Seat belt question

Hi! I’m shopping for a car and I’ve got stacks of specs & details. There’s one thats puzzling me. What are seat belt pretensioners and load limiters? What do each of them do? And why is it that almost all cars I’ve seen have them on the front 2 seats but not for the backseat passengers? Does that make the backseat passengers less safe? Thanks for your help!

seat belt pretensioners are only used up front since the air bags are up front. They are not used for the rear since there are no rear seat air bags. When the air bags blow the pretensioners lock seat belts. On some vehicles the p/t is in the belt retractor and on others it is in the buckle assm (on those, the buckle assm gets sucked down a couple of inches).

After the impact the left seat belt is loose and the retractor will not operate to take the slack up. On the rt belt it is the same unless the seat was not occupied. In that case the belt will be so tight you can pluck it and it will produce a noise.

The pretensioners work through an explosive charge, much like the airbag does. They have to be replaced when fired, probably the whole seat belt retractor along with it. They probably work to make the airbag safer by positioning the person better, holding him in the right place.

A load limiter is used to reduce seat-belt related injury. Simple ones are stitch a fold in the belt, when a forcefull collision happens, the threads break, releasing a little more belt. Advanced ones use a torsion bar to do the same thing.

The rear seat passengers probably don’t need pretensioners when there are no airbags. Load limiters are probay left off the car to save money or because there are less things in the rear that will injure passengers.