Scale Ticket and Trailer Tandem Slide Decision
At an Ohio weigh station, your 5-axle tractor-trailer scales: steer axle 11,800 lb, drive tandems 33,200 lb, trailer tandems 34,600 lb. Gross is 79,600 lb. The trailer tandem is set in the fourth hole from the rear. You need to move weight off the trailer tandems without overloading the drives. The scale house is open, and you can slide the tandems. The trailer has 10 holes spaced 4 inches apart; each hole changes the trailer tandem weight by about 400 lb and the drive tandem weight by the opposite amount. The steer axle changes little. The trailer tandem limit is 34,000 lb, and the drive tandem limit is 34,000 lb. Your fuel tanks are full, and you have 200 lb of chains in the tractor.
1. Which axle group is over limit, and by how much? Is the gross weight over?
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Trailer tandems: 34,600 minus 34,000 equals 600 lb over. Drive tandems: 33,200 is 800 lb under the 34,000 limit. Steer axle: 11,800 is 200 lb under a 12,000 lb limit. Gross: 79,600 is 400 lb under 80,000 lb.
So only the trailer tandems are over, by 600 lb. The gross is legal, and the drives have room to accept weight. That means a tandem slide can fix the problem if you move the right number of holes and reweigh.
2. How many holes should you slide the tandems, and in which direction? Show the arithmetic.
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You need to remove at least 600 lb from the trailer tandems. Each hole forward shifts about 400 lb from the trailer tandem to the drive tandem.
One hole forward: trailer 34,600 minus 400 equals 34,200 lb, still 200 lb over. Drives 33,200 plus 400 equals 33,600 lb, legal.
Two holes forward: trailer 34,600 minus 800 equals 33,800 lb, legal. Drives 33,200 plus 800 equals 34,000 lb, exactly at the limit.
So slide the tandems two holes forward. Because the drives end up exactly at 34,000 lb, you must reweigh rather than trust the estimate. If the actual shift is less than 400 lb per hole, two holes may not be enough; if it is more, the drives may go over. Sliding forward also shortens the trailer wheelbase, so check the bridge formula on the new scale ticket.
3. After sliding two holes forward, what could go wrong, and what checks do you make before leaving the scale?
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The main risk is overloading the drives. At 34,000 lb they have no margin, and any fuel added later, load shift, or inaccurate estimate could put them over. Sliding forward can also change the bridge formula calculation because the distance between the drive tandems and trailer tandems is shorter. Check that the pins are fully locked, the air lines are not stretched, the tires clear the frame, and the mud flaps are not trapped.
Then reweigh all axles and the gross. If the drives are at or over 34,000 lb, slide one hole back or adjust the load. Also confirm the trailer tandems are not so far forward that the rear overhang or turning path becomes a problem. Do not leave the scale on a verbal estimate; the ticket is the proof.