I finally remembered to ask this question about trucks or trailers that lift their axles

Air. Some lift axles are tied to the controls of the suspension, other lift axles have a manual setup that you put up or down,

 

There were some old school tags that were spring up and air down.

 

I've been seeing them more often on new dry vans. I guess it saves wear on one set of tires and makes sharp turns easier?

 

Old school is right. I haven't seen those in years, like 30 years.

 

We have lift control in cab for lifting forward axle on 4 legged,,,lifts fore and aft on 5 legged. You want to be able to lift forward axle when road gets slick or lighten pressure.

 

I ran a spring up/air down until about 1999 because at that time they were lighter than the air/air axles that were available.

 

Also less rolling resistance for much better fuel mileage when lightly loaded.

 

They aren't needed when you're lightly loaded.

 

They can save on the outrageous tolls all too many states like to impose on the transportation industry as well.

 

Our new trucks and tankers that have tag axles work on a weight sensor. No load, axle raises by its self. Lowers when weight is added.