Scale Ticket in Waverly: Under Gross, Over on Tandems
You pull onto the eastbound weigh station on I-80 near Waverly with a 5-axle tractor-semitrailer: a 3-axle tractor and a 53-foot van with the trailer tandems in the forward slider position. The scale reads: steer axle 11,600 lb, drive tandems 32,900 lb, trailer tandems 35,100 lb, gross 79,600 lb. Your steer tires are rated 12,000 lb per axle, and the applicable limits are 12,000 on the steer, 34,000 on each tandem group, and 80,000 gross. The load is pallets of bottled water packed tight against the rear doors with a gap at the nose. The scale master tells you to fix it before you leave. Your trailer tandem slider has 4-inch hole spacing and about 14 inches of forward travel remaining.
1. Which limits are you over, and which are you merely close to? What does the pattern tell you about the load?
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Only one limit is exceeded, but the margins are what matter.
| Axle | Scale | Limit | Margin |
|---|---|---|---|
| Steer | 11,600 | 12,000 | 400 lb under |
| Drives | 32,900 | 34,000 | 1,100 lb under |
| Trailer tandems | 35,100 | 34,000 | 1,100 lb over |
| Gross | 79,600 | 80,000 | 400 lb under |
The gross is legal and two of the three groups are legal - which is why a driver who only looks at gross weight drives away with a citation. The trailer tandem is 1,100 lb over, and the drives have exactly 1,100 lb of headroom. That is not a coincidence: the load's center of gravity is behind the trailer axles, so the trailer axles carry more than their share and the kingpin - and therefore the drives - carry less.
There is a bridge formula side to this too. Even if each group is under its limit, the group formed by the drive axles plus the trailer tandems has its own limit based on the number of axles and the distance between them. Sliding the tandems forward shortens that distance and lowers the bridge limit for that span, so re-weighing after you slide is part of the fix, not an optional extra.
2. How do you decide how far to slide the tandems, and why might sliding alone not be enough?
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Estimate the transfer first, because the drive-axle headroom is small.
- Rule of thumb: on a 53-foot trailer, each inch you slide the tandems transfers roughly 75-100 lb between the trailer axles and the drives. One 4-inch hole is about 300-400 lb. To move 1,100 lb you are looking at roughly 12-14 inches, which is most or all of the travel you have and would put the drives at or over 34,000.
- The fifth wheel is not the answer here. Sliding it forward moves weight to the steer axle, which has only 400 lb of room.
- The load is the real problem. The cargo is packed against the rear doors with a gap at the nose. That is why the trailer axles are heavy. Moving pallets forward puts weight on the kingpin instead of the trailer axles and fixes the cause, not the symptom.
Plan: slide the tandems forward about 8-12 inches to get most of the correction, re-weigh, and if the drives are at 33,800 or the trailer is still over, move pallets forward and re-weigh again. Every iteration is a scale ticket; none of it is a guess.
3. What are your options if sliding puts the drives at their limit, and which do you choose?
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If sliding alone puts the drives at 34,000, you have traded one overload for another - and the bridge formula may still object.
Your options:
- Slide tandems part way, re-weigh, and stop short of the drive limit. Fastest, but it leaves zero margin and a bridge question.
- Move the load forward. With a gap at the nose, shifting several rows of pallets forward moves the center of gravity ahead of the trailer axles: trailer tandems come down, the kingpin and drives go up. This fixes the imbalance and gives margin on both groups. It costs a forklift and time.
- Slide the fifth wheel. Almost no room - 400 lb on the steer.
- Split the load or re-power. Last resort if the freight is simply too concentrated at the rear.
The best answer combines 2 with a little of 1: shift freight forward first, then fine-tune with the slider, then re-weigh and confirm gross, each axle group, and the bridge span before you leave. Leaving with a legal ticket and margin is the job; leaving with a ticket that barely passes is how you get a citation 30 miles down the road after a fuel stop changes the numbers.