trailer suspension

I'm amazed how airbags have simplified suspension on today's trailers.
As a kid, our trailers had skinny shackel springs with helper springs on top.
Nobody's trailer ever tracked true resulting in poor tyre wear, usually caused from loose "U" bolts and then a sheared centre bolt which allowed the axle to wander about.
The old man made his axle alignment adjustable using a plate bolted under the spring and located via the centre bolt on top and adjusting bolts pressing against the axle below.
So to adjust the axle, you'd loosen the "U" bolts and push the axle forwards or backwards with the threaded bolts. Then everything was tightened up and I got to drive (12) while dad followed in the ute to see how she tracked.
Just when he thought he could make a fortune with his idea, free shackel springs with track rods became the norm.
So it was out with the oxy and we cut off the spring hangers etc and copied the modern idea.
Loved, it, no more greasing the trailers.