what is the benefit of isofix in a group 2/3 seat?

[squealingpiglets]

I understand the benefit of isofix in a group 0 or 1 seat where the child is in a 5 point harness as the isofix ensures the car seat is correctly fitted & will restrain the seat in an accident, thus it is safer than non isofix.

However, in a group 2/3 seat where it is the adult seatbelt that will restrain the child and seat in an accident, what extra benefits does isofix bring over a seat without it? These seats dont need to be fitted in the same way as the group 0/1 so the safety risk of incorrect fitting is already eliminated.

ps I realise it stops the seat moving around when the child's not in it. But are there any other safety benefits? thanks

Biggest thing is when it is unoccupied, it's quite a big projectile and would be a lot heavier than it's actual weight in even a low speed bump.
It is a PITA to remember to secure the seat when unoccupied, so Isofix does help in that respect.

sorry x posted. No other benefits that I can think of sorry!

Purely the irritation factor of having to sort seat when not in use by child- so not an issue if you only drive with child in that car and put seat in every time.

Don't underestimate what a pita it is to strap the seat in every time it's not in use.
Isofix will stop it sliding around and stop it tipping as they get in and out.

They feel more stable. My DC have isofix seats but sometimes use them in family members' cars that don't have isofix. They feel really wobbly, i.e if DC leans over (to poke DSibling ), the whole seat tips over. This doesn't happen when the isofix is used.

I don't think I did ever strap the seat in when it wasnt in use...oops! Don't need them now thankfully

It doesn't make the seat safer in use. Just as other posters have mentioned, it's a right pain in the area to remind the children to plug the seatbelts back in every time they leave the car because they always forget.

The projectile thing is huge imo.

Isofix states that it's only suitable for child plus seat < 33kg - but when the child is in the seat, they'll be using the car's seatbelt by the time they're in a group 2/3, so it's not relevant.

As PP have mentioned, isofix in a HBB is just to stop the seat being a projectile in a crash when there's no child in it. When there's a child in it, the child and the seat holding the child's weight are restrained by the adult seat belt.

Just to clarify for anybody else reading, group 0 and 1 isofix car seats are not safer than belt fitted car seats if both are installed correctly. They are equally safe. However, isofix reduces the likelihood of human error when installing the seat so isofix seats are less likely to be installed incorrectly. Doesn't mean they can't be installed incorrectly!

Another point, just because your car has isofix doesn't mean that all isofix seats will fit in it. Belt fitted car seats can often get a much better fit in a car, particularly those with sloped seats.

Sorry for the derail OP! I just think it's important this information gets to as many people as often as possible.

no probs tea thanks for clarifying re risks of incorrect installation, you explained it much better than me!

and thanks to everyone who replied, we already have isofix HBB, so good to know it was the better choice - I couldn't be doing with the faff of belting in a seat each time its not in use!

IME there is a slight fitting benefit too, in that it keeps the seat in the right place in the car. When you have a loose HBB especially if you're cramming lots of passengers into a small car, or have the child getting themself in you can end up with the seat in the wrong place which might cause the seatbelt to fit awkwardly. (Mainly it's annoying as the 5yo whines that they can't get the seatbelt in properly because they've pushed the seat over the buckle but won't accept help )

I believe it is technically called iso fit.

Plugging in empty car seats is only for people who aim for perfection though isn't it? I have never heard of anyone doing that. Ours are caught by the seat belt feeder at the shoulder and won't go further than the back of the seat in front.

I once saw a jeep that was in a minor accident- it looked like it had mounted the curb in the middle of a roundabout swerving to avoid another car- the booster seat from the back was rammed up around the front seat. I was so surprised at how much it had moved on what looked like a minor enough accident.

I think you're right eggs in that not many people actually do it. You should though, and having the seatbelt hooked into the top isn't really enough because that little clip isn't designed to secure the weight of the entire seat (plus even if it did hold it, it would still swing forwards at the bottom).

If I'm right - and I might be wrong, GCSE physics was a long time ago... the formula for working out the mass of an object moving at speed is to multiply half the weight (in kilos) by the speed (in metres/second, squared).

So average booster seat = 4.5kg, 30mph = 13.4m/s - squared = about 180

2.25 x 180 = 405

That's 405 kg of mass slamming into the back of your front passenger/driver.

I know what you mean though. I know DH never fixes DS's booster seat in when he's in the car alone.

It's not just boosters anyway it's any loose object in the car.

Dogs, apparently, are particularly a problem for becoming projectiles. I did a thing about it at work a few years ago. If you don't have your dog behind a grate in the boot you should have them in an approved car harness (the latter possibly being the safer solution for the dog...)

@itsboiledeggsagain. In January I flipped my car in the ice and ended up in a ditch upside down. Ds1 was in his seat in the back but ds2's hbb was empty and tethered only by the seatbelt guide at the top. The seat was flung up against Ds1 when we overturned and only the very large side impact protection of his own seat stopped it from pinning him and crushing his chest. He was stuck and unable to get his own seatbelt off until a policeman climbed in through the boot and moved the seat out by force. Luckily we had no injuries but if we were going faster or another car was involved it could have been very different.

I will never again leave an unoccupied seat unsecured in the car.

Pascha I get what you are saying and that is food for thought as sometimes ds1 is in without his older siblings. I also enjoyed the physics too - thanks!

I have had a nasty accident with 2 smalls in and was very glad they were erf.

Sorry pascha I should have said I hope you are all OK now.

Thanks @itsboiledeggsagain. I know I was incredibly complacent before. No-one ever thinks it will happen to them and it did. Both of our hbbs are isofix now.