CDL Practice Tests: Weight & Balance

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Question #662 (1 of 10)

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What is the correct method of determining what percentage of fuel is distributed between the steer axle and the drive axles?

  • Weigh the truck, then immediately fuel up, and then immediately re-weigh the truck to see what percentage of the added weight went to the steer axle, and what percentage went to the drive axles.
  • Weigh the truck after running 100 miles, then immediately fuel up, and then re-weigh the truck to see what percentage of the added weight went to the steer axle, and what percentage went to the drive axles.
  • Weigh the truck, then drive exactly 100 miles, and then re-weigh the truck to see what percentage of the added weight went to the steer axle, and what percentage went to the drive axles.
  • Weigh the truck immediately after fueling, then run exactly 100 miles, and then re-weigh the truck to see what percentage of the added weight came off the steer axles.
In order to accurately determine what percentage of fuel weight goes to your steer axle versus your drive axles you can simply weight the truck, then immediately fuel up, and then immediately re-weigh the truck to see what percentage of the added weight went to the steer axle, and what percentage went to the drive axles.
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Question #638 (2 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?

  • 14,000 pounds
  • None of these are correct
  • 12,000 pounds
  • 20,000 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 #646 (3 of 10)

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What are the two most common tandem slider rail hole spacings, and roughly how much weight is transferred per hole?

  • 6 inches apart - 250 pounds per hole
    10 inches apart - 500 pounds per hole
  • 4 inches apart - 250 pounds per hole
    6 inches apart - 400 pounds per hole
  • 4 inches apart - 450 pounds per hole
    6 inches apart - 200 pounds per hole
  • 6 inches apart - 350 pounds per hole
    8 inches apart - 550 pounds per hole
The two main hole spacings you'll find are 4 inches and 6 inches. You can estimate that you will move 250 pounds per hole for 4 inch spacing, and 400 pounds per hole for 6 inch spacing.
There will be some variance here, but generally speaking these are very good estimates and they work very well. You'll learn to recognize the spacing by glancing at them eventually, but in the beginning you might want to measure quick so you know how far to slide the tandems.
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Question #622 (4 of 10)

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What can be the result of too much weight on the back of the trailer?

  • 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
  • You won't be able to fuel up properly without being overweight
  • The steer tires won't grip properly
  • The steering will feel "heavy" and sluggish
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
Balancing the weight of your truck properly across the axles is a legal requirement because there are so many safety factors involved.
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Question #620 (5 of 10)

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What is the Federal Standard for maximum weight on a tandem axle vehicle?

  • 30,000 pounds
  • 27,000 pounds
  • 34,000 pounds
  • 37,000 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 #661 (6 of 10)

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Where will the weight of fuel be distributed?

  • Mostly to your drive axles, with some going onto the steer axle.
  • Entirely on your steer axle
  • Entirely on your drive axles
  • Mostly to your steer axle, with some going onto the drive axles.
The weight of the fuel in your tanks will be distributed mostly to your steer axle, with some going onto the drive axles.
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Question #642 (7 of 10)

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Which of the following will alter the gross vehicle weight?

  • Sliding the tractor 5th wheel
  • Adding more fuel to the tanks
  • Sliding the trailer tandems
  • Moving the cargo toward the rear of the trailer

The final key point to understand when it comes to weight transfer is that none of the methods of redistributing weight between the different sets of axles, including sliding your 5th wheel, sliding your tandems, or moving the cargo around will have any affect on your gross weight.

The only way to affect the gross vehicle weight would be to add or remove weight from the vehicle. Adding or burning off fuel, or adding or removing cargo would be two examples of ways to alter the gross vehicle weight.

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Question #630 (8 of 10)

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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?

  • 20,000 pounds
  • 12,300 pounds
  • 12,000 pounds
  • 34,000 pounds
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
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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Question #640 (9 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
  • The amount of fuel onboard and the placement of the fuel tanks
  • The position of the trailer's tandems
  • All of these factors affect the weight distribution across the axles

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 #660 (10 of 10)

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What is the best way to determine what percentage of the weight of fuel will go to each set of axles?

  • The percentage is standardized amongst manufacturers and is the same for every truck
  • Ask another driver what their numbers are
  • Weigh the truck immediately before and after fueling, and do a simple calculation
  • Simply go by the number of gallons of fuel each tank holds
The best way to determine what percentage of your fuel will go to each set of axles is to weigh the truck immediately before and after fueling, and do a simple calculation
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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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