Firstly wanted to say, how sad anything like this is, and how sad it is that you can't turn back time.
This is not aim at any speculation about this particular crash, but it is something that I don't know the answer to, and hoping that someone might know the answer.
Are there regulations in place that define the minium tread on aircraft tyres? I say this, I know how difficult it is to control a car that has very little tread, let alone an aircraft.