Cybex Sirona S
Cybex Sirona S
Convertible Car Seat
Convertible Car Seat

The best car seat is the one that fits your child, vehicle, budget, and lifestyle and has the features important to you. The safest car seat is the one you can install correctly and use properly on every ride! Let us know in the comment section what questions you have about this review of the Cybex Sirona S convertible car seat.

Cybex Sirona S Car Seat Review (USA/Canada)

In the realm of car seat safety, the Cybex Sirona S stands out as a unique and innovative option for parents and caregivers in the USA and Canada as it was the first convertible car seat with a load leg. This car seat offers a swivel feature, making it exceptionally convenient for rear-facing use. However, it’s essential to consider certain factors before making a decision. This review will delve into the key aspects of the Cybex Sirona S, such as its suitability for newborns, its impressive safety features including the load leg and anti-rebound bar, and important considerations like fitting three car seats in a row. We’ll also touch on installation challenges and its suitability for airplane travel.


A convertible car seat that can be used rear-facing and forward-facing


Once the child can sit unassisted


Our recommendation: 6+ months until the seat is outgrown (average 5/6 years old)

What you need to know before you go.

Rear-Facing Seat Stats

  • height limit: 49″
  • weight limit: 50 pounds
  • head height rules: at least 1″ below the top of the headrest

Forward-Facing Seat Stats

  • height limit: 49″
  • weight limit: 65 pounds
  • head height rules: ears must be below the top of the headrest

Other Seat Stats

  • width of seat: 21”
  • weight of seat: 31 pounds
  • crash replacement policy: Replace after any crash.
  • expiration limits: 10 years
  • harness: no rethread
  • lock-off: no
Cybex Sirona S Car Seat Review
car seat Forward-Facing Installation

✅ Seat is good for you if:

✅ You want a swivel seat.
swivel car seat

This seat swivels easily in the rear-facing mode. It is possible to swivel the seat in forward-facing mode, but it’s not as straightforward as it is when rear-facing. If you have the top tether attached, (and we recommend that you do), you will have to loosen it to swivel the seat to the side and then tighten it back when you swivel it back into position. Cybex has said that if you are using the load leg, you can choose to not use the top tether. But without knowing how the seat performs forward-facing with a load leg instead of a top tether, we aren’t sure how that compares as far as crash dynamics.

✅ You have a child who is below the 50th percentile for height.

This seat works best for children who are shorter in stature. The highest harness height is slightly lower than many of the other convertible car seats. It also has a shorter headrest that will be outgrown rear-facing earlier for taller children since this seat does require the child to have at least 1″ of car seat shell above their heads. Below we have a child who is 30 percentile for height and she was able to use this seat until almost 6 rear-facing. But we see many kids outgrow this seat around 2 rear-facing due to the short headrest.

child on car seat

✅ You want a seat with added safety features.

This seat comes with some extras! It is currently the only convertible car seat on the US and Canadian markets that has a load leg. In addition to that, it also has an anti-rebound bar and side impact pods.

🚩 Use Caution If:

🚩 You need to fit 3 people in one row of the vehicle.

With one of the side impact protection pods (LSP) extended, this seat is 21″ wide. It’s not going to fit well in most 3 across configurations. If you did manage to fit it, you definitely would not be able to utilize the swivel function. If you need to fit 3 across, you can find some better options here.

🚩 You have a child that is above the 50th percentile for height.

This seat has a slightly lower harness height than most of the other convertible car seats on the market. In addition, the headrest is on the shorter side, so taller children tend to outgrow this seat rear-facing by the 1″ rule before they get anywhere near the height or weight limit. For these reasons, this seat is best for children who are below the 50th percentile for height.

🚩 You want to use a convertible seat from birth.

We have found that this seat does not fit newborns well as they tend to slump in this seat. The slumping causes the newborns to have a chin to chest position which can cause breathing problems. There are some convertible seats that can fit from birth. You can check out our reviews for Cosco Scenera Next or Clek Foonf. But in the Convertible Buying Kit, we also note which car seats fit newborns well.

🚩 You have a vehicle that doesn’t allow the use of load legs.

There are a handful of vehicles that do not allow load legs to be used. Vans with stow-and-go seating and some trucks with underfloor storage will sometimes forbid the use of load legs. Check your vehicle owner’s manual for more information.

