Why Your Detachable Car Seat May Not Be Quite as Safe as You Think

— -- For many parents, nothing beats the convenience of a detachable car seat for a very young child. But new data reveals that using it for too long may be putting your most precious cargo at risk.

In crash tests conducted by Consumer Reports, just 4 percent of dummies in rear-facing convertible car seats banged their heads against the seat in front of them. But in rear-facing detachable seats, more than half of the dummies suffered head injuries.

Though the specifics vary by state, infants and young children are required by law to ride in child safety seats. Generally, infants start in rear-facing detachable seats, which include a base and snap-on carrier that mom and dad can remove from the vehicle with baby in tow. Once the tots get a little bigger, they generally switch to convertible seats, which can be rear- or front- facing, have a longer shell, and stay in the car. Most experts recommend that children remain in some type of rear-facing car seat until at least age two.

Based on these tests, Consumer Reports is now recommending that parents switch to convertible car seats by their baby's first birthday – even if the child hasn’t technically outgrown the detachable seat.

"If your child’s getting close to the limits of their rear-facing detachable seat, don’t hesitate," says Jen Stockburger, director of operations at Consumer Reports' Auto Center. "You’re going to buy this convertible model anyway -- we’re just saying, buy it a little sooner."

Just because your child hasn't exceeded the height and weight limitations doesn't mean you shouldn't make the switch, according to Consumer Reports. The dummy "injured" in the crash tests came in at 22 pounds and 29 inches -- well under the height and weight thresholds on the detachable seats that Consumer Reports tested.

Both detachable and convertible car seats are safe, Stockburger clarified -- it's just that after a certain age, convertible seats' longer shells are safer for kids' lengthening frames.

Though the detachable seat's snap-off carrier may be easier for mom and dad, "at age one, safety is probably outweighing convenience," she said.

The Juvenile Products Manufacturers Association said its members "support the efforts by Consumer Reports to provide additional information," but warned that the group's test protocol was "unique" and not required by law. The trade group added that its manufacturers "meet or exceed" government safety regulations.

"Car seats manufactured by our members have a proven track record in protecting child passengers in real world crash situations," JPMA told ABC News.

Bottom line: "Any car seat, even our worst performers, is better than no car seat at all," according to Stockburger.