CDL Practice Tests: Weight & Balance
Choose A Section:
Go!What is the cargo's center of gravity?
- The distance from the front of the trailer to the center point of the cargo.
- The overall length of the cargo after being loaded into the trailer.
- The average height of the cargo above the trailer floor.
- The center point of the cargo's weight.
Based on the following figures, how much fuel can you legally add while remaining legal on the drive axles?
Weight Before Fueling: Steer: 11,275, drives: 33,800, gross: 77,420
- 119.75 gallons of fuel
- 100 gallons of fuel
- 108.8 gallons of fuel
- 122 gallons of fuel
200/25 = 8
8x100 = 800
800/8 = 100 gallons of fuel you can add
Which of the following will alter the gross vehicle weight?
- Moving the cargo toward the rear of the trailer
- Sliding the trailer tandems
- Adding more fuel to the tanks
- 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.
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:
steer: 11,450, drives: 33,100, gross: 76,700
After fueling:
steer:11,850, drives: 33,300, gross: 77,300
- 75% went on the steer axle
25% went on the drive axles - 88% went on the steer axle
12% went on the drive axles - 67% went on the steer axle
33% went on the drive axles - 73% went on the steer axle
27% went on the drive axles
400/600 = .67
.67 * 100 = 67% fuel weight to the steer tires
100% - 67% = 33% went on the drive axles.
Where will the weight of fuel be distributed?
- Entirely on your drive axles
- Mostly to your drive axles, with some going onto the steer axle.
- Mostly to your steer axle, with some going onto the drive axles.
- Entirely on your steer axle
Which of the following has the greatest affect on the gross vehicle weight?
- Moving the cargo toward the front or rear of the trailer
- The position of the tractor's 5th wheel
- The position of the trailer's tandems
- None of these affect the gross vehicle weight at all
If you are able to exert 200 pounds of force against an object but you are only exerting 50 pounds of force to do so, what method are you applying to make this happen?
- Center of gravity
- Leverage
- Momentum
- Centrifugal Force
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?
- 14,000 pounds
- 20,000 pounds
- None of these are correct
- 12,000 pounds
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.
Why did Congress enacted the Bridge Formula in 1975?
- To prevent over-width trucks from becoming a hazard on narrow bridges
- 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 limit the weight-to-length ratio of a vehicle crossing a bridge.
What is the main factor affecting the low-speed offtracking of a tractor trailer?
- The distance from the trailer kingpin to the center of the trailer rear axle
- The ratio of the length of the tractor to the length of the trailer
- The distance from the steer axle to the drive axles
- The length of the trailer, regardless of the position of the trailer tandems
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. Excessive low-speed offtracking may make it necessary for the driver to swing wide into adjacent lanes to execute the turn (that is, to avoid climbing the inside curbs or striking fixed objects like telephone poles).
This performance attribute is affected primarily by the distance from the trailer kingpin to the center of the trailer rear axle, otherwise known as the wheelbase of the semitrailer. To prevent trucks from being too long to maneuvering safely around turns encountered in cities and towns, the maximum length allowed from the kingpin to the trailer tandems is set by the individual states.
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
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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