Drives 300 Pounds Over at the Carlisle Scale - What You Can Actually Adjust
At the weigh station on I-81 near Carlisle, your eight-axle triple set scales: steer 11,000; drive tandem 34,300; lead pup 10,400; first dolly 2,000; middle pup 10,200; second dolly 1,900; rear pup 10,100. Gross is 79,900 pounds. Your steer tires are rated for 12,000 pounds per side and every pup and dolly axle is well under its limit. The lead pup has a sliding axle in its rearmost position with about 10 inches of travel available forward, and the tractor's tandem is at its forward stop. The inspector hands you the ticket and points at the drive tandem. The pups are sealed and you cannot break them to move freight, and your appointment in Hagerstown is in three hours.
1. Which weight limits apply to this set, and exactly which one is violated?
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Four separate limits apply, and you have to check all of them before you decide anything:
- Gross: 80,000 pounds. You are at 79,900 - legal, but with only 100 pounds of headroom. Any adjustment has to leave the total alone, and sliding axles never changes gross.
- Single axle: 20,000 pounds. The pups and dollies at 2,000-10,400 are fine.
- Tandem: 34,000 pounds. The drive tandem at 34,300 is over by 300 pounds. That is the violation on the ticket.
- Bridge formula on short groups: the steer, both drive axles, and the first dolly axle span about 31 feet with four axles. The formula allows roughly 62,600 pounds for that span; you scaled about 47,300. Not an issue here.
The inspector is right: the only violation is the drive tandem. It is small, but 300 pounds over is over, and it is the kind of number that gets worse with a full fuel load or a different pin setting.
2. What adjustment will fix it, which direction, and what must you recheck afterward?
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You need to move roughly 300-500 pounds off the drive tandem onto something with capacity.
Option 1 - slide the lead pup's axle rearward. Moving a trailer axle back increases the share of that trailer's weight its own axle carries and takes load off the kingpin, which is the tractor's fifth wheel and drives. Your lead pup has 9,600 pounds of headroom on its axle, so this is the cleanest move. The hitch is that the slide is described as already at the rearmost position - so verify that before you count on it.
Option 2 - slide the tractor tandem rearward. This unloads the drive tandem and puts the weight on the steer axle, which has about 1,000 pounds of headroom to 12,000.
Option 3 - move the fifth wheel forward on its slider if the tractor has one; same effect, weight to the steer axle.
Recheck: every one of these changes two or three axle readings at once. Re-scale before you leave: drives under 34,000, steer under 12,000, all singles under 20,000, gross under 80,000, and the bridge groups still legal. Then confirm the pup axle is properly locked after the slide.
3. Suppose the gross had scaled 81,200 instead. Would sliding axles have helped? What would you do?
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No. Sliding an axle or a fifth wheel only redistributes weight that is already on the set. The gross stays at 81,200 no matter where the axles sit, so you would still be 1,200 pounds over the 80,000 limit.
What that means in practice:
- The load comes off. Either the shipper takes 1,200 pounds off, or you leave part of it behind. With sealed pups, that is a phone call to the shipper and the broker, not a decision you make with a knife.
- A permit is not a driver's workaround. Overweight permits are arranged ahead of time by the carrier for specific configurations and routes; you cannot buy your way past a scale on the spot.
- Do not run it and hope. Running 1,200 pounds heavy puts the carrier and you at risk, and Pennsylvania scales are not the only place the set gets weighed.
The useful habit: check gross, each axle group, and the bridge groups as three separate questions. Each one has a different fix, and only two of the three can be solved by sliding something.