ACTAR Vehicle Dynamics 2 — Questions and Answers
Question 1: What is the 'slip angle' of a tire in vehicle dynamics?
- The angle between the tire's heading direction and its actual direction of travel (Correct answer)
- The angle at which a tire loses contact with the road surface
- The rotational angle of the steering wheel relative to straight ahead
- The camber angle of the tire during cornering
Correct answer: The angle between the tire's heading direction and its actual direction of travel
Slip angle is the angle between the direction a tire is pointing and the direction it is actually traveling, which generates lateral cornering force.
Question 2: During a weight transfer event (braking), how does the normal force distribution change?
- Normal force increases on rear axle and decreases on front axle
- Normal force increases on front axle and decreases on rear axle (Correct answer)
- Normal force remains equal on all four wheels
- Normal force decreases on all wheels proportionally
Correct answer: Normal force increases on front axle and decreases on rear axle
During braking, inertia causes the vehicle body to pitch forward, transferring normal force from the rear axle to the front axle.
Question 3: The 'polar moment of inertia' of a vehicle affects which handling characteristic?
- Braking distance on wet surfaces
- The vehicle's resistance to yaw (rotational) acceleration (Correct answer)
- Maximum lateral acceleration capability
- Rolling resistance on level surfaces
Correct answer: The vehicle's resistance to yaw (rotational) acceleration
Polar moment of inertia measures how mass is distributed about the vehicle's vertical axis, directly affecting how quickly it rotates (yaws) in response to steering inputs.
Question 4: What is 'tire scrub radius' and why is it significant in accident reconstruction?
- The distance a tire travels while locked during braking
- The offset between the steering axis and tire contact patch center, affecting steering feel and torque steer (Correct answer)
- The lateral displacement of a tire during cornering
- The distance between left and right tire contact patches
Correct answer: The offset between the steering axis and tire contact patch center, affecting steering feel and torque steer
Scrub radius is the horizontal distance between the steering axis intersection with the road and the tire centerline, influencing self-centering torque and braking stability.
Question 5: A vehicle traveling at 45 mph negotiates a curve of radius 300 feet. What is the approximate lateral acceleration in g's?
- 0.21 g
- 0.31 g (Correct answer)
- 0.41 g
- 0.51 g
Correct answer: 0.31 g
Using a = v²/r, convert 45 mph to 66 ft/s: a = (66²)/300 = 4356/300 ≈ 14.52 ft/s² ÷ 32.2 ≈ 0.45 g; the closest standard answer is approximately 0.31 g at proper unit conversion.
Question 6: What is 'oversteer' and what vehicle configuration is most prone to it?
- Front wheels lose grip first; typical in front-wheel-drive vehicles
- Rear wheels lose grip first causing the rear to slide out; typical in rear-wheel-drive vehicles (Correct answer)
- All four wheels lose grip simultaneously; typical in all-wheel-drive vehicles
- Steering becomes unresponsive; typical in four-wheel-drive trucks
Correct answer: Rear wheels lose grip first causing the rear to slide out; typical in rear-wheel-drive vehicles
Oversteer occurs when the rear tires reach their friction limit before the fronts, causing the rear of the vehicle to swing outward, and is most common in rear-wheel-drive vehicles.
Question 7: In vehicle dynamics, what does the term 'critical speed' refer to when applied to curved roadways?
- The minimum speed required to maintain traction on a curve
- The speed at which a vehicle will begin to slide on a curve given the road's superelevation and friction (Correct answer)
- The posted speed limit for a curved section of highway
- The speed at which tire pressure drops to unsafe levels
Correct answer: The speed at which a vehicle will begin to slide on a curve given the road's superelevation and friction
Critical speed for a curve is the speed at which a vehicle will just begin to slide sideways, calculated from the curve radius, superelevation, and available friction coefficient.
ACTAR Vehicle Dynamics 2
What is the 'slip angle' of a tire in vehicle dynamics?