Weight Distribution Practice Questions
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Adding or burning off fuel will mainly change the amount of weight on which axles?
- Steer axle and somewhat on your drive axles
- Drive axles only
- Drive axles and somewhat on your trailer tandems
- Trailer tandems only
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From The CDL Manual
Adding or burning off fuel will mainly change the amount of weight on your steer axle and somewhat on your drive axles
TruckingTruth's Advice:
Most of the weight of the fuel will go on your steer axle. The percentage of weight distributed between your steer and drive axles with regard to fuel will depend on the placement of your fuel tanks.
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What is the main factor that will limit how far back you can slide your tandems?
- The load rating of your drive tires
- The distance between your steer axle and drive axles or "tractor length rating"
- The maximum legal length allowed between your trailer kingpin and your trailer tandems
- The overall height to length ratio of the cargo in the trailer
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From The CDL Manual
The maximum legal length allowed between your trailer kingpin and your trailer tandems will limit how far back you can slide your tandems
TruckingTruth's Advice:
Different states have different laws regarding the maximum length allowed from your kingpin to your trailer tandems and you can look up these values in the Rand McNally Motor Carrier's Atlas
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You have steer tires rated at 6,150 pounds each, and you're in the state of West Virginia which says the legal limit for the steer axle is 20,000 pounds. What's the maximum legal weight you can carry on your steer axle in West Virginia?
- 34,000 pounds
- 12,000 pounds
- 12,300 pounds
- 20,000 pounds
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From The CDL Manual
When distributing weight across a set of axles, you will ultimately be limited by the most restrictive law for any given situation. For instance, if the law states that you can carry 20,000 pounds on your steer axle, but your steer tires have a load rating of 6000 pounds each, then you can only carry a total of 12,000 pounds on your steer axle
TruckingTruth's Advice:
Your steer tires are rated at 6,150 pounds and you have two of them on your steer axle. Therefore you can carry a total of 12,300 pounds (6,150 x 2) on your steer axle. Because you can not legally exceed the load rating of your tires, the fact that West Virginia allows 20,000 pounds on the steer axle doesn't matter. You're ultimately limited by the most restrictive law, which in this case is related to exceeding the steer tire load rating.
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What are the two primary laws governing the placement of the tandems?
- The tire load rating of the drive axle tires and the minimum clearance law
- The Bridge Formula and the maximum allowed length from Kingpin to trailer tandems.
- The overall gross weight of the vehicle and the maximum percentage of weight on trailer tandems
- The maximum width of 8' 6" on Interstate Highways and the maximum trailer length law
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From The CDL Manual
The two primary laws governing the placement of the tandems are the Bridge Formula and the maximum allowed length from Kingpin to trailer tandems.
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Why did Congress enacted the Bridge Formula in 1975?
- To limit the weight-to-length ratio of a vehicle crossing a bridge.
- To prevent over-width trucks from becoming a hazard on narrow bridges
- To prevent the maximum tire load rating from being exceeded by narrow axle spacing
- To regulate the building of bridge structures so they can support the weight of heavy modern trucks
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From The CDL Manual
Congress enacted the Bridge Formula in 1975 to limit the weight-to-length ratio of a vehicle crossing a bridge.
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What is the primary goal of implementing the Bridge Formula?
- To increase the minimum strength of bridges, allowing for heavier gross vehicle weights which improves efficiency
- To prevent overloading the trailer tandems and exceeding the load rating of the trailer tires
- To prevent putting too much weight on a relatively small area, causing damage to road surface and bridge structure.
- To prevent over-length trucks from becoming a hazard on narrow bridges and tight roadways
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From The CDL Manual
The idea (of implementing the bridge formula) was to prevent putting too much weight on a relatively small area, causing damage to road surface and bridge structure.
TruckingTruth's Advice:
A bridge is designed to handle a certain number of pounds per square inch on the surface. By creating the Bridge Formula, Congress made sure that too much weight wasn't concentrated on a small area of a bridge, causing damage to the bridge structure.
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What is low-speed offtracking?
- When taking off from a dead stop, the initial torque of the engine on the drivetrain will cause a slight offtracking of the tractor which could be a hazard to other traffic
- When making a high speed turn, the momentum carried by the trailer will cause it to swing wide and possibly outside the lane of travel
- When a trailer's tandem axles are slightly out of alignment, the rear of the trailer will track off to one side or another instead of directly behind the tractor
- When a combination vehicle makes a low-speed turn the wheels of the rearmost trailer axle follow a path several feet inside the path of the tractor steering axle.
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From The CDL Manual
When a combination vehicle makes a low-speed turn - for example a 90-degree turn at an intersection - the wheels of the rearmost trailer axle follow a path several feet inside the path of the tractor steering axle. This is called low-speed offtracking.
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What is the main factor affecting the low-speed offtracking of a tractor trailer?
- The distance from the steer axle to the drive axles
- The distance from the trailer kingpin to the center of the trailer rear axle
- The ratio of the length of the tractor to the length of the trailer
- The length of the trailer, regardless of the position of the trailer tandems
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From The CDL Manual
When a combination vehicle makes a low-speed turn - for example a 90-degree turn at an intersection - the wheels of the rearmost trailer axle follow a path several feet inside the path of the tractor steering axle. This is called low-speed offtracking. Excessive low-speed offtracking may make it necessary for the driver to swing wide into adjacent lanes to execute the turn (that is, to avoid climbing the inside curbs or striking fixed objects like telephone poles).
This performance attribute is affected primarily by the distance from the trailer kingpin to the center of the trailer rear axle, otherwise known as the wheelbase of the semitrailer. To prevent trucks from being too long to maneuvering safely around turns encountered in cities and towns, the maximum length allowed from the kingpin to the trailer tandems is set by the individual states.
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What is the maximum legal weight for the drive axles or trailer tandems?
- 12,000 pounds
- 34,000 pounds
- 20,000 pounds
- 26,000 pounds
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From The CDL Manual
The legal weight limits for each set of axles is:
- Steer axle varies by state
- 34,000 for the drive axles
- 34,000 for the trailer tandems
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In Oregon, the maximum weight on the steer axle is listed as 600 pounds per inch of tire tread width up to 20,000 pounds. Your steer tires have a load rating of 6,150 pounds each and are 10 inches wide. What is the maximum legal weight your steer axle can carry in Oregon?
- 20,000 pounds
- 12,000 pounds
- 15,500 pounds
- 12,300 pounds
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From The CDL Manual
Kentucky has a limit of 700 pounds per inch of tread width. So if you have a 10 inch wide tire tread, you are allowed a maximum of 7,000 pounds per tire (700 pounds per inch x 10 inches wide) or 14,000 pounds total for the steer axle.
TruckingTruth's Advice:
You must find the most restrictive law to determine your maximum legal weight.
The maximum Oregon allows is 20,000 pounds on the steer axle
The load rating on your tires is 6,150, which would put your maximum legal weight at 12,300 pounds regardless of the fact that there are less restrictive laws.
The maximum Oregon allows by weight is 600 pounds per inch. You have 10 inch tires so that would be a maximum of 6000 pounds per tire, or 12,000 pounds on the steer axle, which is the most restrictive of the various laws. Therefore, 12,000 pounds is your legal limit in this truck in Oregon.
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