Vehicle Dynamics, Stability, and Load-Induced Handling
The core idea
Heavy vehicles have high mass, high centre of gravity, and long swept paths. Handling changes with load, speed, and road. Questions test the physics in practical terms.
Concepts to master
- Centre of gravity (CoG): higher CoG increases rollover risk; a shifted CoG changes axle loads and steering.
- Rollover threshold: lateral acceleration at which the vehicle tips; it falls as CoG rises and as speed increases through a curve.
- Understeer/oversteer: a heavy vehicle tends to understeer; a light steer axle worsens steering control.
- Swept path and off-tracking: rear wheels track inside the front wheels; long vehicles need more room at corners.
- Braking dynamics: load transfer to the front axle affects grip; unbalanced braking can cause jackknife.
- Speed and curve radius: rollover risk rises with the square of speed.
Traps in questions
- Assuming a heavier load always means more grip; it can mean less stability.
- Forgetting off-tracking at tight corners.
- Treating rollover as a braking problem rather than a speed/CoG problem.
- Ignoring that a light steer axle reduces steering authority.
Worked rule of thumb
Slow before the curve, not in it. Rollover risk rises with the square of speed, so halving speed cuts the lateral force to a quarter. Brake in a straight line, then steer.
Key points
- Higher centre of gravity increases rollover risk.
- Rollover risk rises with the square of speed.
- Rear wheels off-track inside the front wheels.
- A light steer axle reduces steering authority.
- Brake before curves, not within them.