Open main menu
Home
Random
Recent changes
Special pages
Community portal
Preferences
About Wikipedia
Disclaimers
Incubator escapee wiki
Search
User menu
Talk
Dark mode
Contributions
Create account
Log in
Editing
Countersteering
(section)
Warning:
You are not logged in. Your IP address will be publicly visible if you make any edits. If you
log in
or
create an account
, your edits will be attributed to your username, along with other benefits.
Anti-spam check. Do
not
fill this in!
==How it works== [[File:Countersteering with scooter - Montage of four images.png|thumb|right|Image montage showing different stages of countersteering. Here, a scooter is countersteered to turn left.]] When countersteering to turn right, the following is performed:<ref>{{cite web | url = http://www.phys.lsu.edu/faculty/gonzalez/Teaching/Phys7221/vol59no9p51_56.pdf | first = David | last = Jones | title = The Stability of the Bicycle | year = 1970 | access-date = 31 March 2009}}</ref><ref name=CW1985>{{citation | title=More on countersteering | journal=Cycle World | date=October 1985 | page=71 | url=https://books.google.com/books?id=KEtpOie7PjkC&pg=RA11-PA71 | quote=[A] motorcycle has to lean to turn, and countersteering to the left steers the front wheel out from under the motorcycle, causing the motorcycle to lean to the right. So the basic sequence for the right turn is this: turn the bars to the left to start the turn, and then let them swing back to the right as you settle into a steady cornering attitude. Many (if not most) motorcyclists are not consciously aware of this sequence, and find it slightly incredible... [but] it is the only way to make a motorcycle turn quickly.}}</ref> * A torque on the handlebars to the left is applied. * The front wheel will then rotate about the steering axis to the left and the tire will generate forces in the contact patch to the left. * The machine as a whole steers to the left. * Because the forces in the contact patch are at ground level, this pulls the wheels "out from under" the bike to the left and causes it to lean to the right. * The rider, or in most cases the inherent stability of the bike, provides the steering torque necessary to rotate the front wheel back to the right and in the direction of the desired turn. * The bike begins a turn to the right. While this appears to be a complex sequence of motions, it is performed by every child who rides a bicycle. The entire sequence goes largely unnoticed by most riders, which is why some assert that they do not do it.<ref name=CW1985/> It is also important to distinguish the steering torque necessary to initiate the lean required for a given turn from the sustained steering torque and steering angle necessary to maintain a constant radius and lean angle until it is time to exit the turn. * The initial steer torque and angle are both opposite the desired turn direction. * The sustained steer angle is in the same direction as the turn. * The sustained steer torque required to maintain that steer angle is either with or opposite the turn<ref name="Cossalter-p.1343">V. Cossalter pp. 1343β1356: "Correlations with the subjective opinions of expert test riders have shown that a low torque effort should be applied to the handlebar in order to have a good feeling, and preferably in a sense opposite to the turning direction."</ref> direction depending on forward speed, bike geometry, and combined bike and rider mass distribution. ===Need to lean to turn=== A bike can negotiate a curve only when the combined [[center of mass]] of bike and rider leans toward the inside of the turn at an angle appropriate for the velocity and the radius of the turn: :<math>\theta = \arctan \left (\frac{v^2}{gr}\right )</math> where <math>v</math> is the forward speed, <math>r</math> is the radius of the turn and <math>g</math> is the acceleration of [[gravity]].<ref name="fajans" /> Higher speeds and tighter turns require greater lean angles. If the mass is not first leaned into the turn, the [[inertia]] of the rider and bike will cause them to continue in a straight line as the tires track out from under them along the curve. The transition of riding in a straight line to negotiating a turn is a process of leaning the bike into the turn, and the most practical way to cause that lean (of the combined center of mass of bike and rider) is to move the support points in the opposite direction first.<ref name="Wilson">{{cite book | title = Bicycling Science | edition = Third | last = Wilson | first = David Gordon | author2 = Jim Papadopoulos | year = 2004 | publisher = The MIT Press | isbn = 0-262-73154-1 | pages = [https://archive.org/details/isbn_9780262731546/page/270 270β272] | url = https://archive.org/details/isbn_9780262731546/page/270 }}</ref> ===Stable lean=== [[Image:Countersteer response.JPG|thumb|290px|Graphs showing the lean and steer angle response of an otherwise uncontrolled simplified model of a typical bike, traveling at a forward speed in its [[Bicycle and motorcycle dynamics#Self-stability|stable range]] (in this case 6 m/s), to a positive steer torque (to the right) that begins as an impulse and then remains constant. It causes an initial steer angle to the right, a lean to the left, and eventually a steady-state lean to the left, steer angle to the left, and thus a turn to the left.]] As the desired angle is approached, the front wheel must usually be steered into the turn to maintain that angle or the bike will continue to lean with gravity, increasing in rate, until the side contacts the ground. This process often requires little or no physical effort, because the [[Bicycle and motorcycle geometry|geometry of the steering system of most bikes]] is designed in such a way that the front wheel has a strong tendency to steer in the direction of a lean. The actual torque the rider must apply to the handlebars to maintain a steady-state turn is a complex function of bike geometry, mass distribution, rider position, tire properties, turn radius, and forward speed. At low speeds, the steering torque necessary from the rider is usually negative, that is opposite the direction of the turn, even when the steering angle is in the direction of the turn. At higher speeds, the direction of the necessary input torque often becomes positive, that is in the same direction as the turn.<ref name="Cossalter-p.1343" /><ref name="Cossalter">V. Cossalter pp. 241β342</ref> ===At low speeds=== At low speeds countersteering is equally necessary, but the countersteering is then so subtle that it is hidden by the continuous corrections that are made in balancing the bike, often falling below a [[just noticeable difference]] or threshold of perception of the rider. Countersteering at low speed may be further concealed by the ensuing much larger steering angle possible in the direction of the turn.{{citation needed|date=July 2014}} ===Gyroscopic effects=== One effect of turning the front wheel is a roll [[Moment (physics)|moment]] caused by gyroscopic [[precession]]. The magnitude of this moment is proportional to the [[moment of inertia]] of the front wheel, its spin rate (forward motion), the rate that the rider turns the front wheel by applying a torque to the handlebars, and the [[Trigonometric function#cosine|cosine]] of the angle between the steering axis and the vertical.<ref name="Cossalter" /> For a sample motorcycle moving at 22 m/s (50 mph) that has a front wheel with a moment of inertia of 0.6 kgm<sup>2</sup>, turning the front wheel one degree in half a second generates a roll moment of 3.5 Nm. In comparison, the lateral force on the front tire as it tracks out from under the motorcycle reaches a maximum of 50 N. This, acting on the 0.6 m (2 ft) height of the center of mass, generates a roll moment of 30 Nm.<ref name="Cossalter" /> While the moment from gyroscopic forces is only 12% of this, it can play a significant part because it begins to act as soon as the rider applies the torque, instead of building up more slowly as the wheel out-tracks. This can be especially helpful in [[motorcycle racing]].<ref name="Cossalter"/>
Edit summary
(Briefly describe your changes)
By publishing changes, you agree to the
Terms of Use
, and you irrevocably agree to release your contribution under the
CC BY-SA 4.0 License
and the
GFDL
. You agree that a hyperlink or URL is sufficient attribution under the Creative Commons license.
Cancel
Editing help
(opens in new window)