CDL Practice Tests: Weight & Balance

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Question #638 (1 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?

  • None of these are correct
  • 12,000 pounds
  • 20,000 pounds
  • 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 #674 (2 of 10)

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Sliding the 5th wheel will change the weight distribution almost exclusively between which sets of axles?

  • The steer axle is the only one affected by fuel
  • The steer axle and the trailer tandems
  • The drive axles and the trailer tandems
  • The steer axle and the drive axles
Sliding the 5th wheel will change the weight distribution almost exclusively between the steer axle and the drive axles.
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Question #672 (3 of 10)

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Using the following numbers for your calculations, how much weight will come off your steer axle?

Miles per gallon: 7
Miles travelled: 280
Percenatage of fuel weight on steer axle: 80%

  • 300 pounds
  • 256 pounds
  • 310 pounds
  • 280 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 7 miles per gallon and you travel 280 miles:

280/7 = 40 gallons of fuel

40 gallons x 8 pounds per gallon = 320 pounds of total fuel burned off

Since 80% of the weight of fuel goes on our steer axle, we need to know what 80% of 320 is:

80 x 320 / 100 = 256 pounds coming off the steer axle
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Question #660 (4 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
  • Ask another driver what their numbers are
  • 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
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 #651 (5 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 6 holes - 33,950 drive axles - 32,350 trailer tandems
  • Slide tandems back 7 holes - 33,750 drive axles - 32,550 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 #631 (6 of 10)

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What are the two primary laws governing the placement of the tandems?

  • The Bridge Formula and the maximum allowed length from Kingpin to trailer tandems.
  • The tire load rating of the drive axle tires and the minimum clearance law
  • The maximum width of 8' 6" on Interstate Highways and the maximum trailer length law
  • The overall gross weight of the vehicle and the maximum percentage of weight on trailer tandems
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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Question #649 (7 of 10)

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You receive a scale ticket and your drive axles are 35,400 and your trailer tandems are 31,100. Based upon the two most common tandem slider rail hole spacings, what is the minimum number of holes you would have to slide the tandems to get the weight legal, and in which direction?

  • 6 inch spacing - slide tandems back 5 holes
    4 inch spacing - slide tandems back 7 holes
  • 6 inch spacing - slide tandems back 4 holes
    4 inch spacing - slide tandems back 6 holes
  • 6 inch spacing - slide tandems forward 5 holes
    4 inch spacing - slide tandems forward 7 holes
  • 6 inch spacing - slide tandems forward 4 holes
    4 inch spacing - slide tandems forward 6 holes
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 35,400 pounds on the drive axles you must move a minimum of 1,400 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 6 inch spacing you're moving 400 pounds per hole so you need to move 4 holes to shift a minimum of 1,400 pounds (400 x 4 = 1,600).

With 4 inch spacing you're moving 250 pounds per hole so you need to move 6 holes to shift a minimum of 1,400 pounds (250 x 6 = 1,500).
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Question #658 (8 of 10)

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If you load cargo into the overhang portion of the trailer, what will be the result?

  • You will put more weight on the trailer tandems than the cargo itself weighs, and you will actually take a little bit of weight off the drive axles at the same time.
  • You will evenly distribute the load across the drive axles and trailer tandems, but the steer axle could now be overweight
  • You will put less weight on the trailer tandems than the cargo itself weighs, and you will actually add a little bit of weight to the drive axles at the same time.
  • The center of gravity will be moved toward the front of the trailer and you will have to slide the trailer tandems all the way to the rear of the 53 foot trailer
Because the trailer pivots up and down at the kingpin above the drive axles, the floor of the trailer acts as a lever pushing down against the trailer tandems when freight is loaded into the overhang portion of the trailer. The further back you load the freight into the overhang portion of the trailer, the more leverage it creates. The net effect of this leverage is that you're putting more weight on the trailer tandems than the cargo itself weighs, and you will actually take a little bit of weight off the drive axles at the same time.
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Question #647 (9 of 10)

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Your trailer has a 6 inch hole spacing in the tandem slider rail and your trailer tandems are 900 pounds overweight. What is the minimum number of holes you will have to slide the tandems to get the tandems within legal limits?

  • 1 hole
  • 3 holes
  • 4 holes
  • 2 holes
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.
6 inch hole spacing means you'll move approximately 400 pounds per hole. In order to move a minimum of 900 pounds, you have to move at least 3 holes (400 x 3 = 1200).
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Question #661 (10 of 10)

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Where will the weight of fuel be distributed?

  • Entirely on your steer axle
  • Entirely on your drive axles
  • Mostly to your steer axle, with some going onto the drive axles.
  • Mostly to your drive axles, with some going onto the steer axle.
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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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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