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Position Of The Trailer Tandems

Sliding your trailer tandems toward the front or back of the vehicle will primarily change the weight distribution between the tractor's drive axles and the trailer tandems. Sliding the tandems can also affect the weight on the steering axle, but to a rather small degree. For the purpose of focusing exclusively on positioning the trailer tandems, we're going to ignore the minor changes to the weight of the steer axle. It's rarely a factor when deciding where to place your trailer tandems.

By sliding the trailer tandems forward, you will put more weight on the trailer tandems and take weight off the tractor's drive axles. Conversely, by sliding the trailer tandems toward the rear of the trailer, you will take weight off the trailer tandems and put more weight onto the tractor's drive axles.

Amount Of Weight Moved Per Hole

The trailer tandems lock into place with a set of locking pins that slide into holes drilled into the tandem slider rail. You can see the holes in the slider rail in the picture to the left (click to enlarge).

The distance between the locking pin holes on the trailer will be the main factor affecting how much weight is moved per hole. This distance varies between the different trailer manufacturers, and the larger the distance between the holes, the more weight will be shifted with each 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. This will help you estimate how many holes you'll have to slide the trailer tandems to move the proper amount of weight necessary in order to get the axle weights legal.

Example 1:

You scale your truck at a truckstop and receive your scale ticket. The slider rail hole spacing is 6 inches which will move 400 pounds of weight per hole, and let's assume the steer axle weight won't change. What would you have to do in order to get your truck legal?

• Steer:
  11,590
• Drives:
  34,700
• Trailer:
  32,100
• Gross:
  78,390

In this example, the drive axles are overweight (34,000 pound maximum) by 700 pounds. Assuming each hole in the tandem slider rail moves 400 pounds, you would have to slide your trailer tandems toward the front of the truck a minimum of two holes to transfer enough weight from your drive axles to your trailer tandems in order to get your axle weights legal. The end result would be approximately:

• Steer:
  11,590
• Drives:
  33,900
• Trailer:
  32,900
• Gross:
  78,390

• Steer: remains unchanged for this example
• Drives: 34,700 - 800 (2 holes x 400 pounds each) = 33,900
• Trailer: 32,100 + 800 (2 holes x 400 pounds each) = 32,900
• Gross: Remains the same

Example 2:

You scale your truck at a truckstop and receive your scale ticket. The slider rail hole spacing is 4 inches which will move 250 pounds of weight per hole, and let's assume the steer axle weight won't change. What would you have to do in order to get your truck legal?

• Steer:
  11,320
• Drives:
  31,300
• Trailer:
  35,050
• Gross:
  77,670

In this example, the trailer tandems are overweight (34,000 pound maximum) by 1,050 pounds. Assuming each hole in the tandem slider rail moves 250 pounds, you would have to slide your trailer tandems toward the rear of the truck a minimum of five holes to transfer enough weight from your trailer tandems to your drive axles in order to get your axle weights legal. The end result would be approximately:

• Steer:
  11,320
• Drives:
  32,550
• Trailer:
  33,800
• Gross:
  77,670

• Steer: remains unchanged for this example
• Drives: 31,300 + 1,250 (5 holes x 250 pounds each) = 32,550
• Trailer: 35,050 - 1,250 (5 holes x 250 pounds each) = 33,800
• Gross: Remains the same

So as you can see, this is really simple math. Again, we're assuming the weight won't change on the steer axles for these examples, but in reality it might change a little bit. Most of the time the change in weight of the steer axle will have little or no affect on where you'll put the trailer tandems. The weight on the steering axle is significantly altered by the amount of fuel you have and the position of your 5th wheel, both of which we'll cover soon.