ACTAR Vehicle Dynamics 5

Question 1

What is 'friction circle' (or friction ellipse) concept and how does it apply to vehicle dynamics?

Accepted Answer

The limit of combined longitudinal and lateral tire forces; the vector sum cannot exceed maximum available friction

Answer

The friction circle represents the maximum combined force a tire can generate; if longitudinal (braking/acceleration) forces are high, less lateral force is available for cornering, and vice versa.

Question 2

What is the purpose of 'anti-lock braking system' (ABS) from a vehicle dynamics perspective in accident reconstruction?

Accepted Answer

ABS modulates brake pressure to prevent wheel lockup, preserving steering control while optimizing braking force near peak friction

Answer

ABS rapidly modulates brake pressure to keep wheels near peak slip ratio (typically 10-20%), maintaining tire cornering capability and directional control while achieving near-peak longitudinal deceleration.

Question 3

In reconstruction of a tripped rollover, what is the primary triggering mechanism?

Accepted Answer

An external force or surface feature (curb, soft shoulder, guardrail) that arrests lateral tire motion while inertia continues to rotate the body

Answer

A tripped rollover occurs when a wheel is caught by an external object or soft soil that stops lateral wheel movement while the vehicle's inertia causes the body to continue rotating over the tripped wheel.

Question 4

What is 'tire relaxation length' and why does it matter in high-speed maneuver analysis?

Accepted Answer

The distance a tire must travel before lateral forces build to their steady-state value after a slip angle change

Answer

Tire relaxation length is the travel distance required for lateral force to reach approximately 63% of its steady-state value after a step change in slip angle, causing a time delay in vehicle response to steering inputs.

Question 5

How does differential action affect vehicle yaw behavior during cornering?

Accepted Answer

A locked differential promotes understeer by forcing both driven wheels to the same speed

Answer

A locked or limited-slip differential forces the outside wheel (which needs to travel farther in a turn) to spin at the same rate as the inside wheel, creating scrub and understeer forces that resist turning.

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

ACTAR Vehicle Dynamics 5