CDL Practice Tests: Weight & Balance

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Question #664 (1 of 10)

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You weigh the truck immediately before and after fueling. Based on the following, determine what percentage of the weight goes to each set of axles:

Before fueling:
steer: 11,100, drives: 32,600, gross: 71,400
After fueling:
steer:11,850, drives: 32,850, gross: 72,400

  • 65% went on the steer axle
    35% went on the drive axles
  • 67% went on the steer axle
    33% went on the drive axles
  • 80% went on the steer axle
    20% went on the drive axle
  • 75% went on the steer axle
    25% went on the drive axles
To determine the percentage of fuel weight added to the steer axle, take the weight added to the steer axle, divide it by the total fuel weight added (determined by the change in the gross weight), and then multiply that times 100
To determine the percentage of fuel weight added to the steer axle, take the weight added to the steer axle (750 pounds), divide it by the total fuel weight added (1000 pounds), and then multiply that times 100

750/1000 = .75

.75 * 100 = 75% fuel weight to the steer tires

100% - 75% = 25% went on the drive axles.
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Question #644 (2 of 10)

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What affect will sliding the trailer tandems forward have on the weight distribution?

  • You will put more weight on the steer axle and take weight off the tractor's drive axles
  • You will put more weight on the trailer tandems and take weight off the tractor's drive axles
  • You will take weight off the tractor's drive axles and put more weight on the steer axle
  • You will put less weight on the trailer tandems and put more weight on the tractor's drive axles
By sliding the trailer tandems forward, you will put more weight on the trailer tandems and take weight off the tractor's drive axles.
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Question #653 (3 of 10)

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Ideally, where would you like the cargo's center of gravity located?

  • About 10 feet to the rear the center point of the trailer
  • Centered between your drive axles and your trailer tandems.
  • Roughly centered between the steer axle and the trailer tandems
  • Just slightly behind the tractor's drive axles
You'll want to have the cargo loaded into the trailer so that the center of gravity is centered between your drive axles and your trailer tandems.
If the center of gravity of the cargo is too far to the front or rear of the vehicle, it is entirely possible that you will not be able to get your axle weights legal without reloading the cargo itself.
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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 take weight off the drive axles
  • You will decrease 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 increase the weight on the steer axle and increase the weight on 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 #665 (5 of 10)

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You weigh the truck immediately before and after fueling. Based on the following, determine what percentage of the weight goes to each set of axles:

Before fueling:
steer: 10,200, drives: 31,300, gross: 71,700
After fueling:
steer:11,000, drives: 31,500, gross: 72,700

  • 67% went on the steer axle
    33% went on the drive axles
  • 70% went on the steer axle
    30% went on the drive axles
  • 75% went on the steer axle
    25% went on the drive axles
  • 80% went on the steer axle
    20% went on the drive axles
To determine the percentage of fuel weight added to the steer axle, take the weight added to the steer axle, divide it by the total fuel weight added (determined by the change in the gross weight), and then multiply that times 100
To determine the percentage of fuel weight added to the steer axle, take the weight added to the steer axle (800 pounds), divide it by the total fuel weight added (1000 pounds), and then multiply that times 100

800/1000 = .8

.8 * 100 = 80% fuel weight to the steer tires

100% - 80% = 20% went on the drive axles.
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Question #671 (6 of 10)

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Using 6 miles per gallon as your fuel mileage and 8 pounds per gallon for the weight of fuel, how much total fuel weight will you burn off in 600 miles?

  • 600 pounds of fuel
  • 800 pounds of fuel
  • 850 pounds of fuel
  • 480 pounds of fuel
To figure out how many gallons of fuel you'll burn off, simply divide the number of miles travelled by the miles per gallon

Number of miles travelled / miles per gallon = gallons of fuel burned off
600 miles travelled / 6 miles per gallon = 100 gallons of fuel burned off

100 gallons x 8 pounds per gallon = 800 pounds of fuel burned off
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Question #637 (7 of 10)

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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?

  • 12,300 pounds
  • 15,500 pounds
  • 12,000 pounds
  • 20,000 pounds
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.

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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Question #625 (8 of 10)

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

  • Adding or burning off fuel
  • Raising the center of gravity height of the load
  • Sliding your trailer tandems forward or backward
  • 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 #651 (9 of 10)

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You receive a scale ticket and your drive axles are 35,700 and your trailer tandems are 30,600. Based upon a trailer with 4 inch slider rail hole spacings, what is the minimum number of holes you would have to slide the tandems to get the weight legal, and what would the final weights be?

  • Slide tandems forward 6 holes - 33,750 drive axles - 32,550 trailer tandems
  • Slide tandems back 7 holes - 33,750 drive axles - 32,550 trailer tandems
  • Slide tandems back 6 holes - 33,950 drive axles - 32,350 trailer tandems
  • Slide tandems forward 7 holes - 33,950 drive axles - 32,350 trailer tandems
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.
With 35,700 pounds on the drive axles you must move a minimum of 1,700 pounds off the drive axles. To shift weight off the drive axles and onto the trailer tandems, you slide the trailer tandems forward toward the front of the truck.

With 4 inch spacing you're moving 250 pounds per hole so you need to move 7 holes to shift a minimum of 1,700 pounds (250 x 7 = 1,750).

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Question #621 (10 of 10)

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What are the Federal standards for the gross vehicle weight of a 5 axle commercial vehicle?

  • 22,000 pounds
  • 65,000 pounds
  • 60,000 pounds
  • 80,000 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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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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