Scale Ticket With Axle and Gross Overloads
At a Pennsylvania weigh station, your 3-axle tractor and 53-foot trailer scale: steer 12,480 lb; drive tandems 33,600 lb; trailer tandems 34,300 lb; gross 80,380 lb. The scale ticket lists common limits of 12,000 lb on the steer axle, 34,000 lb on each tandem, and 80,000 lb gross. Your fuel tanks are full, the trailer is loaded with pallets, and the trailer tandems are currently set near the middle of the adjustment rail. The fifth wheel is in the middle of its slide. You need to leave the scale legally and safely; the next scale is 90 miles away. The weather is dry and the load has not shifted. You have a pallet jack and can remove cargo at the scale if needed.
1. Which axles are over and by how much? Does the gross weight change the solution?
Read the worked answer
Steer is 12,480 lb, over the 12,000-lb limit by 480 lb. Trailer tandems are 34,300 lb, over 34,000 by 300 lb. Drive tandems are 33,600, under 34,000 by 400 lb. Gross is 80,380, over 80,000 by 380 lb. The key judgment is that sliding the fifth wheel or trailer tandems can redistribute weight among axles, but it cannot reduce gross weight. Even if you fix the steer and trailer axle overloads, the combination is still 380 lb over gross. You must remove at least 380 lb of cargo or fuel, or shift load to another vehicle, before leaving the scale legally. The axle adjustments are still needed because the steer and trailer tandems are over.
2. What slider adjustments would you make, and in what direction, to move weight off the overloaded axles? Explain the lever effect.
Read the worked answer
Move the fifth wheel rearward to transfer weight from the steer axle to the drive tandems: the kingpin load acts at the fifth wheel, and moving it closer to the drive axles increases the drive-axle reaction while reducing the steer-axle reaction. Move the trailer tandems rearward to transfer weight from the trailer axles to the drive tandems: moving the trailer axles rearward increases the distance from the kingpin and puts more of the trailer load on the tractor. Make small adjustments, one at a time, because the drive tandems have only 400 lb of room. Do not move both sliders all the way; reweigh after each change. And remember that these moves do not fix the 380-lb gross overload.
3. After adjusting, what must you check before and after reweighing, and what handling effect might the new setting create?
Read the worked answer
Before moving, check that the slider pins are fully engaged and locked, the air lines have enough slack, and the landing gear and trailer components will not contact the tires. After moving, reweigh each axle and gross; the goal is all axles under their limits and gross at or under 80,000. Check tire clearance and trailer tail swing. Moving the trailer tandems rearward can increase offtracking in turns and change the trailer's handling, while moving the fifth wheel rearward can lighten the steer axle and reduce steering traction if you go too far. Test the brakes and make a slow turning check in a safe area. If you cannot get legal with the available slide range, remove cargo.