Camber thrust

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Camber thrust and camber force are terms used to describe the force generated perpendicular to the direction of travel of a rolling tire due to its camber angle and finite contact patch. [1] [2] [3] Camber thrust is generated when a point on the outer surface of a leaned and rotating tire, that would normally follow a path that is elliptical when projected onto the ground, is forced to follow a straight path while coming in contact with the ground, due to friction. This deviation towards the direction of the lean causes a deformation in the tire tread and carcass that is transmitted to the vehicle as a force in the direction of the lean. [2]

Tire ring-shaped covering that fits around a wheels rim

A tire or tyre is a ring-shaped component that surrounds a wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide traction on the surface traveled over. Most tires, such as those for automobiles and bicycles, are pneumatically inflated structures, which also provide a flexible cushion that absorbs shock as the tire rolls over rough features on the surface. Tires provide a footprint that is designed to match the weight of the vehicle with the bearing strength of the surface that it rolls over by providing a bearing pressure that will not deform the surface excessively.

Camber angle

Camber angle is the angle made by the wheels of a vehicle; specifically, it is the angle between the vertical axis of the wheels used for steering and the vertical axis of the vehicle when viewed from the front or rear. It is used in the design of steering and suspension. If the top of the wheel is farther out than the bottom, it is called positive camber; if the bottom of the wheel is farther out than the top, it is called negative camber.

Contact patch the portion of a tire that is in contact with the surface

Contact patch is the portion of a vehicle's tire that is in actual contact with the road surface. It is commonly used in the discussion of pneumatic tires, where the term is used strictly to describe the portion of the tire’s tread that touches the road surface. The term “footprint” is used almost synonymously. Solid wheels also exhibit a contact patch which is generally smaller than the pneumatic “footprint”.

Contents

Camber thrust is approximately linearly proportional to camber angle for small angles, [2] [4] reaches its steady-state value nearly instantaneously after a change in camber angle, and so does not have an associated relaxation length. Bias-ply tires have been found to generate more camber thrust than radial tires. [3] Camber stiffness is a parameter used to describe the camber thrust generated by a tire and it is influenced by inflation pressure and normal load. [3] The net camber thrust is usually in front of the center of the wheel and so generates a camber torque, twisting torque, or twisting moment. [3] The orientation of this torque is such that it tends to steer a tire towards the direction that it is leaned. An alternate explanation for this torque is that the two sides of the contact patch are at different radii from the axle and so would travel forward at different rates unless constrained by friction with the pavement. [2]

Relaxation length

Relaxation length is a property of pneumatic tires that describes the delay between when a slip angle is introduced and when the cornering force reaches its steady-state value. It is also described as the distance that a tire rolls before the lateral force builds up to 63% of its steady-state value. It can be calculated as the ratio of cornering stiffness over the lateral stiffness, where cornering stiffness is the ratio of cornering force over slip angle, and lateral stiffness is the ratio of lateral force over lateral displacement.

On bikes

On bicycles and motorcycles, camber thrust contributes to the centripetal force necessary to cause the vehicle to deviate from a straight path, along with cornering force due to the slip angle, can be the largest contributor, [1] and in some cases is the sole contributor. [2] Camber thrust contributes to the ability of bikes to negotiate a turn with the same radius as automobiles but with a smaller steering angle. [1] When a bike is steered and leaned in the same direction, the camber angle of the front tire is greater than that of the rear and so can generate more camber thrust, all else being equal. [2]

Bicycle pedal-driven two-wheel vehicle

A bicycle, also called a cycle or bike, is a human-powered or motor-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A bicycle rider is called a cyclist, or bicyclist.

Motorcycle two- or three-wheeled motor vehicle

A motorcycle, often called a bike, motorbike, or cycle, is a two- or three-wheeled motor vehicle. Motorcycle design varies greatly to suit a range of different purposes: long distance travel, commuting, cruising, sport including racing, and off-road riding. Motorcycling is riding a motorcycle and related social activity such as joining a motorcycle club and attending motorcycle rallies.

A centripetal force is a force that makes a body follow a curved path. Its direction is always orthogonal to the motion of the body and towards the fixed point of the instantaneous center of curvature of the path. Isaac Newton described it as "a force by which bodies are drawn or impelled, or in any way tend, towards a point as to a centre". In Newtonian mechanics, gravity provides the centripetal force responsible for astronomical orbits.

On automobiles

On automobiles, camber thrust may contribute to or subtract from the total centripetal force generated by the tire, depending on the camber angle. On a well-aligned vehicle, camber thrust from the tires on each side balances out. [5] On a surface rough enough for one front tire to momentarily lose traction, camber thrust from the other front tire can cause the vehicle to wander or feel skittish. [5]

See also

Bicycle and motorcycle dynamics

Bicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles and their components, due to the forces acting on them. Dynamics falls under a branch of physics known as classical mechanics. Bike motions of interest include balancing, steering, braking, accelerating, suspension activation, and vibration. The study of these motions began in the late 19th century and continues today.

Cornering force

Cornering force or side force is the lateral force produced by a vehicle tire during cornering.

For vehicles such as cars, vehicle dynamics is the study of how the vehicle will react to driver inputs on a given road.

