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.
In America they say you can twist the buckle stalk up to 3 times to avoid buckle crunch, what is your opinion on this?
Hi ERF Mama, it is not recommended in the UK to twist the buckle stalk to prevent buckle crunch. Any twists in the seat belt, including buckle stalk can cause the restraint to not work correctly. Twisting the buckle stalk can also cause instability in the fitting.
Brilliant post, unfortunately I have seen this all too often, there seems to be a view that as long as the belt goes over and clicks in it doesn't matter about anything else, I wonder if many new parents are even aware of the risk of this?
Hi Thomas, glad you liked the post! Unfortunately lots of parents are not aware of the danger, it is only with posts like this and parents who are aware spreading the word that we can help people spot when their child's car seat may not be safe – so be sure to share with your friends
I have been told that buckle crunch is not an issue for group 2-3 seats. Is this right? Our new car has unusually long 'female' sides to the seat belts so will always touch the frame of the seat. Both Halfords and Mothercare say it is not an issue but surely the risk that the buckle will spring open in an impact us still there? Don't know how to get them shortened and can't ask the manufacturer as it's a 20 year old Japanese import. Hope you can help.
You have received correct information, if the buckle touches a high back booster it is fine, as the booster is a belt positioning device that just needs to lift the child up, it is not held tightly back with the seat belt.
Any other questions don't hesitate to ask
I have a Nissan Almera tino with long belt buckle webbing causing buckle crunch, I need a seat for a newborn, we have tried the britax first class but there's only one rearward facing seat belt route therefore we cannot eliminate buckle crunch with that seat until it's forward facing. We've tried pretty much every possible seat in Halfords and Mothercare. Do you have any advice other than getting a new car? Many thanks (7 months pregnant, baby arriving 13th October and currently no car seat!!)
Brilliant article and I bet 90% of people don't know about this. I went to buy a rearward facing group 1 yesterday and the staff at Mothercare who were brilliant couldn't fit it because of buckle crunch. They pointed out my 1 year old is in a seat base that has buckle crunch. I have fitted his maxi cosi cabriofix with just the belt now but it doesn't feel very secure without the base. I am really worried I won't be able to get any group 1 to fit my 07 fiesta. Ford say they can't help and have never heard of it. Any ideas?
As you are specifically looking for rear facing group 1 car seats we would recommend that you contact a local independent nursery retailer who stocks extended rear facing seats, as they tend to have more choice than major retailers. Also, it may be possible for you to have ISOfix retrospectively fitted in your Fiesta by a Ford dealership – this would then eliminate the need to use the seat belt and will remove the worry of buckle crunch.
It’s great to hear about the fab service you received from Mothercare!
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