ACTAR Vehicle Dynamics 4

Question 1

What is 'yaw rate' and how is it used in accident reconstruction?

Accepted Answer

The rate at which a vehicle rotates about its vertical axis, measured in degrees per second

Answer

Yaw rate is the angular velocity of the vehicle about its vertical (z) axis; modern EDR systems record it and reconstructionists use it to determine vehicle rotation during pre-crash maneuvers.

Question 2

What is the relationship between tire cornering stiffness and slip angle?

Accepted Answer

Cornering stiffness is the lateral force generated per degree of slip angle; higher stiffness means more force per degree

Answer

Cornering stiffness (Cα) is the ratio of lateral force to slip angle in the linear region of the tire's force curve, indicating how effectively a tire converts slip angle into cornering force.

Question 3

During an evasive maneuver, a vehicle understeers severely and runs off the road. Which tire condition most commonly causes this in a front-wheel-drive vehicle?

Accepted Answer

Front tires underinflated or overloaded causing front axle saturation before rear axle

Answer

In front-wheel-drive vehicles, underinflated or overloaded front tires reach friction saturation earlier, preventing steering response and causing the vehicle to push straight off the intended path.

Question 4

The 'magic formula' tire model developed by Pacejka is used to predict what?

Accepted Answer

Tire force and moment characteristics as functions of slip angle, slip ratio, camber, and normal load

Answer

Pacejka's Magic Formula is an empirical mathematical model that accurately describes the complex nonlinear relationships between tire forces/moments and operating conditions including slip angle, slip ratio, and vertical load.

Question 5

What is the effect of 'aerodynamic lift' on vehicle handling at high speeds, relevant to reconstruction of high-speed crashes?

Accepted Answer

Aerodynamic lift reduces tire normal force, decreasing available friction and cornering capability

Answer

Aerodynamic lift reduces the effective weight pressing the tires against the road, lowering normal force and therefore reducing the maximum friction force available for braking and cornering.

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

ACTAR Vehicle Dynamics 4