By Paul Abelson
senior technical editor
Shootin’ from the hip and eyeballing a load’s weight distribution may get you on the road a little quicker. But overseeing the loading of your trailer and checking the axle weights is the only real guarantee against shooting yourself in the foot and losing time and money.
When my son was hauling steel, he was fined the equivalent of a month’s rent on his efficiency apartment. He was under on his gross weight, but because he eyeballed the placement of the coils he was hauling, he went way over on his rear tandems.
As far as weight distribution is concerned, things are simpler for bulk haulers carrying liquids or dry bulk commodities. Just fill to 80,000 pounds gross combination weight the first time, make the proper adjustments to your fifth wheel slider so you’re at 34,000 on each tandem, and you’re set.
From then on, fill to 80,000 and you’ll be good to go. Many bulk haulers don’t even have sliders. The engineers figure out proper weight distribution and spec the rigs accordingly, saving weight.
For the majority of truckers whose loads vary by size and type, scales play a big part in their lives. Furniture haulers live by scale tickets from scales “certified for use in commerce.” The weight of the load is the basis for their revenue. For others, scales are needed to make sure loads are placed properly.
My son could have avoided his ticket and fine if he had taken the time to use the platform scale at the steel yard. Even though you get just one weight at a time, you can take a few readings and get axle and tandem weights using simple arithmetic.
First, just put the steer axle on the scale. Move up until the tractor’s three axles (steer and drive tandem) are on the platform. Next, get all wheels weighed. You can now calculate weights on each axle set. Tractor minus steer axle equals drive tandem. Gross combined weight minus tractor equals trailer tandem. If you want confirmation, continue across the scale until the tractor is completely off and you’ll have your trailer tandem weight.
If adjustments are needed, have the shipper make them before you leave the yard.
You don’t need to tie down the load as completely as if you were heading into the real world, but even at 10 mph in the yard you’ll want a few well-secured extra straps or chains to go from the loading point to the scales and back. Even if you load on a platform scale, you’ll need to roll back and forth to check distribution, so secure the load for safety. Don’t forget to finish chaining and/or strapping before heading out.
Not every shipper has a platform scale that can handle a complete rig. A few have sectional scales that measure steer, drive and trailer axles separately but simultaneously. Most scales are like those found at state scale houses, with a single platform on which you place your axles in sequence. But no matter how you measure, the results should not exceed 12+34+34=80 (thousands).
The easiest way to avoid going over on any axle is to load using on-board scales. The most popular work with air suspensions, reading pressures needed to keep air bags properly inflated and translating air pressure to weight.
Air-Weigh scales feature digital readout,
and use multiplexing to bring signals from trailers to dashboard readouts. Other models mount on trailers, making it easier to get readings while loading.
Right Weigh makes analog tractor and trailer load scales. The most recent models have direct-reading dial gauges filled with low-viscosity, silicone fluid that prevents corrosion and damps both vibration and pressure spikes. Mounting boxes with clear fronts protect from damage and corrosion.
While tractors are virtually all suspended on air, many trailers still use spring suspensions, especially in vocational applications. Vulcan On-Board Scales makes units using strain gauge technology, measuring loads through deflection in metals. They are designed for dump trucks and packers, but can be effective on lowboys, dump trailers and other steel-spring combinations.
TruckWeight’s Smart Scale brings wireless convenience to loading. Scale readings can be made within a 500-foot radius of the scale, letting a driver ensure that the load is properly distributed or positioned before tying it down. Models for spring suspensions will soon be added to the air suspension line.
Teltek USA offers an on-board system with a lifetime warranty that is designed to read in actual pounds of weight on your air suspension system for tractor or trailer, to the nearest 100 pounds.
Cleral has on-board axle weight monitoring systems for all types of suspensions. The Cleral on-board weight monitoring systems essentially give the accurate weight with a very narrow margin of error.
When installing on-board scales, have them calibrated by weighing on a certified truck scale. Moving and storage company scales are almost always certified, and Cat Scales are checked regularly and certified accurate to closer tolerances than most on-board scales.
Adjustments can also be made using a slider. Moving sliding fifth wheels rearward transfers 200 to 300 pounds off the front axle and onto the drives.
Moving the slider and the trailer forward moves 200 to 300 pounds from the drive tandem to the front axle for each inch of movement. Just six inches of travel can move close to a ton.
Many OOIDA members pull company trailers. They often do not have sliders for trailer tandems. Sliders are also useful when needed to meet kingpin-to-trailer-tandem laws, for maneuvering around tight corners, and for adjusting loads to meet the 12+34+34=80 (thousands) regulation. Trailer sliders add a few hundred pounds and, like fifth wheel sliders, require greasing and periodic maintenance, but they provide added versatility in types of loads you can carry.
Front-to-back balance is important for meeting weight laws. Side-to-side balance is important for safety. Load shifts or improper, imbalanced loading is a factor in rollover crashes, the kind that contribute so greatly to truck driver fatalities.
Offset loads alter vehicle dynamics, compressing springs on one side and unloading springs on the other. During lane change maneuvers or on exit ramps, this imbalance can initiate single-vehicle rollover crashes.
Check your trailer from the rear. If it is not level, readjust the load. Too much weight on tires increases chances of blowouts, builds heat and shortens casing life. LL
Paul Abelson can be reached at firstname.lastname@example.org.