CDL Practice Tests: Weight & Balance

Choose A Section:

Go!
Question #636 (1 of 10)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

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

  • 34,000 pounds
  • 12,000 pounds
  • 20,000 pounds
  • 26,000 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
Previous Next
Question #629 (2 of 10)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

What is the main factor that will limit how far back you can slide your tandems?

  • The distance between your steer axle and drive axles or "tractor length rating"
  • The load rating of your drive tires
  • The maximum legal length allowed between your trailer kingpin and your trailer tandems
  • The overall height to length ratio of the cargo in the trailer
The maximum legal length allowed between your trailer kingpin and your trailer tandems will limit how far back you can slide your tandems
Different states have different laws regarding the maximum length allowed from your kingpin to your trailer tandems and you can look up these values in the Rand McNally Motor Carrier's Atlas
Previous Next
Question #621 (3 of 10)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

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

  • 65,000 pounds
  • 80,000 pounds
  • 60,000 pounds
  • 22,000 pounds
  • 20,000 pounds single axle weight
  • 34,000 pounds tandem axle weight
  • 80,000 pounds gross vehicle weight
  • Bridge Formula Calculations
Previous Next
Question #651 (4 of 10)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

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 7 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 6 holes - 33,750 drive axles - 32,550 trailer tandems
  • Slide tandems back 6 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).

Previous Next
Question #676 (5 of 10)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

Using the following numbers, what would be the final result if you moved the 5th wheel forward two holes?

steer axle: 10,800 pounds
drive axles: 34,100 pounds
Weight transfer: 500 pounds per hole

  • steer axle: 11,300 pounds
    drive axles: 33,600 pounds
  • steer axle: 9,800 pounds
    drive axles: 35,100 pounds
  • steer axle: 11,800 pounds
    drive axles: 33,100 pounds
  • steer axle: 10,300 pounds
    drive axles: 34,600 pounds
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.
If you move it forward 2 holes, then:

2 holes x 500 pounds per hole = 1000 pounds of weight transfer from the drive axles to the steer axle.

10,800 + 1000 = 11,800 pounds on the steer axle after transfer

34,100 - 1000 = 33,100 pounds on the drive axles after transfer
Previous Next
Question #671 (6 of 10)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

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?

  • 480 pounds of fuel
  • 850 pounds of fuel
  • 800 pounds of fuel
  • 600 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
Previous Next
Question #659 (7 of 10)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

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

  • 6 pounds per gallon
  • 10 pounds per gallon
  • 7.25 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.
Previous Next
Question #677 (8 of 10)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

Using the following numbers, what would be the final result if you moved the 5th wheel back one hole?

steer axle: 12,300 pounds
drive axles: 33,100 pounds
Weight transfer: 500 pounds per hole

  • steer axle: 11,800 pounds
    drive axles: 33,600 pounds
  • steer axle: 11,300 pounds
    drive axles: 34,100 pounds
  • steer axle: 12,800 pounds
    drive axles: 32,600 pounds
  • steer axle: 12,050 pounds
    drive axles: 33,350 pounds
If you move the 5th wheel toward the rear of the tractor, you will increase the weight on the drive axles and decrease the weight on the steer axle.
If you move it back 1 hole, then:

1 holes x 500 pounds per hole = 500 pounds of weight transfer from the steer axle to the drive axles.

12,300 - 500 = 11,800 pounds on the steer axle after transfer

33,100 + 500 = 33,600 pounds on the drive axles after transfer
Previous Next
Question #655 (9 of 10)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

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?

  • Directly centered above the trailer tandems
  • About 15 feet behind the tractor drive axles
  • About 5-10 feet in front of the trailer tandems
  • A little closer to the front than to the rear
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.
Previous Next
Question #634 (10 of 10)

Give a brief explanation of the problem:

Optional: Leave your email address if you would like a reply:

Report Cancel

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 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 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 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.
Previous Next
Complete!

Choose your next section:

Go!

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.

Why Join Trucking Truth?

We have an awesome set of tools that will help you understand the trucking industry and prepare for a great start to your trucking career. Not only that, but everything we offer here at TruckingTruth is 100% free - no strings attached! Sign up now and get instant access to our member's section:
High Road Training Program Logo
  • The High Road Training Program
  • The High Road Article Series
  • The Friendliest Trucker's Forum Ever!
  • Email Updates When New Articles Are Posted

Apply For Paid CDL Training Through TruckingTruth

Did you know you can fill out one quick form here on TruckingTruth and apply to several companies at once for paid CDL training? Seriously! The application only takes one minute. You will speak with recruiters today. There is no obligation whatsoever. Learn more and apply here:

Apply For Paid CDL Training