[DRJDVM's '69]

In a head on collision... Or near head on... There is no force on the seat... Your body isn't attached to the seat. The forward movement of the car stops and so does the seat... Your body keeps wanting to go forward and the belt takes that force

In a rear end collision your body is going to put force on the seat back and drive the back mount into the floor and try and pull the front mount up ... At that second the belts aren't doing anything... A split second later they are just keeping you from flying forward and out of the seat

Bottomline is that you don't want anything weak when some massive force may be applied to it