Illegal here, made a few years ago. It usually takes a fatality for them to make a rule change like that...but I've never heard or seen anyone use a car tyre on a motorcycle here. It would also come under a modification rule...non standard tyre type. Not much boring straight roads here, NZ riding is all about the corners, so no need for a tyre not based on handling. Personally I don't have a problem with people using a car tyre on a bike, apart from price, I don't see a reason to do it.