[spenner]

There is slightly more to this than what has been mentioned above, what was also explained at the drivers briefing was the following:
Firstly there is no rule, as this has never been required. There is however a rule in the ifmar rule book.
So what was mentioned is that due to one manufacturer the dimensions that ifmar run to will be added to the brca off road. All manufacturers are aware of the dimensions, which is why they make wheels and tyres which all fit on each other's cars/wheels etc.

I know that people have been waiting for the outcome before deciding on what future wheels/tyres they do.