When child seats are fitted with the adult seat belt, it must be the webbing of the seat belt holding the seat in place, not the seat belt buckle. If any part of the plastic seat belt buckle casing is on or over the plastic frame of the seat, it is an unsafe fit, which is called buckle crunch.
Buckle crunch typically happens in vehicle's that have the female buckle on a long stalk, causing it to protrude out of the vehicle seat.
However, buckle crunch can happen on buckles with a shorter stalk, if the wrong car seat is used.
Buckle crunch is dangerous, because the plastic casing of the seat belt buckle is bent on or over the plastic of the child seat. This puts pressure on the casing, and in a collision, the casing could shatter - causing the car seat to not be safely restrained.
The seat on the left is the Maxi Cosi Tobi, which is a forward facing group 1 seat that often avoids buckle crunch. The seat on the right is the Axkid Minikid, which is a rear facing group 1,2 car seat that also often avoids buckle crunch.
If your vehicle has ISOFIX, it is useful to use it, as this removes the need for the adult seat belt. It is important to visit a retailer to buy an ISOFIX seat, as not all ISOFIX seats fit all cars. ISOFIX child restraints are normally classed as 'Semi Universal', and have a vehicle compatibility list.
If you have checked your child’s car seat and found it has buckle crunch (example above), try fitting it in a different seating position in the car. Occasionally the seat belt buckle length differs, and moving the seat to a different position solves the problem.
You can also check your model of child seat, on some seats there may be several ways to secure it, with one of those methods avoiding buckle crunch.
As an example, the Britax First Class has an alternative buckle routing:
No, only seats which use harness to restrain the child, and occasionally an impact shield, can have buckle crunch. It is dangerous because the seat belt is holding the child seat in place, and the child seat is restraining the child with a harness. In a collision, this puts a lot of pressure and force on the child seat, seat belt and buckle.
High back boosters and booster cushions do not get buckle crunch, because the booster is simply a 'belt positioning' device, which lifts the child up so the adult belt can fit them safely.
It is not dangerous for the buckle to sit over the frame of a high back booster - although you do need to make sure the buckle doesn't sit under and behind the frame of the seat, as this gives an unnatural belt route.
Hi I have a maxi cosi axiss car seat for my two year old that can only be installed using the seat belt it fitted great in my Renault megane but I have recently changed my car to a bmw 320 and now there is really bad buckle crunch.my car seat was very expensive and I don't really want to replace it any suggestions??
Thanks for getting in touch,
We have not normally experienced buckle crunch in a BMW, would you be able to take a photo of the problem side of the seat belt fitment to allow us to see if we can make any suggestions? If your child seat has buckle crunched, unfortunately there is not much that can be done, other than fitting the seat on the other side of the car – occasionally buckle length can differ from side to side of the vehicle.
Hi, I was told this was an issue with my son's car seat when on a plane. Does anyone know of a car seat that is compatible with the lap belts on airplanes? He is two years old and about 14kg.
Hi Melissa, Seats that would be suitable for use on the plane would be the Britax Prince, the Britax Eclipse and the Kiddy series – these seats are all suitable for your child’s weight and are allowed to be used with a lap belt. You may need to contact the manufacturer for the TUV/FAA sticker to show the seat is approved, and always check with the airline before taking your seat and get confirmation that you are allowed to use it on the plane.
Hello, we went to Mothercare today to look at stage 0-1+ car seats, as our original car seat for our son seems a little on the small side for him now! There was a mothercare car seat that was fine in the rear facing position but not in the forward facing when we would need to turn it round, apparently there was buckle crunch, but we'd never heard of it before. Tried others in my 2000 Vauxhall Astra and seems to be a problem across most if not all car seats! What am I supposed to do?! Adding isofix points and putting an isofix car seat is probably worth month than my car itself!!
Any advice appreciated.
Thank you for your comment!
Some vehicles can be particularly tricky to fit seats into, particularly if you have an issue with buckle crunch. What does your son weigh? We may able to recommend some seats for you to take a look at that will fit your car, avoiding the buckle crunch issue. Also, will the seat be fitted into any other cars?
We have a 2002 Astra which has long seat belt stalks. Mothercare recommended the Britax First Class, which has an alternative routing for long stalks. We've been using it for the last two years without any problems.
We have a 2010 Qashqai, and are having problems getting a next stage carseat for my almost three year old.
He weighs just over 15 kilos and is getting too big for his current seat (MaxiCosi Priori) – his head is already over the top of the back of the seat and he’s quite long too. Anyway, I am keen to get a group 2/3 carseat as it would suit us and other children, rather than a group 3 seat, but I’m having huge problems.
There seems to be a common problem with this year and model of car that the seat belt stalks are very long and causing potential buckle crunch with every seat we are trying in mothercare. They said there has to be at least 1cm between the buckle and the base of the car seat – a bit different to the photos you have here as the problem in our car seems borderline but they are still not happy to sell us a seat.
I’ve been on the phone to Nissan for weeks now trying to find out if we can have the seat belt stalks lowered or replaced with those from the newer Qashqai models, which are shorter, but to no avail – they just keep saying they can’t recommend a car seat but recommend isofix.
My problem is that you also need to use the seatbelt with an isofix carseat – once he gets to 20 kilos he will no longer use a 5-point harness and will rely on the seatbelt, so surely there are buckle crunch issues with an isofix seat too? Ie that in a collision, the buckle could crunch against the seat and snap off, releasing my son?
Please could you let me know any advice on this as it’s driving me insane – we’ve tried so many seats and it’s getting quite frustrating.
Thanks a lot in advance.
Thanks for getting in contact
The Nissan Qashqai does suffer from buckle crunch on some models, and the seat belt buckle must be clear of the frame of the child car seat. In group 1 mode (harness seats) this is a concern as the seat belt is holding both seat and child in place and restraining both – there is a huge amount of pressure on the buckle which can cause it to fail. Buckle crunch doesn’t occur in group 2,3 mode (high back booster) as the seat belt is only restraining the child, and the booster is just positioning the child to correctly fit within the seat belt – there is very little pressure applied to the buckle.
Your son does sound like he’s very nearly out of his Maxi Cosi car seat – this is at 18kg, or when his eyes are level with the top of the car seat. A high back booster may be used from 15kg so long as the child fits within the seat and seat belt correctly, we would not recommend this for a 3 year old however. Children are safer remaining in a harnessed car seat, which is why group 123 is such a good option for lots of parents.
There is an ISOfix group 123 car seat soon to be released, it is from Britax and is called the Advansafix. It allows the harness to be used to 25kg and it also converts to a high back booster. This car seat fits with ISOfix and top tether – so you would need a top tether point in your car, it does also require the seat belt to be used in conjunction with the ISOfix attachment, so it will be important to try this seat in your car before you buy.
If you have any other questions don't hesitate to ask
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