CDL Practice Tests: Weight & Balance

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Question #669 (1 of 10)

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Based on the following figures, how much fuel can you legally add while remaining legal on the drive axles?

Percentage of fuel weight to drive axles: 30%
Weight Before Fueling: Steer: 11,275, drives: 33,750, gross: 77,220

  • 110 gallons of fuel
  • 88.5 gallons of fuel
  • 104.13 gallons of fuel
  • 112.75 gallons of fuel
Once you know your current axle weights and the percentage of fuel weight that goes on the drive axles, you can use this formula to calculate the amount of fuel you can take on:

We know that 30% of the weight of fuel will go to the drive axles and you have 250 pounds you can add to the weight of the drive axles and remain legal. So plugging these numbers into the formula, you get:

250/30 = 8.33
8.33x100 = 833
833/8 = 104.13 gallons of fuel you can add
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Question #636 (2 of 10)

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What is the maximum legal weight for the drive axles or trailer tandems?

  • 12,000 pounds
  • 20,000 pounds
  • 26,000 pounds
  • 34,000 pounds

The legal weight limits for each set of axles is:

  • Steer axle varies by state
  • 34,000 for the drive axles
  • 34,000 for the trailer tandems
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Question #642 (3 of 10)

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Which of the following will alter the gross vehicle weight?

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

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 #663 (4 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: 11,450, drives: 33,100, gross: 76,700
After fueling:
steer:11,850, drives: 33,300, gross: 77,300

  • 88% went on the steer axle
    12% went on the drive axles
  • 67% went on the steer axle
    33% went on the drive axles
  • 75% went on the steer axle
    25% went on the drive axles
  • 73% went on the steer axle
    27% 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 (400 pounds), divide it by the total fuel weight added (600 pounds), and then multiply that times 100

400/600 = .67

.67 * 100 = 67% fuel weight to the steer tires

100% - 67% = 33% went on the drive axles.
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Question #655 (5 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?

  • About 5-10 feet in front of the trailer tandems
  • A little closer to the front than to the rear
  • 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 #646 (6 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?

  • 4 inches apart - 450 pounds per hole
    6 inches apart - 200 pounds per hole
  • 4 inches apart - 250 pounds per hole
    6 inches apart - 400 pounds per hole
  • 6 inches apart - 350 pounds per hole
    8 inches apart - 550 pounds per hole
  • 6 inches apart - 250 pounds per hole
    10 inches apart - 500 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 #634 (7 of 10)

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What is low-speed offtracking?

  • 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 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 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 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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Question #660 (8 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
  • Weigh the truck immediately before and after fueling, and do a simple calculation
  • Ask another driver what their numbers are
  • 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 #678 (9 of 10)

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You're loaded heavy with 1/2 tank of fuel onboard. Using the following numbers, where should you move the 5th wheel to get it setup properly?

steer axle: 10,800 pounds
drive axles: 34,700 pounds
Weight transfer: 500 pounds per hole

  • Move the 5th wheel forward 2 holes
  • Move the 5th wheel back 2 holes
  • Move the 5th wheel back 1 hole
  • Move the 5th wheel forward 1 hole
The best way to make sure the 5th wheel is set properly is to scale the truck with a minimum of 1/2 tank of fuel and a very heavy load. Under those circumstances, you will want the 5th wheel positioned so that the steer tires are as close to 12,000 pounds as possible without going over, and the trailer tandems as close to 34,000 as possible without going over.
Moving the 5th wheel forward takes weight off the drive axles and puts it onto the steer axle. If we move it forward 2 holes and it transfers 500 pounds per hole, then we wind up moving 1000 pounds from the drive axles to the steer axle:

steer axle: 11,800 pounds
drive axles: 33,700 pounds
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Question #639 (10 of 10)

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You're in Illinois which allows up to 20,000 pounds on the steer axle. You're heading to Indiana which only allows 12,000 on the steer axle. Your steer tires have a load rating of 6,500 pounds each. What is the maximum legal weight your steer axle can be for each of the two states?

  • 13,000 pounds in Illinois
    12,000 pounds in Indiana
  • 20,000 pounds in Illinois
    13,000 pounds in Indiana
  • 20,000 pounds in Illinois
    12,000 pounds in Indiana
  • 13,000 pounds in Illinois
    13,000 pounds in Indiana
Keep in mind though - 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 for each state.

Illinois

Allows 20,000 pounds on the steer axle

Your tire load rating of 6,500 means your maximum legal weight is 13,000 pounds on the steer axle.

The 13,000 pounds is the most restrictive for Illinois

Indiana

Indiana allows 12,000 on the steer axle

Your tire load rating of 6,500 means your maximum legal weight is 13,000 pounds on the steer axle.

The 12,000 pound limit imposed by Indiana on the steer axle is the most restrictive for Indiana

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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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