http://www.motoringfile.com/2015/01/...ts/#more-38442


I don't have warm and fuzzies over this considering I pick up my son and he rides in a car seat in the back.

 

I hear you. Mine was built in June. I can't imagine what changed between builds in May and June.

 

As per one of the posts at motoringfile:

"Called MINI USA, they're not giving much info but they did indicate the repair would take approximately an hour and is specific to the rear panels in the interior. They would not advise whether/not it was safe to have passengers in the rear seat at this time."

 

I would not get concerned about this. I'll try to explain why.

There is a lot of information about this on the nhtsa website so, seeing as its all in the public domain, I'm going to quote some of it.

First of all see Mini's communications to dealers on this:-

http://www-odi.nhtsa.dot.gov/acms/cs...4V815-6046.pdf


The interesting thing here is that they explicitly state this does NOT apply to the Cooper S. Now this really sparked my interest, especially when you consider what the differences are between the two models and that the bodyshells are essentially the same.

Next, take a look at this document, which is the non-compliance report:-

http://www-odi.nhtsa.dot.gov/acms/cs...4V815-9329.PDF



This refers to side impact test specification FMVSS 214 Section 7.2.6(b) limit of 82G being exceeded by 0.17g.

If you hold out your arm and then let it swing down, your hand is accelerating with 1g. Take 17% of that and that is the acceleration by which this test is failing. Or to put it another way its failing by 0.17/82*100 = 0.2% which in my opinion is well within the margin of error of such a test. However a margin of error is not allowed for in the spec, it either passes or fails, and therefore the car failed the test. In the real word I think this makes practically no difference to how you would fair in a real crash. There are so many other factors that come into play that I really would not worry about it.

The spec for the test can be found here :

http://www.gpo.gov/fdsys/pkg/CFR-200...sec571-214.pdf

Section 7.2.6 defines what this 82g limit refers to - it the lateral lower spine acceleration of a female adult dummy located in the rear seat.

So, I come back to why BMW thinks this does not apply to the Cooper S, the way the test is performed, and the particular test the car failed marginally -all these pieces of information gives us a clue what is going on here. It is not just about the car's structure having the ability to absorb the impact energy. It comes down to simple physics which also partially explains why its so hard for small cars to pass this test - and that is mass! The heavier the car the better it will both absorb the energy and lower the resulting accelerations will be experienced by the occupants. And - the Cooper S is heavier than the Cooper in standard trim - bigger engine - one extra cylinder - bigger wheels, higher equipment etc. The car is so marginal on the limit of the test, this difference appears enough to limit the failure to comply to the standard only to the Cooper.

In fact if you refer back to the chronology, BMW elude to this as they mention variations in equipment levels and vehicle GVWR (gross vehicle weight).

BMW also elude to the fix - they will likely insert some energy absorbing foam behind the interior rear side panels. Such foam is already fitted in the doors and other places.

 

Fantastic explanation.

As an owner of a 2015 F56 Justa, I am not concerned.

However, I do have to wonder what changed in the June timeframe that they stopped there.

Thanks for all the time you spent to make your post.

 

I can think of a few possibilities, but it might just be that over the course of their own testing BMW knew the car was close to the limit and made some minor modifications in production to increase the margin. It could simply be a few extra spot welds, different steel composition/thickness for a few key components or similar. Equipment levels may have changed also as it was getting close to the 2015 changeover, was it not?

 

We're gonna keep you around for a bit cadet ;-) well done.

 

Have a look at the video of the side impact test

http://www.safercar.gov/Vehicle+Shop...vehicleId=8798

A few things are apparent from that if you look closely:-


1) Deformation of the side to the car does not look too bad and there will be minimal, if any intrusion of the cabin area occupied by the rear seat passenger. Lower deformation actually means the car is absorbing less energy and a higher proportion will get used to accelerate the car sideways. So ironically a stiffer structure can be worse for the occupants.

2) The car is literally launched sideways at high speed by the impact. The occupant is literally going to get a fair whack from the interior trim from that.

3) A fair few bits of trim have been removed to help with installing the test instrumentation in the car - making it lighter


It also occurs to me the type of surface on which the vehicle is standing, the size and type of tyre fitted and even the ambient/tyre temperature are going to have a huge effect on the co-efficient of friction between the vehicle and the ground, which will also have a huge effect on the rate with which the vehicle is accelerated sideways - even the number of wheels and for how long that stay in contact with the ground. In the video the surface appears to be concrete which is much slippier than tarmac.

Just goes to show the huge number of variables involved in this and the complexity of the testing. No wonder its not an exact science and mistakes are made.

 

SpaceCadet for President! I guess I'm OK I don't have a back seat lol.

 

Gold star for spacecadet.

 

Nice overview and analysis!

 

I've been a member of this forum for 6 years, and that has to be one of the best, if not the best, post I've seen! You are not an engineer type person, are you :-) Thank you!