air weigh on board scales

The dial gauges work, and will get you by in most circumstances as everyone has said. If you need something more accurate, you could do like I've done and remotely (for accessiblity) install a schrader valve and line (same end as a valve stem--auto parts stores will carry them) that is connected to the air suspension. Purchase a digital tire pressure gauge that reads to the tenth of a pound per square inch up to like 160.0psi. The items are readily available and much cheaper and easier to install than the air weigh or dial guages. All you then need is to figure out some mathematics to get your exact weight. I'll explain...

The formula I use is this...

p(x) + U = W where: p = air bag pressure in psi
x = variable weight factor (it's the amount of weight lifted per psi in the air bags)
U = unsprung weight (ie, axle & tire weight--the amt of weight not being supported by the air bags)
W = total axle group weight

You will need to solve the formula to obtain your unsprung weight (U) and the variable weight factor (x). You do this by obtaining the axle group weight and psi for both empty and loaded states. As an example:

p = 5.6 psi; W = 9240 lbs (axle group empty)
p = 66.3 psi; W = 34,280 lbs (axle group loaded)

Now we solve for x:
5.6(x) + U = 9240 & 66.3(x) + U = 34280
U = 9240 - 5.6(x) & U = 34280 - 66.3(x)
therefore: 9240 - 5.6(x) = 34280 - 66.3(x)
9240 - 5.6(x) + 66.3(x) = 34280
-5.6(x) + 66.3(x) = 34280 - 9240
60.7(x) = 25040
60.7(x)/60.7 = 25040/60.7
x = 412.52059

Now, solve for U:
5.6(x) + U = 9240 ...we'll use our x that we just derived
5.6(412.52059) + U = 9240
2310.1153 + U = 9240
U = 9240 - 2310.1153
U = 6929.8847

Now the driver has a formula to obtain his/her weights at any pressure he/she obtains with the digital tire gauge. This is very accurate if the guage is consistent. However, it does not compensate for atmospheric conditions.

For example, the driver gets a suspension pressure reading of 48.3 psi using the gauge...
48.3(412.5) + 6930 = U
U = 26,854 lbs

If you keep track of your periodic scale weights and the corresponding suspension pressure measurements, then you can keep your formula "calibrated". The process may seem complex, but it's very do-able. Now, who said that you'd never use that high school algebra?

 

Gezus... gonna have a tough time topping that one...

 

Just trying to help as I feel it accomplishes everything I need, and there's more than one way to skin a cat. I will say this though, it's still much simpler than trying to keep up with a log book and hours of service. ...or how 'bout that bridge law formula?

 

My brain hurts.....

 

Hi again AgLaw: Your gonna put Cat Scale out of business...
seriously , good for you, on taking the time and having the pride to "do it right"