For a moment, empty your head of the frustration of yet another axle-weight violation and imagine a simple pair of sawhorses, the type you’d have in the garage at home. Picture a 10-foot plank resting evenly across them, so each sawhorse supports half the plank’s weight. Now, smack-dab in the middle, plunk down a 10-pound box of nails. Presto: each sawhorse has to support more weight, but the pounds are distributed evenly, fifty-fifty. Shift the box of nails toward one end of the plank and the sawhorse that’s closest to the box will take on more of the load. Tuck another sawhorse under the plank and the dynamics change again.
This is the basic tenet of weight distribution when you load your trailer. You can picture how varying the weight of the payload and changing its position along the frame will alter the amount of pressure that goes on each axle. Indeed, you don’t have to imagine any of this stuff: you can calculate weight distribution among axles with a basic mathematical formula. That’s how the guy you bought the trailer from does it, with help from software that factors in various payload and vehicle configurations to make sure your spec is right for the job. That sawhorse-and-plank setup, for instance, is the wheelbase of your vehicle.
If only it were that simple when you’re at the dock. It’d be easy to load a truck right to the pound if you had the dealer’s computing power always at hand, but when it’s just you and your wits, you’re stuck trying to eyeball the load to the legal maximum.
Knowing how to load could save you a bit of dough on your next trip across a scale or when spec’ing your next truck or trailer. It can also make a huge difference–like, 5,000 to 10,000 pounds–in regaining lost payload capacity, says Ray Camball, manager of fleet sales at Trailmobile Canada. You may think that distributing the weight evenly from front to back in the trailer will balance the weight borne by the drive and trailer axles, he explains, but that’s rarely the case. Splitting the weight evenly on either side of the trailer’s mid-point may actually put a larger portion of the load’s total weight on to the trailer axles. Knowing where to “centre” your load on the trailer can be the difference between a legal load and an overweight fine.
Before you eagerly start mapping out load placements, consider the many factors that affect payload capacity and weight distribution. Trailer kingpin placement is one of the most significant; most multi-axle trailers have shallow pin placements–24 inches or less–while the lead trailer of a set of B-trains will have a deeper kingpin setting. Around 42 inches is common but some are as deep as 60 inches or more. The shallower setting causes more of the weight to ride on the trailer axles, which is just what you want in a tri- or quad-axle application. The deep setting on a B-train lead, on the other hand, is designed to keep the weight on the tractor and off the centre axle grouping. Often, the pup has a very shallow setting, intended also to keep the weight off the centre axles by letting the pup tandem do most of the work. This is especially true in the case of a seven-axle train, while it’s not so much of an issue with the eight-axle combinations.
“The 36-inch kingpin setting typical of 53-foot trailers is a compromise, and a throwback to the era of 48-foot trailers,” says Camball. “The 36-inch pin worked well with the 48-footers, but the 53-footers really should have a 42-inch pin setting. When 53-foot trailers were introduced, a few jurisdictions had old regulations on their books limiting the kingpin to 36 inches and we pretty much decided to live with it rather than go through a long, tedious process of convincing them to change their rules.
“Now we have to compromise by placing the centre of the payload [weight-wise] ahead of the centre line of the trailer to overcome the effects of the ‘wrong’ kingpin setting,” he says. By loading ahead of centre, you remove weight from the trailer axle and place it toward the front where, by sliding the fifth wheel forward, you can shift more of the load to the steer axle.
There are obvious limits to the weight one can stuff onto a trailer; your payload will be dictated by your gross combination weight limit (GCW) minus the tare weight of the truck and trailer. One way to coax a little more capacity out of your trailer is to spec the lightest unit possible–using fewer crossmembers or vertical posts, for example, or a lighter pick-up plate.
But by making better use of your existing carrying capacity, Camball says, you can afford to spec a heavier, more durable tractor-trailer combination. While a few overweight tickets may have you leaning toward a lighter spec, learning how to load the truck properly could be a wiser, less expensive alternative.
Camball shows as much with the chart on page 47.
