Over on Three Axles With Nowhere to Slide
At a weigh station a five-axle tractor-semitrailer reads: steering axle 11,850 lb, drive tandem 34,180 lb, trailer tandem 34,270 lb, gross 80,300 lb. The door plate shows a steering axle rating of 12,000 lb, drive tandem 34,000 lb, trailer tandem 34,000 lb, and a gross vehicle weight rating of 80,000 lb. Tires are rated 6,175 lb each on the steering axle and 5,675 lb each on the tandems. The state gross limit is 80,000 lb. The trailer tandems sit at the 40-foot mark, which is the state maximum kingpin-to-tandem distance. The load is 200 identical sealed cartons loaded nose to tail.
1. List every weight violation and the exact amount over, and state whether any tire is overloaded.
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| Item | Reading | Limit | Result |
|---|---|---|---|
| Gross | 80,300 | 80,000 | over by 300 |
| Drive tandem | 34,180 | 34,000 | over by 180 |
| Trailer tandem | 34,270 | 34,000 | over by 270 |
| Steering axle | 11,850 | 12,000 | legal, 150 lb of room |
| Steer tires | 11,850 ÷ 2 = 5,925 each | 6,175 | legal |
| Drive tires | 34,180 ÷ 8 = 4,273 each | 5,675 | legal |
| Trailer tires | 34,270 ÷ 8 = 4,284 each | 5,675 | legal |
Three violations, not one. Note the distinction: the tandems are over their axle/group rating, but no individual tire is over its rating. That means this is a regulatory overweight, not an immediate blowout risk - which is exactly the kind of detail that gets drivers into trouble, because the officer is writing for the axle rating, not the tire rating.
2. The driver wants to slide the trailer tandems. Explain which direction moves weight which way, and whether any tandem position can fix this load.
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The geometry: the trailer body is carried at two points - the kingpin and the trailer tandems. Sliding the tandems rearward increases the distance from the trailer's center of gravity to the tandems, which increases the share of the trailer's weight carried on the kingpin, i.e. it adds weight to the tractor's drive tandem and removes it from the trailer tandem. Sliding forward does the opposite: it takes weight off the drives and adds it to the trailer tandem.
Apply it here:
- Drives are 180 over → you would need to slide forward to lighten them.
- Forward puts that weight onto the trailer tandem, which is already 270 over - so forward trades a 180 lb violation for a bigger one.
- Rearward would lighten the trailer tandem but add to the already-over drives.
- Rearward is not even available: the tandems are already at the 40-foot state maximum.
The deeper point: sliding tandems redistributes weight; it never changes gross. The gross stays at 80,300 no matter where the tandems sit, so the 300 lb gross violation survives every possible slide. No tandem position makes this legal.
The fix is to remove weight, not move it. Roughly 500 lb off the rear of the trailer drops the trailer tandem by about 300 and the drives by about 200, landing both under rating and gross at about 79,800 - but the driver should reweigh, not trust the arithmetic.
3. The shipper says the load is sealed and suggests either idling for 45 minutes to burn off fuel weight, or taking the county road that bypasses the scale. Evaluate both suggestions.
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Burning fuel: diesel weighs roughly 7 lb per gallon, and a truck idling burns on the order of a gallon an hour. Forty-five minutes of idling removes something like 3 to 4 lb. To shed 300 lb you would need to burn about 43 gallons - most of a tank - and you would still be 180 lb over on the drive tandem and 270 over on the trailer tandem unless the fuel is drawn from tanks mounted between the steer and drive axles, in which case the distribution shifts in ways you cannot predict from the seat. This suggestion fails on arithmetic and on control.
Bypassing the scale: the county road is still a public highway with the same weight limits. You would be illegal on every mile of it, and weigh-in-motion, port-of-entry cameras, and roving enforcement are placed on exactly the roads people use to dodge scales. Deliberately avoiding a scale converts a fixable overweight into an enforcement problem.
What a professional does: break the seal with the shipper's authorization and a witness, remove or redistribute cartons until the vehicle is under on all three limits, get a new weight ticket, and note the seal number change on the paperwork. If the shipper refuses, the freight does not move today. The correct answer is that the load is not legal and the solution is at the dock, not on the road.