Rollover Risks
What this domain covers
Rollover questions test whether you understand center of gravity and centrifugal force. A combination vehicle can roll over at speeds that feel safe, especially when the load is high, the trailer is light, or the curve is tighter than it looks.
Core rules
- A high center of gravity reduces stability. Heavy loads placed high, tanker liquids, and tall trailers increase rollover risk.
- Centrifugal force increases with speed and with a tighter curve. The force pushes the vehicle outward; if it exceeds the vehicle’s stability, the trailer or tractor rolls.
- Enter curves and ramps below the posted speed, especially when loaded high or when the surface is wet or icy.
- Do not brake hard in a curve. Brake before the curve, then maintain a steady speed through it.
- Avoid sudden steering. A quick lane change can start a rollover even without a curve.
- The trailer can roll over while the tractor remains upright, so mirror checks and smooth inputs matter.
Worked example
A posted ramp curve is 35 mph. You enter at 45 mph with a high, heavy load. Reasoning: centrifugal force rises sharply with speed, and the high center of gravity reduces the margin before the trailer lifts. The safe response is to slow before the ramp, not to brake midway through the curve. If you are already too fast, hold the wheel steady and reduce speed smoothly rather than jerking the wheel.
Traps that cost marks
- Thinking a lightly loaded trailer is always more stable; an empty or light trailer can bounce and amplify sway.
- Braking hard inside the curve.
- Overcorrecting after the trailer leans.
- Assuming the posted speed is safe for a high-center-of-gravity combination in bad weather.