It illustrates how much payload capacity you can pull out of tractor-trailer combinations simply by loading them properly. As you see with unit #12, spec’d for U.S. weight limits, switching from steel to aluminum wheels and hubs and low-profile tires wouldn’t make up one-quarter of the difference gained if you just shifted the freight forward a couple of feet.
The same applies to overweight fines: look at your tickets to see where you’re heavy and adjust your loading strategy to overcome the problem. Of course, if you’re over gross, there are some other adjustments you’ll have to make, which we can’t help you with.
The tractor-trailer itself will have an impact on weight and balance, of course, so know the tare weight of your unit. When you axle-weigh the truck empty, make sure the truck is ready to run–fill the tanks and put a driver on board. Set the centre of the trailer bogie to the 41-foot position and slide the fifth wheel to the appropriate spot (eight inches ahead of centre with a 50-inch set-back front axle, 12 to 14 inches ahead of centre with a set-forward axle).
You’ll notice that the empty vehicle weights presented in Camball’s chart vary only slightly, but the way the trucks are configured can affect payload by up to 10,000 pounds. This chart takes empty-unit weights, potential payload, load placement, and fifth-wheel placement into account when calculating loads for steer, drives, and trailer axles. Camball’s computer simulations are based on straight mathematical calculations and have been proven time and time again in the field as the weight and measurement info is provided correctly.
Unfortunately, the only way to determine actual axle loads, short of using a computer program, is trial and error. Camball’s modeling will work only if your truck is exactly like the one he uses in the chart, and if the load is the same weight. However, the principles can serve as good guidelines.
Notice how even a minor deviation can produce dramatic results. Compare lines 12 and 14: the units weigh the same, the fifth-wheel placement is the same, and trailer bogies are both centred at 37 feet. The steer- and drive-axle weights on #12 are way below maximum, but the trailer axle is loaded right to 33,978 because the load is too far to the rear. In #14, the load centre is placed 67.5 inches ahead of centre, shifting a lot of weight to the tractor axles. The trailer axles are actually slightly lighter.
Compare units 11 and 12 on the chart. Everything is the same except the bogie position–#11 is stretched out to 41 feet, while #12 is shortened to 37 feet. Both loads are positioned at centre, yet #11 could be loaded 5,100 pounds heavier if the bogie were pulled back.
Now look at units 10 and 11. Everything is the same except the load position: #10 is centred 26 inches ahead of the van centre line, while #11 is sitting dead centre in the middle of the trailer. By leaving the load that far to the rear, the trailer axles max out at 33,977 pounds, leaving the drive and steer axles well under maximum. Push the load centre forward, as in #10, and you move the weight off the trailer axles and onto the other axles. The gain for having moved the load just a couple of feet ahead is 4,300 pounds.
Before loading a trailer, following these guidelines, you’ll need to stake out the mid-way point of the van before you decide how far ahead of centre to place the load. If there weren’t enough room between the load centreline and the nose of the trailer, double-stacking pallets in the nose would produce the same effect as extending the load four feet ahead of the front wall of the trailer. If you need empty space (weight) in the nose of the van, as you might in the front of a B-train pup, stand a couple of empty pallets on end to brace the load against the front wall.
There are certain principles you can safely stick to, assuming you’ve got a modest-wheelbase tractor with a 53-foot van using a 36-inch kingpin (the brand of equipment is irrelevant, provided that the spacing and spreads, tare weights, and kingpin placement are the same):
w When running a tractor with a 30-inch front-axle position, keep the fifth wheel about 12 inches ahead of centre.
w When running a tractor with a 50-inch front-axle position, keep the fifth wheel about eight inches ahead of centre.
w Keep the trailer bogies at the 41-foot mark.
w Running to U.S. weight limits, the centre of the payload should be at least 24 inches ahead of the centre of the van.
w In Canada, the centre of the payload should be at least 28 inches ahead of the centre of the van.
w Because you gain some flexibility in the front when you have a sliding fifth wheel, vans should be loaded with the centre of the payload anywhere from two feet to five feet ahead of the centre of the van.
