Chain control laws might seem straight forward. If there is chain control and you have a two wheel drive car you need chains. But there are a few details that might not seem so apparent. First let me state that this is California chain control laws , which I am covering. Most other states do not have as strict of laws, especially pertaining to passenger vehicles.
Three levels of chain control exist R1,2 and 3.
-R1 states that any vehicles over 6000lbs must have chains on. If you are towing a trailer you must have chains on. If your trailer has brakes you must have chains on the trailer.
-R2-all vehicles except 4 wheel drives need chains. 4wd's need to carry chains (though this is not usually enforced, I have been stopped once and turned around cause I was not carrying chains in an AWD car).
-R3-All Vehicles need chains.
Usually the road is closed before R3 control statuses are reached.
Because of durability, traction and cost, most large commercial trucks run ladder type chains . In fact cables are not allowed on large trucks and trailer. In most cases chains are only required on the outside tire of a dual tire (4) axle, or dually. A common trick used by truckers is to drive the inside tires up on a set of blocks. This puts the outside tire off the ground, making chain installation much easier.
So next time you are driving in the snow and you can not stop, get stuck, or spin out, just know that there are traction aides available.