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3.2.2 – Legal Weight Limits
You must keep weights within legal limits. States have maximums for GVWs, GCWs and axle weights. Often, maximum axle weights are set by a bridge formula. A bridge formula permits less maximum axle weight for axles that are closer together. This is to prevent overloading bridges and roadways.
Problems caused by overloading:
- Overloading can have bad effects on steering, braking and speed control
- Overloaded trucks have to go very slowly on upgrades and may gain too much speed on downgrades.
- Stopping distance increases.
- Brakes can fail when forced to work too hard.
During bad weather or in mountains, it may not be safe to operate at legal maximum weights. Take this into account before driving.
3.2.3 – Do Not Be Top-heavy
The height of the vehicle's center of gravity is important for safe handling. A high center of gravity (cargo piled up high or heavy cargo on top) means you are more likely to tip over. It is most dangerous in curves or if you have to swerve to avoid a hazard. It is important to distribute the cargo so it is as low as possible. Put the heaviest parts of the cargo under the lightest parts.
3.2.4 – Balance the Weight
Poor weight balance can make vehicle handling unsafe.
Too much weight on the steering axle can cause hard steering. It can damage the steering axle and tires.
Under-loaded front axles (caused by shifting weight too far to the rear) can make the steering axle weight too light to steer safely.
Too little weight on the driving axles can cause poor traction. The drive wheels may spin easily.
Cargo that is loaded with a high center of gravity creates a greater chance of rollover. On flatbed vehicles, there is also a greater chance that the load will shift to the side or fall off.
Multiple-Choice Questions:
Which of the following is true about a vehicle with a high center of gravity:
- It's most dangerous in curves or when swerving because it has a better chance of tipping over. You should distribute the cargo so it is as low as possible.
- The weight is loaded too low to the floor of the trailer, making the vehicle unstable. Try to move more weight higher off the ground so the vehicle will lean a little in the turns for better traction.
- It doesn't affect the vehicle much. You may notice it takes a little longer to get stopped, but only about 10% longer.
- You must increase your following distance and make sure you ride the brakes a little while going around a curve.
The height of the vehicle's center of gravity is important for safe handling. A high center of gravity (cargo piled up high or heavy cargo on top) means you are more likely to tip over. It is most dangerous in curves or if you have to swerve to avoid a hazard. It is important to distribute the cargo so it is as low as possible. Put the heaviest parts of the cargo under the lightest parts.
Under-loaded front axles (caused by shifting weight too far to the rear) can:
- Cause the tractor to spin out more easily when you apply the gas on slick roads
- Create a dangerous situation where the weight in the trailer is too far forward
- Make the steering axle weight too light to steer safely
- Make the steering axle weight too heavy to steer safely
Too little weight on the driving axles can:
- Cause the cargo in the trailer to shift forward, creating a dangerous situation
- Create a dangerous situation where the weight in the trailer is too far forward
- Make the front wheels lock up more easily under braking
- Cause poor traction. The drive wheels may spin easily.
What is the bridge formula, and why does it exist?
- A bridge formula permits less maximum axle weight for trailer axles than for tractor drive axles. This is to prevent overloading bridges and roadways.
- A bridge formula permits more weight to be loaded onto the steer tires than would normally be allowed. This is to prevent overloading bridges and roadways.
- A bridge formula permits greater maximum axle weight for axles that are closer together. This is to prevent the tires from overheating due to overloading.
- A bridge formula permits less maximum axle weight for axles that are closer together. This is to prevent overloading bridges and roadways.
Which of the following is true about overloading a truck:
- Stopping distance increases.
- All these are true
- Overloaded trucks have to go very slowly on upgrades and may gain too much speed on downgrades.
- Overloading can have bad effects on steering, braking and speed control
Problems caused by overloading:
- Overloading can have bad effects on steering, braking and speed control
- Overloaded trucks have to go very slowly on upgrades and may gain too much speed on downgrades.
- Stopping distance increases.
- Brakes can fail when forced to work too hard.
Too much weight on the steering axle can:
- Cause hard steering and damage the steering axle and tires.
- Cause poor traction, making the drive wheels spin easily
- Make the steering axle weight too light to steer safely
- Cause the trailer to lose traction and start sliding around on icy roads
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