Those are rules of thumb. If you really want to know how much weight you’re hauling, and how that weight is distributed, head to an axle scale. You may find that you typically run light on the steer axle, light on the drives, but heavy on the trailer. This suggests the weight is sitting too far back in the trailer. If you’re heavy up front and light on the back, the weight may be too far forward.
This isn’t fiddling around. The difference between the lightly loaded axle and its maximum carrying capacity is lost payload potential that could be accommodated by simply rearranging the freight. Being aware of how the weight is distributed “naturally” is the first step toward learning how to position the weight where it should be to stay legal and to maximize capacity.
Call it art, science, or a pain in the butt, weight and balance are things every truck operator has to deal with, and the penalties for screw-ups can be substantial. If a cash fine isn’t enough, try walking several dozen 100-pound bags of onions from the back of the trailer to the front to redistribute the weight.
That’ll learn ya, real quick.Calculating axle loads is a black art to say the least when you’re eyeballing pallets on the dock. But a Canadian company says it’s found a way to help you conjure up weight and dimension patterns that work. Cie-Tech of Brossard, Que., is the developer of Load Xpert, software that lets you easily calculate axle-load distribution for almost any vehicle configuration. Most programs that make similar claims are basically spreadsheets, but Load Xpert’s graphical interface shows you the impact of shifting freight or components around using diagrams of tractors, trailers, and combination units. After you provide specifics about the equipment you’re using and the load itself, be it a full load or individual skids, you can use your mouse to click on axle groups, lift axles, your fifth wheel, or payloads and drag them around while the program automatically calculates whether you’d be running legal. The software also tells you the vehicle’s centre of gravity as you’re designing your load-perfect for dealing with those 50,000-pound steel coils that take up only four feet of the flatbed.
Once you’ve assembled a legal load on screen, you can print out a detailed report with the total unit weight, broken down by tractor and trailer, per axle group, by compartment if necessary, and the distances between them all.
The software won’t solve all your problems, though. Cie-Tech sales and marketing director Jacques Healy says there’s a garbage-in/garbage-out principle at work: “The software is only as good as the information you enter,” he explains.
Load Xpert is aimed mainly at the truckload sector, but that hasn’t stopped Rick Miller, operations manager at MacKinnon Transport in Guelph, Ont., from using it for less-than-truckload freight. If you have all the necessary data for each skid, you can literally build the load as you’re putting it onto the trailer, Miller notes, adding he can assemble a load on Load Xpert and come within 20 pounds of the reading taken at a scale. “It does take a lot to get that up and going,” he admits. “There’s a lot of information to gather, and a lot of precise measurements.”
Load Xpert uses the Windows 95, 98, or NT operating system and is available in four versions: Load Xpert Pro, for truck and trailer manufacturers, dealers, repair shops, and leasing companies; Heavy Haul and Permit, for heavy-haul vehicles with drop-deck trailers, jeep dollies, booster axles, and bridge beams; Fleet, which gives dispatchers and shippers step-by-step guidance to the best loading patterns for identical and non-identical loads; and Tanker Fleet, which calculates fill volume patterns for single and multi-compartment tank vehicles.The “centre” of the load refers to the point at which it would balance if it were on a teeter-totter–e.g. 23,000 pounds at the front of the centre point, and 23,000 pounds at the rear of it. Of course, the real centre point may not be the actual middle of a row of pallets, especially if the load is mixed and of varying weights. You or your drivers can make life easier by arranging the load prior to filling the trailer so as to keep it as evenly balanced as possible. If that’s not an option, load the heavier pallets first but try to maintain a maximum floor loading of about 900 pounds per foot of trailer length. That would see two pallets loaded side by side, weighing a total of 3,600 pounds. It’s hardly scientific, but at least you’ll get a relatively even load from front to back.
Putting the weight-centre of the load over the centre line of the trailer may seem obvious, but it usually results in overloaded trailer axles. Referring to lines 3, 4, 5, 11, and 12 on the chart below, you can see how centring the load would produce an overload condition on the trailer axle if the payload hadn’t been cut back way below normal.
