Why the weight limit for rear facing car seats?

[janellesmommy]

My daughter is 3 years old, and 30 1/2 pounds. I always thought the rear facing weight limit for her Britax Advantage was 33 pounds, but I checked today just in case, and it actually says 30 pounds.

Why is there a rear facing weight limit? I wanted to keep her rear facing as long as possible for safety reasons.

[mightymoo]

I believe that the seat undergoes a lot more stress in a rear facing crash than in a foreward facing crash, which is why the rear facing limit is generally much lower. In a forward facing crash, most of the force is moving away from the seat and on the straps since the body is moving foreward. In a rearfacing crash, most of the force is into the seat as the child's body moves foreward in the car, backwards into the seat. The seat doesn't have anything reinforcing it, so it has to be able to withstand all that force on its own. That's my thinking at least.

[thepeach80]

The old Britax seats are 30# for rfing. They are only tested for that weight. At that weight they know it meets all the safety standards that are required (which for rfing are the seat can't rotate back more than a certain # of degrees). If you wanted to keep her rfing, you could get a Cosco Scenera for $40-$50 and use that till 35# or her head gets w/in an inch of the top.