Rollover Prevention and Weight Distribution
Rollover Prevention and Weight Distribution
This domain tests why combination vehicles roll over and how weight placement affects steering, traction, and axle loading. Expect questions on center of gravity, speed in curves, sliding fifth wheels and tandems, axle limits, and load securement.
Core rules
- A high center of gravity and fast speed in a curve increase lateral force and rollover risk. Load heavy cargo low and centered.
- Never exceed gross, axle, tire, or bridge-formula limits. Too little weight on the steer axle reduces steering control; too little on the drive axles reduces traction.
- A sliding fifth wheel can move weight between the steer and drive axles. Sliding it forward adds weight to the steer axle; sliding it rearward adds weight to the drives.
- Sliding trailer tandems change trailer axle loading and can adjust kingpin load. Secure cargo so it cannot shift sideways or rearward.
Worked example
A tractor-trailer scales with only 9,800 pounds on the steer axle, below its 12,000-pound limit, while the drive axles are near their limit. The driver slides the fifth wheel forward. This transfers some trailer weight to the steer axle and reduces drive-axle load, improving steering feel and staying within axle ratings.
Traps that cost marks
Braking hard in a curve, carrying a top-heavy load at high speed, ignoring tire load ratings, and assuming any load position is safe are common errors. Do not use the fifth wheel or tandems to exceed a tire or axle limit.
Key points
- High center of gravity and curve speed increase rollover risk.
- Load heavy cargo low and centered.
- Check gross, axle, tire, and bridge-formula limits.
- Sliding the fifth wheel forward adds steer-axle weight.
- Secure cargo against sideways and rearward shift.