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Sliding The 5th Wheel

On most tractors you can also adjust the position of the 5th wheel to change the weight distribution. Sliding the 5th wheel will change the weight distribution almost exclusively between the steer axle and the drive axles. The trailer tandems will see little or no effect from sliding the 5th wheel. 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 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.

As you can see in the picture above, the 5th wheel slides on rails and is held in place by locking pins through the holes on those rails almost exactly like the trailer tandems. The amount of weight moved per hole will vary between manufacturers, but generally speaking, it's around 500 pounds per hole.

Set It And Forget It

Unlike the trailer tandems, sliding the 5th wheel is something you will rarely do, if ever. The reason is simple - there's an ideal place to set the 5th wheel based on the tractor and trailer combination you're using and there's really no need to move it once it's set properly.

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, a very heavy load, and the trailer tandems set so that the drive tires are as close to 34,000 pounds as possible. 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. Once you get it set, you can leave it alone after that.

Setting The 5th Wheel

We'll go through an example of how the 5th wheel affects your weight, and how to set it up properly.

You scale your truck with a half tank of fuel after getting loaded with a very heavy load and get the following results:

  • Steer:
    11,300
  • Drives:
    34,200
  • Trailer:
    32,900
  • Gross:
    78,400

As you can see, you're overweight on your drive axles, underweight on your steer axle, and just fine on your trailer tandems. Assuming a weight transfer of 500 pounds per hole, you can move the 5th wheel toward the nose of the tractor one hole and you'll get the following result:

  • Steer:
    11,800
  • Drives:
    33,700
  • Trailer:
    32,900
  • Gross:
    78,400

As you can see, sliding the 5th wheel will transfer the weight between your steer axle and drive axles. Now that you've gotten the steer axle as close to 12,000 pounds as you can get it with the drive axles near 34,000 pounds and half a tank of fuel, there's likely never going to be a reason to move it again.

Multiple-Choice Questions:

Question #675 (1 of 6)

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If you slide the 5th wheel toward the nose of the tractor, what will be the effect?

  • You will decrease the weight on the steer axle and take weight off the drive axles
  • You will increase the weight on the steer axle and increase the weight on the drive axles
  • You will increase the weight on the steer axle and take weight off the drive axles
  • You will decrease the weight on the steer axle and it will have no effect on the drive axles
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.
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Question #674 (2 of 6)

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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 trailer tandems
  • The steer axle and the drive axles
  • The steer axle is the only one affected by fuel
  • The drive axles 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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Question #678 (3 of 6)

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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 back 2 holes
  • Move the 5th wheel back 1 hole
  • Move the 5th wheel forward 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.
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 #676 (4 of 6)

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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: 9,800 pounds
    drive axles: 35,100 pounds
  • steer axle: 11,300 pounds
    drive axles: 33,600 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
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Question #679 (5 of 6)

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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

  • Move the 5th wheel forward 1 hole
  • Move the 5th wheel forward 2 holes
  • Move the 5th wheel back 2 holes
  • Move the 5th wheel back 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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Question #677 (6 of 6)

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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: 12,800 pounds
    drive axles: 32,600 pounds
  • steer axle: 11,300 pounds
    drive axles: 34,100 pounds
  • steer axle: 12,050 pounds
    drive axles: 33,350 pounds
  • steer axle: 11,800 pounds
    drive axles: 33,600 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
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