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

- 27,000 pounds
- 34,000 pounds
- 30,000 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

Where will the weight of fuel be distributed?

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

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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What are the two most common tandem slider rail hole spacings, and roughly how much weight is transferred per hole?

- 6 inches apart - 250 pounds per hole

10 inches apart - 500 pounds 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

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

- The steer axle and the drive axles
- The steer axle is the only one affected by fuel
- The drive axles and the trailer tandems
- The steer axle and the trailer tandems

Sliding the 5th wheel will change the weight distribution almost exclusively between the steer axle and the drive axles.

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

- You will evenly distribute the load across the drive axles and trailer tandems, but the steer axle could now be overweight
- 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.
- 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
- 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.

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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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: 12,300 pounds

drive axles: 33,100 pounds

Weight transfer: 500 pounds per hole

drive axles: 33,100 pounds

Weight transfer: 500 pounds per hole

- Move the 5th wheel back 1 hole
- Move the 5th wheel forward 2 holes
- Move the 5th wheel back 2 holes
- 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.

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 we move it back 1 hole and it transfers 500 pounds per hole, then we wind up moving 500 pounds from the steer axle to the drive axles:

steer axle: 11,800 pounds

drive axles: 33,600 pounds

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steer axle: 11,800 pounds

drive axles: 33,600 pounds

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

Load rating of steer tires: 6,150 pounds

Percentage of fuel weight to steer axle: 80%

Steer axle weight limit in states you're travelling: 20,000 pounds

Weight Before Fueling: Steer: 11,450, drives: 33,100, gross: 76,700

Percentage of fuel weight to steer axle: 80%

Steer axle weight limit in states you're travelling: 20,000 pounds

Weight Before Fueling: Steer: 11,450, drives: 33,100, gross: 76,700

- 121.25 gallons
- 132.81 gallons
- 119.5 gallons
- 146 gallons

Once you know your current axle weights and the percentage of fuel weight that goes on the steer axle, you can use this formula you can calculate the amount of fuel you can take on:

Because your steer tires are rated at 6,150 and the legal weight limit is 20,000 pounds for the steer axle in the states you're travelling in, the most restrictive law would be to not exceed the tire load rating. In this case, you can have 12,300 on your steer axle. Right now you have 11,450 on your steer axle, which means you can add 850 pounds to your steer axle and still be legal.

Because we know that 80% of the weight of fuel will go to the steer axle and you can add 850 pounds to your steer axle, we can plug the numbers into the formula above.

850/80 = 10.62

10.62 x 100 = 1062

1062/8 = 132.75 gallons of fuel you can add

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Because we know that 80% of the weight of fuel will go to the steer axle and you can add 850 pounds to your steer axle, we can plug the numbers into the formula above.

850/80 = 10.62

10.62 x 100 = 1062

1062/8 = 132.75 gallons of fuel you can add

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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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?

- 800 pounds of fuel
- 480 pounds of fuel
- 850 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

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

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100 gallons x 8 pounds per gallon = 800 pounds of fuel burned off

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
- 180 pounds
- 240 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

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

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.

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

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.

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.

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

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.

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.