Editing Speed wobble (section)

== In two-wheeled vehicles ==
Wobble or shimmy begins when some otherwise minor irregularity accelerates the wheel to one side. The irregularity may be a wheel which is [[roundness (object)|out-of-round]], out-of-true, or [[tire balance#Dynamic balance|out-of-balance]].{{r |ST}} As the wheel rotates, it will exert a [[oscillation|cyclic]] load to the vehicle frame, which if matched with the system's (vehicle and attached accessories) [[resonance|resonant frequency]], can produce a speed wobble.{{r |ST}} 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 [[steering damper|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.<ref name="Wilson" /> While wobble or shimmy can be easily remedied by adjusting speed, position, or grip on the handlebar, it can be fatal if left uncontrolled.<ref>{{cite news
| title = Crash kills cyclist
| last = Kettler
| first = Bill
|date=2004-09-15
| work = Mail Tribune
| url = http://www.mailtribune.com/article/20040915/BIZ/309159999
| accessdate = 2016-07-10
}}</ref>

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 [[bicycle suspension|suspension system]], and the tire knobs also produce some damping between the vehicle and road interface.{{r |ST |p=1 |q=I&apos;ve seen experts say that increased tire pressure can add stiffness to road tires, but the knobbies on MTB tires don&apos;t subtract stiffness, rather they add damping.}}

Since shimmy frequency is independent of bike speed, gyroscopic effects "are clearly not essential to the phenomenon."<ref name="Wilson" /> 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 force|cornering stiffness]] of the front tire.<ref name="Cossalter"/><ref>{{cite journal
 | author = Manfred Plöchl
 |author2=Johannes Edelmann |author3=Bernhard Angrosch |author4=Christoph Ott
 | title = On the wobble mode of a bicycle
 | journal = Vehicle System Dynamics 
 | volume = 50
 | issue = 3
 | pages = 415–429
 | publisher = Taylor & Francis
 | date = 7 Jul 2011
 | issn = 0042-3114
 | doi=10.1080/00423114.2011.594164|bibcode=2012VSD....50..415P |s2cid=110507657 }}</ref>

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."<ref>{{cite conference |first=Salvador |last=Mauro |author2=Fabris, Davide |title=Study of stability of a two wheeled vehicle through experiments on the road and in laboratory |date=May 27–28, 2004 |location=Modena, Italy |url=http://www.dinamoto.it/dinamoto/7_MDRG_papers/_MDRG%20Papers%20in%20PDF%20format/2004_04%20Study%20of%20stability%20of%20a%20two%20wheeled%20vehicle%20MODENA.pdf |accessdate=2008-08-31}}</ref>