Vehicle dynamics

Vehicle dynamics refers to the dynamics of vehicles, here assumed to be ground vehicles. Vehicle dynamics is a part of engineering primarily based on classical mechanics but it may also involve chemistry, solid state physics, electrical engineering, communications, psychology, control theory, etc.

This article applies primarily to automobiles. For single-track vehicles, specifically the two-wheeled variety, see Bicycle and motorcycle dynamics. For aircraft see Aerodynamics. For watercraft see Hydrodynamics.

Components

Components, attributes or aspects of vehicle dynamics include:

• Electronic Stability Control (ESC)
• Steering
• Suspension
• Traction control system (TCS)

Aerodynamic specific

Some attributes or aspects of vehicle dynamics are purely aerodynamic. These include:

• Automobile drag coefficient
• Automotive aerodynamics
• Center of pressure
• Downforce
• Ground effect in cars

Geometry specific

Some attributes or aspects of vehicle dynamics are purely geometric. These include:

• Ackermann steering geometry
• Axle track
• Camber angle
• Caster angle
• Ride height
• Toe
• Wheelbase

Mass specific

Some attributes or aspects of vehicle dynamics are purely due to mass and its distribution. These include:

• Center of mass
• Moment of inertia
• Roll center
• Sprung mass
• Unsprung mass
• Weight distribution

Motion specific

Template:Main Some attributes or aspects of vehicle dynamics are purely dynamic. These include:

• Body flex
• Bump Steer
• Critical speed
• Load transfer
• Noise, vibration, and harshness
• Oversteer
• Ride quality
• Speed wobble
• Understeer
• Weight transfer

Tire specific

Some attributes or aspects of vehicle dynamics can be attributed directly to the tires. These include:

• Camber thrust
• Circle of forces
• Contact patch
• Cornering force
• Ground pressure
• Pacejka's Magic Formula
• Pneumatic trail
• Rolling resistance
• Self aligning torque
• Slip angle
• Slip (vehicle dynamics)
• Steering ratio
• Tire load sensitivity

Driving techniques

Driving techniques which relate to, or improve the stability of vehicle dynamics include:

• Cadence braking
• Threshold braking
• Double declutching
• Drifting (motorsport)
• Handbrake turn
• Heel-and-Toe
• Left-foot braking
• Opposite lock
• Scandinavian flick

Analysis and simulation

The dynamic behavior of vehicles can be analysed in several different ways. This can be a straightforward as a simple spring mass system, through a 3 degree of freedom (DoF) bicycle model, which can be solved by hand by a keen mathematician, or can be simulated in any degree of complexity on a computer, using MBS packages such as Modelica, MSC ADAMS, or any of several others. Typically these will have between twenty and several hundred DoFs, although the upper limit is increasing. The tire and driver models are usually the biggest headaches in this process. The tire is typically modelled by a Pacejka Magic Formula model, or a similar concept. Racing car games or simulators are also a form of vehicle dynamics simulation, although many simplifications are necessary in order to get real time performance with reasonable graphics.

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
• Lane change
• Moose test
• Sinusoidal steering
• Swept path analysis