I learned something new yesterday and I thought I would share it with the world here because it's the first time I heard of such a thing!
You may have noticed all the new cars (2002 and newer) and car seats have this buckle system called LATCH (Lower Anchors and Tethers for Children) My car has LATCH as well as a top tether.
But DID YOU KNOW... These anchors and tethers have a weight limit? The weight limit depends on your vehicle as well as your car seat, whichever is less. My vehicle weight maximums for the LATCH and car seat maximum for the LATCH happen to match at 48 pounds. What this means is, The National Highway Traffic Safety Administration does not test these anchors beyond a 65 pound weight limit (that's a 48 pound child, plus the weight of the car seat) So the LATCH may be safe to use beyond a 48 pound child, it's just not tested so there are no guarantees.
I searched high and low for information on my Britax Wizard car seats about what the weight limit is for the top tether and came up empty handed. My 2008 Ford Escape car owner's manual however did have a weight limit on this top tether of 60 pounds when using a child safety seat and 80 pounds when using the adult seat belt plus a harness. Now I have no idea what this "adult seat belt plus harness" contraption is. I would first assume it might be a 5 point harness booster seat, but then again, that type of seat weighs the same or more than a convertible car seat, so why the 20 pound difference?
I think what all this boils down to is, once your child reaches 48 pounds (or less depending on your vehicle and car seat requirements) you are supposed to use the adult seat belt to secure the child safety seat, in addition to the top tether. Now my question is, is there any harm is using the LATCH as well as the tether AND adult seat belt? Does that cover all my bases or does that catapult my child from the car in the event on an accident? It's all very confusing!