Pathetic question about measuring height for ERF

[threeundertwo]

So I'm pretty embarrassed to ask this question but here goes:
DS is almost 3 y.o. (3.5 in December) and rides RF in a Radian XTSL. When he first gets in the seat and is sitting up tall he's right at 1.5 inches from the top of the shell. But when he gets himself comfortable he slouches down a bit and is more like 2 inches from the top of the shell. His head covers up the sun in the logo but I can see the tops of the rays. Before he slouches down the whole logo is covered. He's average height but has a long torso, long neck and large head. Is it time to flip him FF?

 

[Jeni-GAcpst]

I personally go by max height. He may be slouchy 98% of the time. But what happens if he presses against the seat and straightens up just before the moment of impact?
Try grabbing a book or combo of books that are 1.5" thick to place on top of his head. You can press the binding flush against the radian to ensure you're measuring perpendicular to the seat.

Is your son 2.5 or 3.5? If 3.5, I'd feel comfortable flipping him forward.
If 2.5, you might consider the Graco Size4Me aka MySize70 aka Headwise if your son is under 40lb for more RFing. The Graco seats will last about 3 years longer by height - up to a size 8 shirt for RFing. But the RFing weight limit is 40lbs.

 

[threeundertwo]

Thanks for your reply. Sorry for the confusion. He'll be 3.5 y.o. in December. I'll grab a book tomorrow and double check when he's sitting up straight in the radian. I'd been hoping he'd make it to 4 rf, partly because his twin sister will (she's small) and I didn't want to create an issue and don't really want to buy another seat. I know rf is way safer but making it to 3 rf is still pretty good, right?

 

[Jeni-GAcpst]

3.5 years is awesome.

We advocate RFing as close to age 4 as possible due immaturities in the spine. In toddlers, each vertebrae is actually 3 separate bones and paralysis or death occurs when the spinal cord is stretched more than 1/4".
But the bones continue to fuse with age, creating solid rings of vertebrae like the image of a skeleton we are familiar with.

At age 3.6, there's only a 25% chance any separation could be seen in the C3-C7 vertebra.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3256844/
Approximately age 6 has 50% chance of C2 being ossified and approximately age 8 has 50% chance of C1 being ossified.

 

[threeundertwo]

Not sure I measured correctly. Here are a couple photos. The book is 1.6 inches thick. What do you think?

 

[Jeni-GAcpst]

It doesn't look like the pages are flush with the radian. It looks like the book is parallel to the ground.
You want the book perpendicular to the seat: http://www.car-seat.org/showthread.php?t=30201
It looks like if you tip the book so the pages are flush with the seat that he will have a tiny bit of growing room.

 

[TechnoGranola]

Agreed that your book isn't perpendicular to the back of the seat.

I find a DVD case easiest and you can even mark the height on it with a marker that will wipe off the plastic cover after.

Like this (or you can have long side on their head instead, whichever works):

 

[threeundertwo]

Sorry! I totally misunderstood how to measure. If I measure like you showed, he does actually have some room to grow. Yeah! We can hold off on flipping him forward. Thank you! Appreciate all your help.

 

[Jeni-GAcpst]

Great news!