In California, it's either CHAINS REQUIRED,or no chains required. There is no in-between. The CHP determines when chains become necessary and, after that, all vehicles must put on their chains. On duals, only the outer one is required. No snow tires are acceptable.
Can be very bad when you don't have chains and you are caught in a sudden snow storm. You have to sit there alongside the road until you either purchase some from vendors waiting there just for this situation or wait until the roads are opened up by the CHP. Don't ask me how I know this...