Joie bay latch SI Harness-to-Booster Preview
A few weeks ago, Joie entered the combination harness-to-booster seat market with the bay latch SI. They surprised us all with a soft launch—it just appeared one day to everyone’s delight. This is a category of car seats begging for more representation: few exist with tall enough harness slots to get kiddos to belt-positioning booster seat age. The bay latch SI and the bay latch SI plus meet that need with flair.
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WEIGHT AND HEIGHT LIMITS:
Forward-facing: 30-65 lbs., 27-49”, at least age 1
Highback booster: 40-100 lbs., up to 57”, at least age 4
Backless booster: 50-120 lbs., 43-60”, at least age 4
BAY LATCH SI FEATURES:
Rigid LATCH attachments
Can install with rigid LATCH and seat belt at same time, if vehicle allows
Seat belt lockoff
Compliant with newest FMVSS 213a and 213b safety standards
4-position adjustable seat depth
Optional 7-position footrest (included with bay latch SI plus)
15-position no-rethread headrest
AutoClick™ magnetic chest clip
Two removable cup holders
On-board harness storage for booster mode
Machine-washable fabrics
10 yr lifespan before seat expires
FAA-approved in harness mode only
Follows NHTSA crash replacement guidelines
Made in China
MSRP $239.99 in 2 fashions for bay latch SI (Mocha and Shale)
MSRP $269.99 in Shale for bay latch SI plus
MEASUREMENTS:
Harness height: 12”-18 ½″
Shoulder belt guide height: 22”
Width between side impact insert bolsters: 10”
Shoulder width: 13 ½”
Crotch strap depth: 5”-6” (one slot, but changes depending on seat pan depth)
Seat depth: 15”, 15 ½”, 16”, 16 ½”
External widest point: 19 3/8”
Seat weight: ~23 lbs. with harness; 8.8 lbs. as backless booster
INSTALLATION:
We’re still working on installing the bay latch SI in different vehicles, but so far installation is a rigid LATCH dream! Click, click and you’re done. Rigid LATCH tightly couples a car seat with the vehicle’s lower LATCH anchors with very little effort (usually the effort goes into moving the upholstery out of the way). Because it provides a such a secure installation, we like to think of it as a great safety feature: when your car seat is installed with rigid LATCH, it definitely moves less than 1”.
Joie allows adding the seat belt with rigid LATCH on the bay latch SI if your vehicle also allows it. Always double-check your vehicle owner’s manual in the Child Restraints section to see if you can use both for installation.
LATCH Weight Limits
Forward-facing LATCH weight limit: 40 lbs.
After your child reaches 40 lbs., you can add the seat belt or, if your vehicle doesn’t allow the addition of the seat belt to the LATCH installation, switch to a seat belt installation. The bay latch SI installed quite easily using the seat belt in my Tesla Model 3 in both the outboard and center seating positions—something that both pleased and shocked me because nothing installs easily in that car.
Installed with rigid LATCH, seat belt, and tether
Installed with seat belt, lockoff, and tether
The finicky Tesla head restraints didn’t pose a problem either. There was definite contact with the bay latch SI headrest, but it wasn’t pushed out of position and could easily be moved up or down.
The only issue I can see so far is with the sloping roofline of the Model 3. When the bay latch SI headrest is in its highest positions, it does make contact with the roofline, which is not allowed in the manual (and is from where the side curtain airbags drop in a side impact, hence the warning in the manual).
When this happens, I would convert to backless booster mode
Conversion to booster mode, both highback and backless, is easy. I did find it easier to buckle in the Model 3 since the buckle in the Model X was right up against the base.
The latchplate is smashed against the booster seat and must go into the buckle parallel to the booster. It’s . . . difficult.
Here’s a preview video we took at the 2026 Kidz in Motion Conference highlighting the features: