Tanker axle group over weight?

Hey, not to jack this thread but here's a question. Here in Washington state I run a rocky mountain A train. My weight runs around 105 to 105,700 and my tandems are at around 32. Why won't they let me axle out my weight? It doesn't make sense to me. Why does it matter?

 

We haul dry bulk cement and ash. Loaded on a platform scale, you will almost always be over on your drives if your gross is 79k or more.

If I know I have a scale or two to cross, I’ll load to only 77k (still gives me 25 tons in the trailer) and knock some of the weight to the trailer axles before I hit the road. You have to do this right after loading while the cement is still kind of fluffy. Once you get rolling a while, it will settle and you won’t be able to move it much.

 

Changing fifth wheel position does not take all the weight off the drives and put it onto the rears

 

In my experience a driver is more likely to be over on the drives than on the tandems. I guess the only exception to this would be if the truck has a high fifth wheel.