Related Research Articles

Circle of forces

The circle of forces, traction circle, friction circle, or friction ellipse is a useful way to think about the dynamic interaction between a vehicle's tire and the road surface. The diagram below shows the tire from above, so that the road surface lies in the x-y plane. The vehicle to which the tire is attached is moving in the positive y direction.

Slip angle

In vehicle dynamics, slip angle or sideslip angle is the angle between the direction in which a wheel is pointing and the direction in which it is actually traveling. This slip angle results in a force, the cornering force, which is in the plane of the contact patch and perpendicular to the intersection of the contact patch and the midplane of the wheel. This cornering force increases approximately linearly for the first few degrees of slip angle, then increases non-linearly to a maximum before beginning to decrease.

Understeer and oversteer

Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Oversteer is what occurs when a car turns (steers) by more than the amount commanded by the driver. Conversely, understeer is what occurs when a car steers less than the amount commanded by the driver.

Automobile handling and vehicle handling are descriptions of the way a wheeled vehicle responds and reacts to the inputs of a driver, as well as how it moves along a track or road. It is commonly judged by how a vehicle performs particularly during cornering, acceleration, and braking as well as on the vehicle's directional stability when moving in steady state condition.

A highsider or highside is a type of motorcycle accident characterized by sudden and violent rotation of the bike around its long axis. This generally happens when the rear wheel loses traction, skids, and then suddenly regains traction, creating a large torque which flips the rider head first off the side of the motorcycle or over the handlebars.

The lowsider or lowside is a type of motorcycle or bicycle crash usually occurring in a turn. It is caused when either the front or rear wheel slides out as a result of either too much braking into the corner, too much acceleration through or out of the corner, or too much speed carried into or through the corner for the available grip. It may also be caused by unexpected slippery or loose material on the road surface.

Caster angle

The caster angle or castor angle is the angular displacement of the steering axis from the vertical axis of a steered wheel in a car, motorcycle, bicycle, other vehicle or a vessel, measured in the longitudinal direction. It is the angle between the pivot line and vertical. In automobile racing, the caster angle may be adjusted to optimize handling characteristics for a particular venue.

Countersteering

Countersteering is used by single-track vehicle operators, such as cyclists and motorcyclists, to initiate a turn toward a given direction by momentarily steering counter to the desired direction. To negotiate a turn successfully, the combined center of mass of the rider and the single-track vehicle must first be leaned in the direction of the turn, and steering briefly in the opposite direction causes that lean. The rider's action of countersteering is sometimes referred to as "giving a steering command".

Tilting three-wheeler

A tilting three-wheeler, or tilting trike is a three-wheeled vehicle whose body and or wheels tilt in the direction of a turn, and is usually a narrow-track vehicle. Such vehicles can corner without rolling over despite having a narrow track because they can balance some or all of the tipping moment caused by centripetal acceleration with an opposite tipping moment caused by gravity, as bicycles and motorcycles do. This also reduces the lateral acceleration experienced by the rider, which some find more comfortable than the alternative. The narrow profile can result in reduced aerodynamic drag and increased fuel efficiency. These types of vehicles have also been described as "man-wide vehicles" (MWV).

Trail braking

Trail braking is a driving and motorcycle riding technique where the brakes are used beyond the entrance to a turn, and then gradually released up to, or before, the apex of the turn.

A Bundorf analysis is a measure of the characteristics of a vehicle that govern its understeer balance. The understeer is measured in units of degrees of additional yaw per g of lateral acceleration.

Bicycle and motorcycle geometry

Bicycle and motorcycle geometry is the collection of key measurements that define a particular bike configuration. Primary among these are wheelbase, steering axis angle, fork offset, and trail. These parameters have a major influence on how a bike handles.

The scrub radius is the distance in front view between the king pin axis and the center of the contact patch of the wheel, where both would theoretically touch the road.

Self aligning torque

Self aligning torque, also known as aligning torque, aligning moment, SAT, or Mz, is the torque that a tire creates as it rolls along, which tends to steer it, i.e. rotate it around its vertical axis. In the presence of a non-zero slip angle, this torque tends to steer the tire toward the direction in which it is traveling, hence its name.

Pneumatic trail

Pneumatic trail or trail of the tire is a trail-like effect generated by compliant tires rolling on a hard surface and subject to side loads, as in a turn. More technically, it is the distance that the resultant force of side-slip occurs behind the geometric center of the contact patch.

Outline of tires

The following outline is provided as an overview of and topical guide to tires:

References

  1. 1 2 3 Foale, Tony (2006). Motorcycle Handling and Chassis Design (Second ed.). Tony Foale Designs. pp. 2–23 to 2–26. ISBN   978-84-933286-3-4.
  2. 1 2 3 4 5 6 Cossalter, Vittore (2006). Motorcycle Dynamics (Second ed.). Lulu.com. pp. 47–48. ISBN   978-1-4303-0861-4.
  3. 1 2 3 4 Wong, Jo Yung (2008). Theory of ground vehicles (Second ed.). Wiley. pp. 40–43. ISBN   978-0-470-17038-0.
  4. ↑ Pacejka, Hans B. (2006). Tyre and vehicle dynamics (2nd ed.). SAE International. p. 162. ISBN   978-0-7680-1702-1. For small angles, the camber thrust is approximated by the product of the camber stiffness and the camber angle.
  5. 1 2 Puhn, Fred (1981). How to Make Your Car Handle. Penguin Putnam. p. 87. ISBN   0-912656-46-8.
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