TIPS FOR TRUCKERS: Weight & Balance

Simple Planning Can Save the Day

Just a simple calculation of diesel fuel weight and some trip planning can save the day.

Generally speaking, a driver should be familiar with his equipment and his axle weight — especially when calculating loading and fueling.

Allowable Weight on the Axles

In the United States, on a five-axle set-up, 80,000 lbs is the gross weight allowed — with a maximum of 12,000 lbs on the steering axle and 34,000 lbs on the drives and trailer axles. Ten feet or greater spread axles are allowed a total of 20,000 lbs on the spread — but still no more than 80,000 lbs gross max.

Most new drivers don’t pull spread axles — so we’ll stick to the 12,000-, 34,000- and 34,000-lb set up for discussion’s sake.

Where are Your Fuel Tanks?

When fueling, diesel weight will primarily ride on either the steering axle or the drives, depending on the location of the tractor’s tanks.

Most drop-nose rigs carry their tanks far forward on the frame — under the cab doors, whereas most long-hood conventional trucks carry their tanks under the bunk. Obviously then, when a long-hood truck takes on fuel, most of the additional weight will ride on the drive axles.

Leave Room for Fuel!

For this reason, in addition to the load over the steering and trailer axles, a long-hood truck driver must account for the effect of fuel weight over the drive axles when calculating his remaining allowable weight.

Far too often, new truckers will forget to consider the weight of the fuel — and on which axle group it sits — when calculating the overall weight of the load.

Of course, this is different for each big rig truck and changes with each load.

For example, with 80,000 lbs allowed, a truck driver wants his steering axle weight at no more than 12,000 lbs and his trailer as close to 34,000 lbs as possible; this combination allows him a 31,000 lb drive axle weight and leaves a 3,000 lb ‘buffer’ for fuel; 3,000 lbs is more than enough allowable weight to fuel virtually any highway big rig.

So How Much Does a Gallon of Diesel Fuel Weigh?

As diesel gets colder, the density increases, and the energy a gallon contains and potential MPG the fuel can achieve increases with it. Alternatively, as the temperature rises, the density and potential MPG decreases.

Though the weight varies somewhat with temperature and other factors, the difference is minimal. A US gallon of diesel fuel weighs 7.1089 lbs, but for easier math it’s safe to calculate at 7 lbs even or 700 lbs for one hundred gallons.

A typical over-the-road truck will hold anywhere from 200 to 300 gallons of diesel fuel. Quickly calculating, then: 200 gallons of fuel at 7 lbs/gallon adds 1400 lbs to the load — 300 gallons adds 2100 lbs and so on. Average fuel economy depends on several factors: the size of the load, whether you’re pulling a flatbed trailer or van trailer, the shape of the tractor hood (flat-hooded Peterbilt 379 model vs the more aerodynamic Kenworth T-2000, for example) and engine model. Some truckers claim they get 7 MPG at times — but that’s pretty high; average is about 5 to 6 MPG [source: Yahoo].

Plan Your Fuel Stops

Occasionally a new driver will scale his rig after loading, see the weight is under the legal gross allowable, and head happily on his way to fuel up — only to be ticketed for being overweight at the next scale.

It’s worth remembering:

· If you plan your route of travel ahead of time, the scales won’t take you by surprise;

· If you’re close to your legal weight limits, don’t take on fuel just before entering a weigh scale.

A few minutes spent on road trip planning will prevent big overweight fines and a lot of headaches!

Watch for my next article on Weigh Station Bypass Service!

Alkane thanks Catherine, editor of Smart-Trucking, and for the content of this article.

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