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Sliding The 5th Wheel

Yes indeed, on most tractors you can also adjust the position of the 5th wheel to change the distribution of weight. 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, quite a bit 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 a fuel, there's likely never going to be reason to move it again.