Shift the centre of the load weight back from the centre line and you risk overloading the rear axles. Referring to line 15 of the chart, you can see that the payload has to be reduced by almost 10,000 pounds because the rear axles are nearly maxed out.
By shifting the load forward, you’re taking weight from the trailer axles and putting it over the kingpin, which transmits weight to the tractor via the fifth wheel. The position of the fifth wheel dictates how the weight is divided among the drive and steer axles. We know that the 36-inch pin setting is a bit shallow for the geometry of a 53-foot trailer. So we need to compromise by loading a little more weight into the nose of the trailer. Referring to the column that shows payload centre-line placement, see how the farther forward the centre of the load moves, the more the weight is shifted to the steer and drive axles.
Tractor Fifth wheel Trailer Bogie C/L Payload Payload C/L Calculated axle weights Gross
weight ahead C/L weight from kingpin weight ahead of van C/L Steer Drives Trailer weight
#1 19,600 lbs. 11 in. 14,800 lbs. 41 ft. 56,900 lbs. 27 in. 11,944 lbs. 39,675 lbs. 39,681 lbs. 91,300 lbs.
#2 19,400 lbs. 12 in. 14,800 lbs. 41 ft. 57,100 lbs. 28 in. 12,054 lbs. 39,577 lbs. 39,669 lbs. 91,300 lbs.
#3 19,600 lbs. 12 in. 14,800 lbs. 41 ft. 51,400 lbs. 0 11,740 lbs. 34,409 lbs. 39,651 lbs. 85,800 lbs.
#4 19,600 lbs. 12 in. 14,800 lbs. 37 ft. 45,800 lbs. 0 11,545 lbs. 28,524 lbs. 39,631 lbs. 79,700 lbs.
#5 19,600 lbs. 12 in. 14,800 lbs. 41 ft. 41,500 lbs. 0 11,431 lbs. 30,492 lbs. 33,977 lbs. 75,900 lbs.
#6 19,600 lbs. 13 in. 14,800 lbs. 41 ft. 45,200 lbs. 24 in. 11,707 lbs. 34,000 lbs. 33,893 lbs. 79,600 lbs.
#7 19,600 lbs. 12 in. 14,300 lbs. 41 ft. 45,600 lbs. 24 in. 11,706 lbs. 33,978 lbs. 33,816 lbs. 79,500 lbs.
#8 19,600 lbs. 13 in. 14,300 lbs. 41 ft. 45,800 lbs. 25 in. 11,879 lbs. 33,993 lbs. 33,828 lbs. 79,700 lbs.
#9 19,600 lbs. 13 in. 15,100 lbs. 41 ft. 45,000 lbs. 25 in. 11,876 lbs. 33,956 lbs. 33,868 lbs. 79,700 lbs.
#10 19,200 lbs. 14 in. 14,300 lbs. 41 ft. 46,300 lbs. 26 in. 11,868 lbs. 33,938 lbs. 33,995 lbs. 79,801 lbs.
#11 19,200 lbs. 14 in. 14,300 lbs. 41 ft. 42,000 lbs. 0 11,503 lbs. 30,020 lbs. 33,977 lbs. 75,500 lbs.
#12 19,200 lbs. 14 in. 14,300 lbs. 37 ft. 36,900 lbs. 0 11,098 lbs. 25,354 lbs. 33,978 lbs. 70,430 lbs.
#13 19,600 lbs. 14 in. 14,300 lbs. 38 ft. 45,000 lbs. 48 in. 11,688 lbs. 33,750 lbs. 33,462 lbs. 78,900 lbs.
#14 19,200 lbs. 14 in. 14,300 lbs. 37 ft. 46,300 lbs. 67.5 in. 11,871 lbs. 33,976 lbs. 33,953 lbs. 79,800 lbs.
#15 19,200 lbs. 14 in. 14,300 lbs. 41 ft. 36,900 lbs. -39 in. 11,067 lbs. 25,353 lbs. 33,979 lbs. 70,399 lbs.
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