180 to 190 rear tire

[colirv]

I very much doubt they would look any further than tread depth, unless of course you go way over or under size (something obvious).

In most instances I'm sure you're right. However, although the chances may be very small, you might end up crippling a child. If an insurance company is faced with paying a multi-million pound/dollar award they will find any excuse not to pay. Sure, you should be able to argue that the size of the tyre did not contribute to the accident, if indeed it didn't, but why take even the slightest risk of crippling debt for the rest of your life in order to save an entry on your insurance form and perhaps peanuts in extra premium?