Vehicle dynamics is the study of

vehicle A vehicle () is a machine designed for self-propulsion, usually to transport people, cargo, or both. The term "vehicle" typically refers to land vehicles such as human-powered land vehicle, human-powered vehicles (e.g. bicycles, tricycles, velo ...

motion, e.g., how a vehicle's forward movement changes in response to driver inputs, propulsion system outputs, ambient conditions, air/surface/water conditions, etc. Vehicle dynamics is a part of

engineering Engineering is the practice of using natural science, mathematics, and the engineering design process to Problem solving#Engineering, solve problems within technology, increase efficiency and productivity, and improve Systems engineering, s ...

primarily based on

classical mechanics Classical mechanics is a Theoretical physics, physical theory describing the motion of objects such as projectiles, parts of Machine (mechanical), machinery, spacecraft, planets, stars, and galaxies. The development of classical mechanics inv ...

. It may be applied for motorized vehicles (such as automobiles), bicycles and motorcycles,

aircraft An aircraft ( aircraft) is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or the Lift (force), dynamic lift of an airfoil, or, i ...

, and

watercraft A watercraft or waterborne vessel is any vehicle designed for travel across or through water bodies, such as a boat, ship, hovercraft, submersible or submarine. Types Historically, watercraft have been divided into two main categories. *Raf ...

Factors affecting vehicle dynamics

The aspects of a vehicle's design which affect the dynamics can be grouped into drivetrain and braking, suspension and steering, distribution of mass, aerodynamics and tires.

Drivetrain and braking

* Automobile layout (i.e. location of engine and driven wheels) *

Powertrain In a motor vehicle, the powertrain comprises the main components that generate engine power, power and deliver that power to the road surface, water, or air. This includes the internal combustion engine, engine, transmission (mechanics), trans ...

* Braking system

Suspension and steering

Some attributes relate to the

geometry Geometry (; ) is a branch of mathematics concerned with properties of space such as the distance, shape, size, and relative position of figures. Geometry is, along with arithmetic, one of the oldest branches of mathematics. A mathematician w ...

of the suspension,

steering Steering is the control of the direction of motion or the components that enable its control. Steering is achieved through various arrangements, among them ailerons for airplanes, rudders for boats, cylic tilting of rotors for helicopters, ...

and

chassis A chassis (, ; plural ''chassis'' from French châssis ) is the load-bearing framework of a manufactured object, which structurally supports the object in its construction and function. An example of a chassis is a vehicle frame, the underpart ...

. These include: * Ackermann steering geometry *

Axle track In Car, automobiles (and other wheeled vehicles which have two wheels on an axle), the axle track is the distance between the hub Flange, flanges on an axle. Wheel track, track width or simply track refers to the distance between the centerline of ...

Camber angle Camber angle is one of the angles made by the wheels of a vehicle; specifically, it is the angle between the vertical axis of a wheel and the vertical axis of the vehicle when viewed from the front or rear. It is used in the creation of steerin ...

* Caster angle * Ride height *

Roll center The roll center of a vehicle is the notional point at which the cornering forces in the suspension are reacted to the vehicle body. There are two definitions of roll center. The most commonly used is the geometric (or kinematic) roll center, whe ...

* Scrub radius * Steering ratio * Toe * Wheel alignment *

Wheelbase In both road and rail vehicles, the wheelbase is the horizontal distance between the centers of the front and rear wheels. For road vehicles with more than two axles (e.g. some trucks), the wheelbase is the distance between the steering (front ...

Distribution of mass

Some attributes or aspects of vehicle dynamics are purely due to

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

and its distribution. These include: *

Center of mass In physics, the center of mass of a distribution of mass in space (sometimes referred to as the barycenter or balance point) is the unique point at any given time where the weight function, weighted relative position (vector), position of the d ...

Moment of inertia The moment of inertia, otherwise known as the mass moment of inertia, angular/rotational mass, second moment of mass, or most accurately, rotational inertia, of a rigid body is defined relatively to a rotational axis. It is the ratio between ...

* Roll moment *

Sprung mass Sprung mass (or sprung weight), in a vehicle with a suspension, such as an automobile, motorcycle, or a tank, is the portion of the vehicle's total mass that is supported by the suspension, including in most applications approximately half of th ...

* Unsprung mass *

Weight distribution Weight distribution is the apportioning of weight within a vehicle, especially cars, airplanes, and trains. Typically, it is written in the form ''x''/''y'', where ''x'' is the percentage of weight in the front, and ''y'' is the percentage in t ...

Aerodynamics

Some attributes or aspects of vehicle dynamics are purely

aerodynamic Aerodynamics () is the study of the motion of atmosphere of Earth, air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dynamics and its subfield of gas dynamics, and is an ...

. These include: *

Automobile drag coefficient The drag coefficient is a common measure in automotive design as it pertains to aerodynamics. Drag is a force that acts parallel to and in the same direction as the airflow. The drag coefficient of an automobile measures the way the automobile ...

