The chains used on the Car Ferry were wrapped around the four inflated tyres, which should have provided a degree of shock-loading for the chains themselves.
Having each wheel firmly fastened to the aircraft meant that the rest of the vehicle could move, but only within what its suspension (its own springs and shock absorbers) allowed, a matter of inches, only UP or DOWN. Lateral or fore and aft movement of the vehicle was made impossible.
I have forgotten, if I ever knew, what was the strength of the tie down points, but the Bristol Freighter 170 Mk32 had been made specially for this work. We carried a lot of cars over the years.
The weights at Bagram WERE very different.