⭐️ Stand Out Features:

⭐ anti-rebound bar

The anti-rebound bar is an added safety feature for rear-facing that can reduce the secondary movement of the car seat, called rebound, during a crash. When a collision occurs, the car seat will move forward, towards the front of the vehicle, and rotate downward. And as we all know from high school physics, every action has an equal and opposite reaction — so after that initial movement, the car seat will rebound, or “bounce back” towards the backrest of the vehicle seat.

The ARB minimizes this bounce-back effect, helping limit the movement of the car seat and your child inside it! ARBs may also limit the side-to-side rotation of the car seat in a side-impact collision. Overall, it’s a great feature on a rear-facing car seat!

⭐ load leg

load leg is a pole that comes down from a car seat and rests on the vehicle’s floor. Load legs reduce crash forces which offer additional protection, especially for your child’s head, neck, and spine. This is currently the only convertible car seat on the US and Canadian markets that has a load leg. You can use it in both the rear and forward-facing positions.

⭐ SensorSafe Chest Clip

This seat comes with the SensorSafe chest clip. This unique chest clip communicates with an app on the caregiver’s phone to provide four types of information: if the child is too hot or too cold; if the child has been buckled in for too long; if the chest clip is unbuckled; or if the child is still buckled in the car after the vehicle has been turned off. These alerts can bring major peace of mind!

Sensorsafe Chest Clip

⚠️ Quirks to be Aware Of:

⚠️ Challenging Installation in Some Vehicles

Despite the tension panel that is supposed to make installation easier, we have found that it’s not always possible to get a tight seat belt installation with this seat and it tends to vary by vehicle. If you are having trouble installing it, you can try a video chat with Cybex before returning it. It is possible to install with the lower anchors instead of the seat belt; but that method has a 30 lbs limit for rear-facing and a 35 lbs limit for forward-facing, so that wouldn’t be a long-lasting option.

Cybex Sirona S Car Seat Review

✈️ Airplane Use

The US version of the Cybex Sirona S is not an FAA-approved car seat. The Canadian version can be used in an aircraft, however, we would not recommend it. It is very heavy and likely too bulky to fit in most airplane seats. Here are some of the seats that we do recommend for airplane travel. For help with all things airplane travel and car seats, check out our Wheels Up Course and private Facebook group.

SITS Bottom Line

The Cybex Sirona S car seat presents a compelling choice for parents and caregivers seeking safety and convenience. Its swivel function, particularly in rear-facing mode, makes it a standout feature for ease of use. However, it’s essential to note that this seat is best suited for children below the 50th percentile for height. The impressive safety features, including the anti-rebound bar and load leg, provide additional peace of mind in the event of a crash.

In summary, the Cybex Sirona S offers innovative safety features and convenience, but it’s essential to consider your specific needs and circumstances when choosing a car seat.

Similar Seats:

  • Cybex Sirona S (Canada)*
  • Cybex Sirona M (US)- Despite the similar name, this is a very different seat. This one does fit newborns well. But it’s quite difficult to install with the seat belt. It does not swivel. It does not have an anti-rebound bar or a load leg.

*A SITS recommended seat. Recommended seats are in our Buying Kits because they have ranked high on our vehicle, child, ease of use, and features scale.

Compare Car Seats

Looking to compare car seats and narrow down the best car seat for your family? The Convertible Car Seat Buying Kit walks you through our 7Cs of car seat selection, then on to an interactive quiz, and finally, a recommended car seat list is generated just for you! If you are overwhelmed and sick of spending hours researching and reading car seat reviews like this one, the Buying Kit will guide you to Safe in the Seat’s recommended car seats for you in under 30 minutes!

Check out this Amazon Live for more convertible seats we recommend and the standout features we love.

car seats on sale
Daily Car Seat Sales

A note about crash-tests

How does the Cybex Sirona S perform in crash tests? 

Well, that’s a great question. We know it passes the strict federally required testing for all car seats sold in the United States. But we don’t know exactly how it performs. That data isn’t released by any official sources in the US — not by car seat manufacturers, government agencies like NHTSA, or anywhere! 

A few third-party websites claim to offer objective crash test data that compares car seats. But we ignore that data at Safe in the Seat for a few reasons. First of all, third-party car seat crash tests don’t actually give us meaningful data! Car seat manufacturers crash-test their products hundreds, even upwards of a thousand times. They crash test the finished product in every single installation configuration using every applicable-sized crash test dummy, not to mention a whole lot of testing at each stage of the development process too. So one or two crash tests completed by another organization just can’t give the same level of information! One or two crash tests aren’t going to represent the overall average performance of any car seat across its lifespan.

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