CDL Practice Tests: Weight & Balance

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Question #673 (1 of 10)

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Using the following numbers for your calculations, how much weight will come off your drive axles?

Miles per gallon: 6
Miles travelled: 360
Percentage of fuel weight on drive axles: 30%

  • 200 pounds
  • 300 pounds
  • 144 pounds
  • 210 pounds
To calculate the percentage of a value, you simply multiply the total value times the percentage you're looking for, and then divide by 100.
If you're getting 6 miles per gallon and you travel 360 miles:

360/6 = 60 gallons of fuel

60 gallons x 8 pounds per gallon = 480 pounds of total fuel burned off

Since 30% of the weight of fuel goes on our drive axles, we need to know what 30% of 480 is:

30 x 480 / 100 = 144 pounds coming off the drive axles
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Question #621 (2 of 10)

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

  • 80,000 pounds
  • 22,000 pounds
  • 60,000 pounds
  • 65,000 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 #627 (3 of 10)

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Sliding your 5th wheel will redistribute the weight mainly between which two sets of axles?

  • Steer axle and trailer tandems
  • Steer axle and drive axles
  • Drive axles and trailer tandems
  • Trailer tandems and rear axles
Sliding your 5th wheel will redistribute the weight mainly between your steer axle and your drive axles
Sliding the 5th wheel will generally have little or no effect on the weight of your trailer tandems
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Question #659 (4 of 10)

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What is the safe number to use in calculations for the weight of fuel?

  • 7.25 pounds per gallon
  • 6 pounds per gallon
  • 10 pounds per gallon
  • 8 pounds per gallon
The precise weight of diesel fuel will vary based on temperature and humidity, but is generally around 7.25-7.5 pounds per gallon. So the safest bet is to use 8 pounds per gallon as the number you'll plug into your calculations, and that's what we're going to use here.
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Question #632 (5 of 10)

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Why did Congress enacted the Bridge Formula in 1975?

  • To regulate the building of bridge structures so they can support the weight of heavy modern trucks
  • To prevent the maximum tire load rating from being exceeded by narrow axle spacing
  • To prevent over-width trucks from becoming a hazard on narrow bridges
  • To limit the weight-to-length ratio of a vehicle crossing a bridge.
Congress enacted the Bridge Formula in 1975 to limit the weight-to-length ratio of a vehicle crossing a bridge.
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Question #660 (6 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?

  • Weigh the truck immediately before and after fueling, and do a simple calculation
  • The percentage is standardized amongst manufacturers and is the same for every truck
  • Simply go by the number of gallons of fuel each tank holds
  • Ask another driver what their numbers are
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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Question #620 (7 of 10)

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

  • 30,000 pounds
  • 34,000 pounds
  • 27,000 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 #650 (8 of 10)

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You receive a scale ticket and your drive axles are 31,700 and your trailer tandems are 35,100. Based upon a trailer with 6 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 back 3 holes - 33,900 tandems - 32,900 drives
  • Slide tandems back 4 holes - 33,300 tandems - 33,100 drives
  • Slide tandems forward 3 holes - 33,900 tandems - 32,900 drives
  • Slide tandems forward 4 holes - 33,300 tandems - 33,100 drives
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 35,100 pounds on the trailer tandems you must move a minimum of 1,100 pounds off the trailer tandems. To shift weight off the trailer tandems and onto the drive axles, you slide the trailer tandems back toward the rear of the truck.

With 6 inch spacing you're moving 400 pounds per hole so you need to move 3 holes to shift a minimum of 1,100 pounds (400 x 3 = 1,200).

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Question #644 (9 of 10)

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

  • You will put less weight on the trailer tandems and put more weight on 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 more weight on the trailer tandems and take weight off the tractor's drive axles
  • You will put more weight on the steer axle and take weight off 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 #670 (10 of 10)

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Using 7 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 210 miles?

  • 210 pounds
  • 240 pounds
  • 180 pounds
  • 270 pounds
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
210 miles travelled / 7 miles per gallon = 30 gallons of fuel burned off

30 gallons x 8 pounds per gallon = 240 pounds of fuel burned off
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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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