Automotive aerodynamics Automotive aerodynamics is the study of the aerodynamics of road vehicles. Its main goals are reducing drag (physics), drag and wind noise, minimizing roadway noise, noise emission, and preventing undesired lift (force), lift forces and other caus ...

* Center of pressure * Downforce * Ground effect in cars

Tires

Some attributes or aspects of vehicle dynamics can be attributed directly to the

tire A tire (North American English) or tyre (Commonwealth English) is a ring-shaped component that surrounds a Rim (wheel), wheel's rim to transfer a vehicle's load from the axle through the wheel to the ground and to provide Traction (engineeri ...

s. These include: * Camber thrust *

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 ...

Contact patch The 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 (i.e. pressurized) tires, where the term is used strictly to describe the portion of the tire' ...

* Cornering force *

Ground pressure Ground pressure is the pressure exerted on the ground by the tires or tracks of a motorized vehicle, and is one measure of its potential mobility, especially over soft ground. It also applies to the feet of a walking person or machine. Pressure ...

* Pacejka's Magic Formula * Pneumatic trail * Radial Force Variation * Relaxation length *

Rolling resistance Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the Motion (physics), motion when a body (such as a ball, tire, or wheel) Rolling, rolls on a surface. It is mainly caused by Plasticity (physics), non- ...

* Self aligning torque * Skid * Slip angle *

Slip (vehicle dynamics) In (automotive) vehicle dynamics, slip describes the relative motion between a tire and the road surface it is moving on. This slip can be generated either by the tire's angular velocity being greater or less than the free-rolling speed (referred ...

* Spinout * Steering ratio * Tire load sensitivity

Vehicle behaviours

Some attributes or aspects of vehicle dynamics are purely dynamic. These include: * Body flex * Body roll * Bump Steer * Bundorf analysis *

Directional stability Directional stability is the tendency of a vehicle or moving body to keep its orientation aligned with its direction of movement. When a car or an airplane gets turned a little relative to its direction of motion, it might correct itself, over-co ...

* Critical speed *

Noise, vibration, and harshness Noise, vibration, and harshness (NVH), also known as noise and vibration (N&V), is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks. While noise and vibration can be readily measured, ...

* Pitch * Ride quality * Roll * Speed wobble * Understeer, oversteer, lift-off oversteer, and fishtailing * Weight transfer and load transfer * Yaw

Analysis and simulation

The dynamic behavior of vehicles can be analysed in several different ways. This can be as straightforward as a simple spring mass system, through a three- degree of freedom (DoF) bicycle model, to a large degree of complexity using a multibody system simulation package such as MSC ADAMS or Modelica. As computers have gotten faster, and software user interfaces have improved, commercial packages such as CarSim have become widely used in industry for rapidly evaluating hundreds of test conditions much faster than real time. Vehicle models are often simulated with advanced controller designs provided as software in the loop (SIL) with controller design software such as

Simulink Simulink is a MATLAB-based graphical programming environment for modeling, simulating and analyzing multidomain dynamical systems. Its primary interface is a graphical block diagramming tool and a customizable set of block libraries. It offe ...

, or with physical hardware in the loop (HIL). Vehicle motions are largely due to the shear forces generated between the tires and road, and therefore the tire model is an essential part of the math model. In current vehicle simulator models, the tire model is the weakest and most difficult part to simulate.Rachel Evans
Quantum leaps
', Automotive Testing Technology International, September 2015, p.43 quote from MTS' Mark Gillian: "''From an OEM perspective, thermal modelling may be overkill but the tire models are still the weak point of any vehicle model''" The tire model must produce realistic shear forces during braking, acceleration, cornering, and combinations, on a range of surface conditions. Many models are in use. Most are semi-empirical, such as the Pacejka Magic Formula model. Racing car games or simulators are also a form of vehicle dynamics simulation. In early versions many simplifications were necessary in order to get real-time performance with reasonable graphics. However, improvements in computer speed have combined with interest in realistic physics, leading to

driving simulator Driving simulators are used for entertainment as well as in training of driver's education courses taught in educational institutions and private businesses. They are also used for research purposes in the area of human factors and medical rese ...

s that are used for vehicle engineering using detailed models such as CarSim. It is important that the models should agree with real world test results, hence many of the following tests are correlated against results from instrumented test vehicles. Techniques include: * Linear range constant radius understeer * Fishhook *

Frequency response In signal processing and electronics, the frequency response of a system is the quantitative measure of the magnitude and Phase (waves), phase of the output as a function of input frequency. The frequency response is widely used in the design and ...

* Lane change *

Moose test The evasive manoeuvre test (; colloquial: moose test or elk test; Swedish: ''Älgtest'', German: ''Elchtest'') is performed to determine how well a certain vehicle evades a suddenly appearing obstacle. This test has been standardized in ISO 388 ...

* Sinusoidal steering * Skidpad * Swept path analysis