2CID 110507657.
  10. ^ Mauro, Salvador; Fabris, Davide (May 27–28, 2004). Study of stability of a two wheeled vehicle through experiments on the road and in laboratory (PDF). Modena, Italy. Retrieved 2008-08-31.
  11. ^ "Onewheel Wobbles & Feels Unstable [How-to Fix the Wobbling]". Trailwheel. 7 October 2022.

External links edit

  • Bicycle speed wobbles
  • [Flash] video of motorcycle+rider crashing due to a death wobble
  • Animation of shimmy
  • Animation of death wobble
  • Video of a high-speed streamlined bicycle crash showing death wobble
  • Video of a truck with death wobble

January 01, 1970
speed, wobble, this, article, technical, most, readers, understand, please, help, improve, make, understandable, experts, without, removing, technical, details, march, 2020, learn, when, remove, this, message, wobble, shimmy, tank, slapper, speed, wobble, even. This article may be too technical for most readers to understand Please help improve it to make it understandable to non experts without removing the technical details March 2020 Learn how and when to remove this message Wobble shimmy tank slapper 1 speed wobble and even death wobble are all words and phrases used to describe a quick 4 10 Hz oscillation of primarily just the steerable wheel s of a vehicle Initially the rest of the vehicle remains mostly unaffected until translated into a vehicle yaw oscillation of increasing amplitude producing loss of control Vehicles that can experience this oscillation include motorcycles and bicycles skateboards and in theory any vehicle with a single steering pivot point and a sufficient amount of freedom of the steered wheel including that which exists on some light aircraft with tricycle gear where instability can occur at speeds of less than 80 km h 50 mph this does not include most automobiles The initial instability occurs mostly at high speed and is similar to that experienced by shopping cart wheels and aircraft landing gear 2 3 Contents 1 Theory 2 In two wheeled vehicles 3 In single wheeled mobility devices 4 See also 5 References 6 External linksTheory editSustained oscillation has two necessary components an underdamped second or higher order system and a positive feedback mechanism An example of an underdamped second order system is a spring mass system where the mass can bob up and down oscillate when hanging from a spring If shimmy cannot be designed out of the system a device known as a steering damper may be used which is essentially a notch filter designed to damp the shimmy at its known natural frequency 4 Shimmy is usually associated with the deformation of rubber tires However it can also be observed in nondeformable e g steel wheels The phenomenon can be explained by introducing multicomponent dry friction forces 5 apart from the usual forces considered in the literature Another explanation is that speed wobble is a Hopf bifurcation whereby a system changes from one state a stable ride to a second state constant amplitude oscillation when one parameter forward speed or air speed progresses through a critical point 6 1 7 1 In two wheeled vehicles editWobble or shimmy begins when some otherwise minor irregularity accelerates the wheel to one side The irregularity may be a wheel which is out of round out of true or out of balance 6 As the wheel rotates it will exert a cyclic load to the vehicle frame which if matched with the system s vehicle and attached accessories resonant frequency can produce a speed wobble 6 During the wheel rotation a restoring force is applied in phase with the progress of the irregularity and the wheel turns to the other side where the process is repeated If there is insufficient damping in the steering the oscillation will increase until system failure The oscillation frequency can be changed by changing the forward speed making the bike stiffer or lighter or increasing the stiffness of the steering of which the rider is a main component 2 While wobble or shimmy can be easily remedied by adjusting speed position or grip on the handlebar it can be fatal if left uncontrolled 8 Other things being equal speed wobble is generally less likely to occur in a mountain bike compared to a road bike because a mountain bike s frame generally has more damping from the suspension system and the tire knobs also produce some dampening between the vehicle and road interface 6 1 Since shimmy frequency is independent of bike speed gyroscopic effects are clearly not essential to the phenomenon 2 The top five influences on wobble have been found 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 3 9 An academic paper that investigated wobble through physical experimentation and computer modeling concludes the influence on wobble mode of front tire characteristics front frame inertia and chassis stiffness were shown In particular it shows that by increasing front tire inflation chassis stiffness and front frame inertia about steering axis and decreasing sideslip stiffness of front tire wobble mode damping is improved promoting vehicle stability 10 In single wheeled mobility devices editSpeed wobbles occur on Electric unicycles EUC and single wheeled skateboards such as a Onewheel To fix Onewheel wobbles both feet need to be repositioned by inching them to a position that properly provides a center of gravity The Onewheel s controller is designed to only balance the board from front to back having no control of the side to side movement 11 See also editBicycle and motorcycle dynamics Caster flutter Fishtailing Hunting oscillation Pilot induced oscillation Self oscillation Tire balance Trailer vehicle Vehicle dynamicsReferences edit Hough David L 2000 Glossary Proficient Motorcycling The Ultimate Guide to Riding Well 2nd ed USA BowTie Press p 253 ISBN 1 889540 53 6 tank slapper a speed wobble so severe that the handlebars bang alternately against the sides of the fuel tank a b c Wilson David Gordon Jim Papadopoulos 2004 Bicycling Science Third ed The MIT Press pp 263 390 ISBN 0 262 73154 1 a b Cossalter Vittore 2006 Motorcycle Dynamics Second ed Lulu com pp 241 342 ISBN 978 1 4303 0861 4 Simos Evangelou David J N Limebeer Robin S Sharp and Malcolm C Smith October 2006 Control of Motorcycle Steering Instabilities IEEE Control Systems Magazine CiteSeerX 10 1 1 227 9657 For machines with a stiff front frame a steering damper is required to stabilize the wobble mode at high speeds while older more flexible machines may require a steering damper at intermediate speeds a href Template Cite magazine html title Template Cite magazine cite magazine a CS1 maint multiple names authors list link Zhuravlev V Ph Klimov D M 2010 Theory of the shimmy phenomenon Mechanics of Solids 4 3 324 330 Bibcode 2010MeSol 45 324Z doi 10 3103 S0025654410030039 S2CID 122904947 a b c d Empfield Dan 2015 04 24 Speed Wobble slowtwitch com Archived from the original on 2015 06 07 Retrieved 2019 08 23 Zinn Lennard 2013 11 19 Technical FAQ Bifurcation and high speed shimmy VeloNews Archived from the original on 2019 08 24 Retrieved 2019 08 23 Kettler Bill 2004 09 15 Crash kills cyclist Mail Tribune Retrieved 2016 07 10 Manfred Plochl Johannes Edelmann Bernhard Angrosch Christoph Ott 7 Jul 2011 On the wobble mode of a bicycle Vehicle System Dynamics 50 3 Taylor amp Francis 415 429 Bibcode 2012VSD 50 415P doi 10 1080 00423114 2011 594164 ISSN 0042 3114 S2CID 110507657 Mauro Salvador Fabris Davide May 27 28 2004 Study of stability of a two wheeled vehicle through experiments on the road and in laboratory PDF Modena Italy Retrieved 2008 08 31 Onewheel Wobbles amp Feels Unstable How to Fix the Wobbling Trailwheel 7 October 2022 External links editBicycle speed wobbles Flash video of motorcycle rider crashing due to a death wobble Animation of shimmy Animation of death wobble Video of a high speed streamlined bicycle crash showing death wobble Video of a truck with death wobble Retrieved from https en wikipedia org w index php title Speed wobble amp oldid 1219706069, wikipedia, wiki, book, books, library,

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