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Why don't child seats in Groups II and III have a harness if this is safer?

¿Por qué las sillas del grupo 2/3 no llevan arnés si es más seguro?


From the time they are born, infants travel in child restraint systems secured by 5-point harnesses until they can move up to seats in Groups II and III. What is the reason for this changeover? Is a harness really safer than a conventional seat belt?

Group I child seats can be used up to a weight of 15-18 kilos. From then on, the child should start using a child restraint system in Group II (15-25 kg) and then Group III (22-36 kg) (check out the different types of seats here). Obviously in these cases we are talking about child restraint systems that have been certified in line with the R44/04 standard, which is guided by weight, while the R-129 standard refers to height (don't forget that the child's seat should be changed whenever he or she exceeds the maximum weight established by the manufacturer or when their head goes higher than the top of the CRS).
Child seats in Group O+ and Group I generally secure the child with a -point harness while seats in Groups II and III use the vehicle's seat belt. As a general rule, from the time the child reaches around 15 kilos they are secured in a different way. 

The truth is that the most efficient systems are those with the five-point harness. Indeed, this is the system chosen for competition vehicles. The reason is that they restrain the body much more in every direction in the event of a collision: they prevent the body from moving upwards and sideways, and in the case of children they stop them sliding downwards. In fact, they prevent the well-known submarining effect and distribute the load of the impact between the shoulders, hips and pelvis. Consequently they are particularly efficient in preventing abdominal injuries.

On the other hand, the 3-point belt is also a safe option but to a lesser extent than the 5-point one. So why don't the other child seats have this type of harness? The explanation lies in the fact that as the child weighs more, the harness needs to expend a greater effort in restraining them and hence the seatback supporting the child needs to be more resistant.
It is considered that from the time a child reaches a weight of 15 kg, it's body is strong enough to withstand the force of a seat belt. However, given that seat belts in cars today are designed for adults, smaller children need assistance for them to fit correctly: child seats in Groups II and III. In contrast, the harness of child seats in Group I is no longer present even though this is the best option.
This does not mean that securing a child in a child seat with the vehicle's seat belt is unsafe. The best option is always for the child to be seated in a child restraint system suitable for their height and weight. While it is a good idea to delay the move to a Group II seat as long as possible (provided that the child does not exceed the maximum weight and height established by the manufacturer), it is also dangerous to put a child in a seat that is not the most appropriate one and is too small, as they would not be properly protected in the event of an impact.
If you put a child in a child seat that is too big, for example in a Group II seat before they have reached 15 kg, you will find that the child's body is not ready to withstand the force exerted on it by a seat belt in the event of an accident. Furthermore, the child would not be secured adequately as due to the child's height the belt would almost certainly not be positioned correctly and may even cause injuries. Apart from this, you should also bear in mind the increased safety that a harness offers. The same situation applies in the opposite direction, i.e. if the child weighs more than 18 kg and is still traveling in a Group I seat. In this case, the harness would not be strong enough to support the child's weight.


In this respect, you should bear in mind that for both harnesses and seat belts to be completely secure they must be properly buckled. Remember that a tight harness is a safe harness. Here you will find some tips on buckling a harness correctly.
With regard to the seat belt, the seat must be installed and the child secured according to the manufacturer's instructions. Follow these instructions to position the seat belt properly in the case of Group 2 and 3 child seats. Remember that you need to pass the seat belt across the points or guides shown by the manufacturer (they are usually highlighted in color) and ensure that the seat belt is properly affixed. The upper strap should not lie too close to the neck and the lower strap should rest over the pelvic bones, not the stomach. This helps to avoid potential injuries, especially abdominal ones.
At all times you should avoid strapping in the child when they have a coat on as this would give a false sense of security.


Given the importance of the harness and the need to offer the greatest possible safety, we have been talking recently about the Secureguard, a fourth anchoring point.
Some child restraint systems in Groups 2 and 3 offer a harness that goes between the legs and serves as a fourth anchoring point for the seat belt. It prevents the abdominal section from moving out of place on the journey, keeping it secured in the right position. It helps to reduce the force exerted on the abdomen in the event of a collision.
As with five-point harnesses, this central piece eliminates the submarining effect and avoids the belt slipping up over the belly, keeping it in the lower abdomen area.

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