Cybex Sirona Gi i-Size Review UK.
Premium rotating ERF, tested.

This review is based on seven months of testing in a VW Golf and a Toyota RAV4. We also reference ADAC and Which? safety test data where available. A car seat should always be professionally fitted — free fitting checks are available at many Halfords stores. For broader context see our ERF car seats guide and car seat safety guide.

Full specifications

In-depth review — seven months tested

Installation and ISOFIX

The Sirona Gi installs via ISOFIX connectors and a mandatory support leg — no belt installation option. The ISOFIX click is clear and confirmed by a visual green indicator on both sides. The support leg deploys easily and adjusts to uneven floor surfaces. In both cars we tested (a VW Golf and a Toyota RAV4), installation was stable, took under three minutes once familiar, and required no tools.

The mandatory support leg is a limitation in some vehicles — cars with under-seat storage compartments or flat-folding rear seats may not support the leg safely. Always check the Cybex vehicle compatibility tool before purchasing. This is the most important pre-purchase step for any rotating seat, and is worth doing before committing £500.

The rotation mechanism

Rotation is handled by a lever on the side of the seat that releases the base, allowing the seat to spin 360°. One hand operates it — important because the other is usually occupied holding a child. The mechanism is smooth throughout the full rotation range and locks firmly at every position. After seven months of daily use with no stiffening or degradation in the action, it is clearly well-engineered.

In practical terms, being able to rotate the seat to face the car door, strap the child in, and rotate back to rear-facing takes significantly less physical effort than loading a child rear-facing into a fixed seat — particularly relevant for parents with back pain or limited mobility, and for the later stages when a child weighs 15kg+.

Rear-facing performance

The Sirona Gi accommodates children rear-facing from birth (with the newborn insert) to 105cm — typically 3.5–4 years for most children. The recline range for rear-facing use is generous at 12 positions, which matters for newborns who need a near-flat position and for sleeping toddlers who benefit from a more reclined angle. The headrest adjusts smoothly and the harness height adjusts automatically with the headrest — no re-threading required.

At the upper end of the rear-facing range (85–105cm), children’s legs fold at the knee over the seat shell, which is safe and normal for rear-facing use and causes no discomfort in practice. This is sometimes raised as a concern but is not a safety or comfort issue.

Safety testing results

The Sirona Gi has been tested by ADAC — Germany’s equivalent of Which? and the most rigorous independent car seat testing body in Europe. The seat scores highly across categories. Side-impact performance, which is where i-Size seats must meet stricter requirements than R44, is where the Gi’s engineering is most apparent. The extended side wings and energy-absorbing foam liner in the shell deliver notable protection beyond the i-Size minimum standard.

Which? has also assessed it positively. Neither rating is publicly numeric in the most recent cycles but the qualitative assessments are consistent: this is one of the better-performing rotating ERF seats in current independent testing.

Comfort and child experience

The seat is well-padded — side bolsters support a sleeping child without the head flopping forward, which is one of the most frequent complaints about toddler car seats. The fabric is breathable for a car seat (a low bar, but the Gi passes it better than some competitors). The newborn insert is generously padded and appropriately shaped for very young infants. One small note: the harness buckle is stiffer than average when new and softens with use — it may frustrate some children initially who want to clip it themselves.

The weight and footprint

At 13.5kg the Sirona Gi is heavy — rotating seats with their base mechanism inevitably are. Moving it between cars is a two-hands exercise. If you regularly transfer a seat between vehicles, a lighter fixed seat is more practical. For families with one car who install and leave it, the weight is irrelevant day-to-day.

Category scores

Gi vs Sirona T i-Size — what changed

The Sirona Gi is the current generation, superseding the Sirona T. The headline changes are meaningful rather than cosmetic:

Extended rear-facing range: the Gi is now R129 Phase 1 and Phase 2 certified, meaning it formally covers a wider height range than the Sirona T. In practical terms both rear-face to 105cm, but the regulatory coverage is broader on the Gi.

Improved side-impact protection: the Gi’s shell design has deeper side wings with revised energy-absorbing foam. The improvement is real — the ADAC side-impact scores for the Gi are better than for the Sirona T.

Revised harness routing: the Gi’s harness adjustment is slightly smoother than the T’s, and the headrest-to-harness coupling is more positive in feel. This is a minor refinement rather than a significant change.

Price: the Gi launched at approximately £50 more than the Sirona T at equivalent trim levels. The improvements justify the difference for families buying new. Second-hand Sirona T seats (whose history you can verify) remain a strong option at 50–60% of new Gi pricing.

Who the Sirona Gi is for — and who should look elsewhere

Frequently asked questions