CDL Practice Tests: Weight & Balance

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Question #619 (1 of 10)

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What is the Federal standard for the weight limit on a single axle?

  • 15,000 pounds
  • 22,000 pounds
  • 20,000 pounds
  • 12,000 pounds
  • 20,000 pounds single axle weight
  • 34,000 pounds tandem axle weight
  • 80,000 pounds gross vehicle weight
  • Bridge Formula Calculations
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Question #652 (2 of 10)

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What is the cargo's center of gravity?

  • The center point of the cargo's weight.
  • The average height of the cargo above the trailer floor.
  • The overall length of the cargo after being loaded into the trailer.
  • The distance from the front of the trailer to the center point of the cargo.
The center of gravity location of the cargo is the center point of the cargo's weight. In other words, if all of the cargo in your trailer was one solid block, the center of gravity would be the point that the entire block would balance upon like a teeter totter.
Sometimes you will load 22 pallets that all weigh the same. That makes it simple to determine the center of gravity. But often times you'll have a mixed product and you'll have to look over what's being put on the truck so you can get the weight of the cargo roughly centered between the drive axles and trailer tandems.
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Question #645 (3 of 10)

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What factor has the greatest affect on how much weight is moved per hole in the tandem slider rail?

  • The distance between the locking pin holes
  • The amount of fuel you have onboard
  • The center of gravity of the cargo
  • The distance from the drive axles to the trailer tandems
The distance between the locking pin holes on the trailer will be the main factor affecting how much weight is moved per hole. This distance varies between the different trailer manufacturers, and the larger the distance between the holes, the more weight will be shifted with each hole.
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Question #675 (4 of 10)

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If you slide the 5th wheel toward the nose of the tractor, what will be the effect?

  • You will increase the weight on the steer axle and increase the weight on the drive axles
  • You will increase the weight on the steer axle and take weight off the drive axles
  • You will decrease the weight on the steer axle and it will have no effect on the drive axles
  • You will decrease the weight on the steer axle and take weight off the drive axles
If you slide the 5th wheel toward the nose of the tractor you will increase the weight on the steer axle and take weight off the drive axles.
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Question #643 (5 of 10)

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Sliding your trailer tandems toward the front or back of the vehicle will primarily change the weight distribution between which sets of axles?

  • The tractor's drive axles and the steer axle
  • It only removes weight from the trailer tandems
  • The tractor's drive axles and the trailer tandems.
  • The steer axle and the trailer tandems
Sliding your trailer tandems toward the front or back of the vehicle will primarily change the weight distribution between the tractor's drive axles and the trailer tandems.
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Question #640 (6 of 10)

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Which of the following are not a primary factor affecting weight distribution across the axles?

  • The position of the tractor's 5th wheel
  • All of these factors affect the weight distribution across the axles
  • The amount of fuel onboard and the placement of the fuel tanks
  • The position of the trailer's tandems

The primary factors which will affect the weight distribution across a truck's axles are:

  • The position of the trailer's tandems
  • The position of the tractor's 5th wheel
  • The overall weight of the cargo in the trailer and the horizontal (front-to-back) position of its center of gravity
  • The amount of fuel onboard and the placement of the fuel tanks
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Question #655 (7 of 10)

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If unsure of the exact location of the center of gravity of your cargo, where would you rather have the center of gravity located if you couldn't get it centered?

  • A little closer to the front than to the rear
  • About 5-10 feet in front of the trailer tandems
  • Directly centered above the trailer tandems
  • About 15 feet behind the tractor drive axles
If unsure of the exact location of the center of gravity of your cargo, you'd rather have the load a little closer to the front than to the rear. You can slide the trailer tandems forward as far as you would like to compensate for too much weight on the nose of the trailer, but the kingpin to trailer tandem length limitations will prevent you from going too far back with your trailer tandems.
A lot of times you'll be loading mixed cargo which will make it quite difficult to determine the exact center of gravity of the load. So when you're making your best guess, try to make sure it's a little forward of the center point between the drive axles and trailer tandems. That will give you the best chance of being able to adjust the trailer tandems so that the load will be legal.
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Question #625 (8 of 10)

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Which of the following techniques will not change the weight distribution across your axles?

  • Raising the center of gravity height of the load
  • Sliding your trailer tandems forward or backward
  • Adding or burning off fuel
  • Changing the weight distribution of the cargo along the length of the trailer

There are several ways to distribute or redistributing the overall weight of the vehicle across the different sets of axles. You will affect weight distribution by:

  • Changing the weight distribution of the cargo along the length of the trailer, or moving the cargo around after the truck has been loaded. This will distribute the weight mainly between your drive axles and trailer tandems
  • Sliding your trailer tandems forward or backward will redistribute the weight mainly between your drive axles and trailer tandems
  • Sliding your 5th wheel will redistribute the weight mainly between your steer axle and your drive axles
  • Adding or burning off fuel will mainly change the amount of weight on your steer axle and somewhat on your drive axles also, depending upon the placement of your fuel tanks.
If you move the center of gravity either toward the front or rear of the trailer, it will change the weight distribution across the axles. But raising or lowering the center of gravity of the load will not change its weight distribution across the axles.
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Question #638 (9 of 10)

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California allows 20,000 pounds maximum on the steer axle. The tread width of your tires is 11 inches, and the load rating on your steer tires is 7000 pounds. How much weight can you carry on your steer axle in California?

