Top Secrets of Load Control

No More Scales Production and Mouse Scale present: Professionals Should Not Work for Free. Episode 4. Let's settle this once and for all. How do we find the suspension pressure that corresponds to our target axle weight with fewer weighings and dependable estimates?

How does suspension pressure really depend on load? Every word here matters. It is an approximately linear relationship. We carried out thirty weighings across an extended range of suspension pressures to check it. To save you some trips to the scale, we can use the slope-intercept formula. It makes the relationship simpler and easier to see.

Below a trailer's air suspension, there are usually two axles, eight wheels, and the brakes. In our test, these parts weighed about three thousand pounds when suspension pressure reached zero. Wheels and brakes wear out. Sometimes they weigh a little more when the parts are new, sometimes a little less when they wear down. But look at the bigger picture. On many standard two-axle, eight-wheel dry vans, this weight is roughly similar.

It is an approximation, not a measurement of your particular trailer, and usually the weight that interests you is the weight when the load is heavy.

In our test, we raised the trailer body while its tandems stayed on the scale. This extended the range of suspension measurements, so the calculation would not need two calibration weighings and two separate trips to the truck stop. This was a controlled lifting test, not a roadside procedure to copy.

So the pressure comes from the weight supported above the air suspension. For this method, take a calibration weighing with the tandem load above thirty-one thousand pounds while staying within the limits that apply to your equipment and route. Subtract the estimated three thousand pounds below the suspension, then divide the difference by the pressure shown on your gauge.

Now you have the weight change that corresponds to one psi. From there, you can estimate the pressure that corresponds to thirty-four thousand pounds. That is our example target. Always check the applicable axle limits, bridge limits, road rules, and company procedures. To make the calculation easier, please use the free trial in Mouse Scale Light. We don't mind. We are simply giving you a seed of knowledge. In time, it will bring a generous harvest.

The Light version also helps calculate the drive axle suspension parameters using a similar formula with a different baseline for the drive axles. After calibration, you can use the app to estimate axle weights and find a tandem position for the load balance you need.

There is another way to get more useful information from a drive axle pressure gauge. A gauge like this often displays pressure in steps of one psi. If it shows fifty-seven, the actual pressure might be fifty-six point six or fifty-seven point four. The display alone cannot tell you.

For a more precise calibration, start with heavily loaded axles and low fuel within safe operating limits. Suppose the gauge shows fifty-seven psi. Add thirty gallons of diesel and weigh again. In the example we are describing, the drive axle reading increases by about one hundred pounds and suspension pressure by about zero point two psi. That is the change on the drive axles, not the total weight of the fuel. The actual distribution depends on your truck.

Repeat these small fuel additions and certified weighings until the gauge changes from fifty-seven to fifty-eight. Keep track of the measured axle weights at each step.

If your gauge rounds to the nearest whole psi, that change brackets a pressure near fifty-seven point five. The corresponding axle weight lies between the last two weighings. Your persistence and logical thinking can give you a more precise calibration point at fifty-seven point five psi without expensive high-tech equipment.

During those same certified weighings, measure the trailer suspension pressure each time. A suitable handheld pressure gauge with a zero point one psi display step can help.

You now have several pressure readings at approximately the same tandem weight on a level scale platform. Find the average pressure for the trailer suspension at the same tandem weight. But please, for the sake of good driver's common sense, always remember the weighing procedure. Follow the scale operator's instructions and your vehicle and company procedures. Brake force can affect the weighing results. This matters when you are trying to calibrate air suspension properly.

I do not believe in magic or marketing fairytales. Remember what we said at the beginning? Pressure depends approximately linearly on load. We have just explained how to get useful estimates from inexpensive, imperfect driver's gauges. Don't be afraid to learn, but remember where error can come from: the air suspension, uneven ground under the truck, and a driver in a hurry. No fancy scale can fix a ride height valve that is no longer maintaining the correct height.

The height control system on many standard American dry vans is fairly simple. More complex electronic systems also exist.

We, the kings of the road, must go through this process of digitalization from beginning to end to create the best load control system in the United States. Rely on your own effort and your common sense.

If you need two-point suspension calibration, Mouse Scale Pro is at your service. It takes the calculation to another level using all seven important variable parameters of the truck and trailer.

Seven, not one, not two, and not three. The goal is a fuller picture of the truck, the trailer, and the load. Light and Pro are separate apps. Choose the method that fits your work.

In the next episode, Episode Five, we will explain several important load balance options for the driver to choose from.

Mouse Scale, a seed of knowledge. Put it to work for safety, efficiency, and decent reward for professional load control.