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Methods Of Weight Transfer

To make sure we have the terminology straight, refer to the following diagram:

diagram of a tractor trailer for weight distribution
  • #1 Steer axle
  • #2 and #3 together are your tractor drive tandem axles
    (commonly referred to as "drives" or "drive axles")
  • #4 and #5 together are your trailer tandem axles
    (commonly referred to as "tandems" or "trailer tandems")

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 Most Restrictive Rule Always Applies

When distributing weight across a set of axles, the most restrictive law will ultimately be the limit for any situation. For instance, if the law states that you can carry 20,000 pounds on your steer axle, but your steer tires have a load rating of 6000 pounds each, then you can only carry a total of 12,000 pounds on your steer axle.

Another example would be a situation where you have 35,000 pounds on your trailer tandems, but only 28,000 pounds on your drive axles. Even though you may be able to slide your trailer tandems back far enough to get the weight distribution legal across all axles, if you have to slide them back beyond the legal limit allowed from trailer kingpin to trailer tandems, you will still be illegal. The weight distribution of the load itself would have to be changed in order to get your truck legal in this circumstance.

So you must comply with all the various laws in order to be legal on the highway. We will cover a variety of different scenarios throughout the rest of this section.

Multiple-Choice Questions:

Question #626 (1 of 8)

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Sliding your trailer tandems forward or backward will redistribute the weight mainly between which two sets of axles?

  • Drive axles and trailer tandems
  • Steer axle and trailer tandems
  • None of these answers are correct
  • Steer axle and drive axles
Sliding your trailer tandems forward or backward will redistribute the weight mainly between your drive axles and trailer tandems
You may find a slight change in the weight of your steer axle after sliding your tandems, but it won't be very much and it's rarely much of a concern.
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Question #627 (2 of 8)

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Sliding your 5th wheel will redistribute the weight mainly between which two sets of axles?

  • Steer axle and drive axles
  • Steer axle and trailer tandems
  • Drive axles and trailer tandems
  • Trailer tandems and rear axles
Sliding your 5th wheel will redistribute the weight mainly between your steer axle and your drive axles
Sliding the 5th wheel will generally have little or no effect on the weight of your trailer tandems
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Question #629 (3 of 8)

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

  • The maximum legal length allowed between your trailer kingpin and your trailer tandems
  • The load rating of your drive tires
  • The distance between your steer axle and drive axles or "tractor length rating"
  • 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
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Question #630 (4 of 8)

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You have steer tires rated at 6,150 pounds each, and you're in the state of West Virginia which says the legal limit for the steer axle is 20,000 pounds. What's the maximum legal weight you can carry on your steer axle in West Virginia?

  • 34,000 pounds
  • 12,000 pounds
  • 20,000 pounds
  • 12,300 pounds
When distributing weight across a set of axles, you will ultimately be limited by the most restrictive law for any given situation. For instance, if the law states that you can carry 20,000 pounds on your steer axle, but your steer tires have a load rating of 6000 pounds each, then you can only carry a total of 12,000 pounds on your steer axle
Your steer tires are rated at 6,150 pounds and you have two of them on your steer axle. Therefore you can carry a total of 12,300 pounds (6,150 x 2) on your steer axle. Because you can not legally exceed the load rating of your tires, the fact that West Virginia allows 20,000 pounds on the steer axle doesn't matter. You're ultimately limited by the most restrictive law, which in this case is related to exceeding the steer tire load rating.
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Question #623 (5 of 8)

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In the following picture, what are axles 2 and 3 commonly referred to as?

  • "duals" or "tractor set"
  • "drives" or "trailer drives"
  • "tandems" or "front trailer tandems"
  • "drives" or "drive axles"
#2 and #3 together are your tractor drive tandem axles (commonly referred to as "drives" or "drive axles")
You'll normally hear drivers refer to these two axles as your "drives". They'll say, "The other day I scaled out and my 'drives' were over by 800 pounds".
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Question #625 (6 of 8)

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Which of the following techniques will not change the weight distribution across your axles?

  • Adding or burning off fuel
  • Raising the center of gravity height of the load
  • Changing the weight distribution of the cargo along the length of the trailer
  • Sliding your trailer tandems forward or backward

There are several ways to distribute or redistributing 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 the truck has been loaded. 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.
If you move the center of gravity either toward the front or rear of the trailer, it will change the weight distribution across the axles. But raising or lowering the center of gravity of the load will not change its weight distribution across the axles.
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Question #624 (7 of 8)

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In the following picture, what are axles 4 and 5 commonly referred to as?

  • "trailer drives" or "back tandems"
  • "back set" or "rear tandems"
  • "tandems" or "trailer tandems"
  • "trailer set" or "back tandems"
#4 and #5 together are your trailer tandem axles (commonly referred to as "tandems" or "trailer tandems")
You'll generally hear drivers refer to these axles as simply "tandems". They'll say "The load I had yesterday was loaded incorrectly and I was overweight on my 'tandems' ".
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Question #628 (8 of 8)

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Adding or burning off fuel will mainly change the amount of weight on which axles?

  • Trailer tandems only
  • Steer axle and somewhat on your drive axles
  • Drive axles only
  • Drive axles and somewhat on your trailer tandems
Adding or burning off fuel will mainly change the amount of weight on your steer axle and somewhat on your drive axles
Most of the weight of the fuel will go on your steer axle. The percentage of weight distributed between your steer and drive axles with regard to fuel will depend on the placement of your fuel tanks.
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