  • 12,000 pounds
  • 20,000 pounds
  • None of these are correct
  • 14,000 pounds
Even if they allow 14,000 pounds on the steer axle, you have to have tires that are rated to carry that much weight. If your steer tires have a tire load limit of 6,000 pounds each, you can only carry 12,000 pounds on your steer axle, regardless of state laws.

We have to find the most restrictive law to determine our maximum weight.

California allows up to 20,000 pounds on the steer axle

There is no requirement based upon tread width in California, so the width of your steer tires is irrelevant for this example

Your steer tires have a maximum load rating of 7,000 pounds each, which would therefore limit your legal steer axle weight to 14,000 pounds. This is the most restrictive of the laws, so 14,000 pounds is your legal weight limit in this case.

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Question #634 (10 of 10)

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What is low-speed offtracking?

  • 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 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 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.
  • 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 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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About The Weight And Balance Section

This section was created by Trucking Truth to help people understand how to load cargo, scale the truck, and understand the laws about truck weight limits. These materials will not be on your written CDL exams but it is critical that every truck driver knows these materials.

Types Of Weight Limits

There are four basic weight limits: single axle, tandem axle, bridge formula, and gross vehicle. The Federal Standards are as follows:

  • 20,000 pounds single axle weight
  • 34,000 pounds tandem axle weight
  • 80,000 pounds gross vehicle weight
  • Bridge Formula Calculations

Why Do These Different Weight Limits Exist?

There are a long list of critical safety issues which require putting limitations on the gross weight, axle weights, the weight distribution across the length of a vehicle, and the weight distribution across a minimum number of axles.

  • Putting too much weight on a small area of the road surface can cause ruts, cracks, and potholes
  • Putting too much weight on a small area of a bridge surface can cause structural damage to the bridge
  • Too much weight on your steer axle can lead to a "heavy steering" feel and may cause the truck to react improperly to steering inputs
  • Not enough weight on your steer axle can lead to a loss of traction for your steer tires
  • Improper weight balance between your tractor drive tires and trailer tandems can lead to poor traction and an increased risk of jackknifing
  • Too much weight toward the back of the trailer can lead to a "pendulum effect", causing the rear of the trailer to sway back and forth while driving down the highway or jackknife going around a curve
  • Overloading a tire beyond it's maximum tire load capacity can cause tire damage and blowouts
  • Overloading the suspension system of the truck can cause damage to the suspension system which could easily lead to loss of control of the vehicle

So as you can see, it's critical in so many ways to make sure that we follow the weight limits in strict accordance with the law. It is incredibly dangerous to overload a vehicle or to have the weight improperly distributed across the axles.

Methods Of Weight Transfer

There are several ways to distribute the overall weight of the vehicle across the different sets of axles. You will affect weight distribution by:

  • Changing the weight distribution of the cargo along the length of the trailer, or moving the cargo around after loading the truth. This will distribute the weight mainly between your drive axles and trailer tandems
  • Sliding your trailer tandems forward or backward will redistribute the weight mainly between your drive axles and trailer tandems
  • Sliding your 5th wheel will redistribute the weight mainly between your steer axle and your drive axles
  • Adding or burning off fuel will mainly change the amount of weight on your steer axle and somewhat on your drive axles also, depending upon the placement of your fuel tanks.

Limitations On Weight Transfer

There are several factors that will reduce the amount of weight we can transfer between the different sets of axles on the truck:

  • Federal laws limit the maximum weight on any set of axles and the gross vehicle weight - 20,000 pounds single axle, 34,000 pound tandem axles, 80,000 pounds GVW
  • The bridge law formula limits the maximum amount of weight you can carry across any set of axles based upon the number of axles and the spacing between them (we'll discuss this formula soon).
  • The maximum legal length allowed between your trailer kingpin and your trailer tandems will limit how far back you can slide your tandems
  • The load rating of the tires you have will determine the maximum amount of weight allowed on any particular tire
  • The load rating of the suspension system will limit the amount of weight you can have on any axle

The Bridge Formula

bridge law formula and regulations for trucks

Congress enacted the Bridge Formula in 1975 to limit the weight-to-length ratio of a vehicle crossing a bridge. They accomplished this either by spreading weight over additional axles or by increasing the distance between axles.

The idea here was to prevent putting too much weight on a relatively small area, causing damage to the road surface and bridge structure. By requiring trucks to spread the weight across a longer distance and distributing the weight across more axles, you help prevent damage to the bridges and roadways.

Compliance with Bridge Formula weight limits is determined by using the following formula:

W = the overall gross weight on any group of two or more consecutive axles to the nearest 500 pounds.

L = the distance in feet between the outer axles of any group of two or more consecutive axles.

N = the number of axles in the group under consideration.

Altering The Weight Distribution

The primary factors which will affect the weight distribution across a truck's axles are:

  • The position of the trailer's tandems
  • The position of the tractor's 5th wheel
  • The overall weight of the cargo in the trailer and the horizontal (front-to-back) position of its center of gravity
  • The amount of fuel onboard and the placement of the fuel tanks

In the coming pages, we'll go through these one at a time and learn to apply each one individually. Later we'll put them all together and show you how to get your truck's weight distribution legal out on the highways, coast to coast, under any circumstances.

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