system.

So, they'll measure the tread thickness and tell you if they think the difference might cause damage.

Some states have laws about cracked windshields, others don't. With states that do the only time a person will be warned or receive a ticket for it is if they get stopped for something else and then the cop notices the crack. Normally, that would just be a warning. If a crack is more than 15" or so long, I'd have it replaced.